**1. Introduction**

The demand of green chemistry for applying in the pharmaceutical and the other chemical industries is increasingly vital due to the fact that our world faces the environmental challenges of the twenty-first century. US Environmental Protection Agency (EPA) has suggested green chemistry for innovative technologies that reduce toxic, undesired waste, and environmental impact. Green chemistry is thus getting grew as an open light to afford a huge scientific area. After EPA, 12 principles of green chemistry have been gotten more attention and these principles have been considered more seriously by pharmaceutical companies since 1998. Pharmaceutical companies declared that they should improve the environmental performance by utilizing green chemistry. Not only pharmaceutical companies but also the other chemical industries started to take a step for green chemistry due to its advantages such as decreasing of waste and cost. It is assumed that green chemistry can save the industry an

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

estimated USD 65.5 billion by 2020 [1] primarily by reducing manufacturing costs. If the processes can be implemented right, green chemistry can afford to reduce waste product and decrease the resources consumption. Green chemistry is needed for minimizing of some social risks and safety issues, as well.

that this planet needs a balance of nature. Every attempt to heart this balance will come across more serious effects. That is why we need greener strategies and greener thinking. In this chapter, we have discussed the importance of solvents and catalysts for synthetic strategy at pharmaceutical chemistry. The progress and advantages about green solvents and bio- and organic-catalysts will be included in detail and we hope that whole of this knowledge will be

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In every product development processes and different industrial applications, solvents are needed in huge amounts resulting in abundant amounts of waste. Innovative technologies and different synthetic strategies have discussed solventless methods which are not accepted for all areas of research due to some market concerns. After the solventless ideas, chemists and medicinal scientists have searched out for solvents which suit green chemistry. According to Fischer, green solvent expresses the target to minimize the environmental impact coming from the consuming of solvents in chemical production [9]. Some strategies have emerged for solvents which can be mentioned as green. These are substitution of hazardous solvents resulting in more eco-friendly, biodegradable, and/or minimizing of ozone depletion potential, use of biosolvents (oleochemicals), and substitution of organic solvents which are super-

In the literature, many examples of green solvents can be seen for forming natural products, medicines, and important intermediate products which can be used for further synthesis.

Vegetable oils are oleochemicals which are extracted from many plants' seeds. They are renewable resources and have triglyceride structure in which three hydroxyl groups of glycerol are substituted with different fatty acids that make them liquids or solid products [11]. Vegetable oils are important food ingredient. Unfortunately, they have not considered as a green solvent so far except for a reaction which was published by us [12]. Vegetable oils have been utilized for biopolymers and might be evaluated by scientists who are looking for a new

We have described the acylation and cyclization reaction that has been run in vegetable oil, especially corn oil. Utilization and advantages of vegetable oils have been discussed and yields, reaction times, and sustainability of vegetable oils have been compared both with each other and with toxic solvent, xylene. This reaction is the first example of vegetable oils and this idea should be concerned by more synthetic strategies due to the cost and efficacy of

A mixture of dibenzoylmethane (**1**), oxalyl chloride (**2**), and phenol (**3**) was heated in corn oil

of compound **1** was acylated very easily.

a hand for both medicinal scientists and pharmaceutical industries.

**2. Synthetic strategies with green solvents**

critical fluids and ionic liquids [10].

**2.1. Vegetable oils as a green solvent**

source of green solvent.

vegetable oils (**Scheme 1**) [12].

at 120°C for 15 min. Authors have explained that CH2

In the past decade, some of the large pharmaceutical companies around the world have focused on using green chemistry processes for drug discovery, development, and manufacturing. These firms include Amgen, the Merck Group, Abbott, Eli Lily, Johnson & Johnson, and Roche [2]. Green chemistry has started to point three lines such as cost, mankind, and our planet. American Chemical Society's Green Chemistry Institute's Pharmaceutical Roundtable was therefore launched and, since 2008, many drug companies have become the members that aim to foster the development of more efficient, less polluting processes. Fortunately, green chemistry celebrates 25 years of progress on 2016 [3].

It can not be denied that people need medicines to cure their diseases some of which are very unpleasant. For that reason, pharmaceutical industry has struggled to have modern synthetic strategies for known and unknown therapeutic reagents. On the other hand, although many successful methodologies were achieved, the toxic properties of many reagents and solvents were not known and the issues of waste minimization and sustainability of solvents and/or unreacted reagents were largely unheard. Chemists and medicinal scientists can reduce the risk to human health and the environment by following all the valuable principles of green chemistry. The most simple and direct way to apply green chemistry in pharmaceuticals is to utilize eco-friendly, nonhazardous, reproducible, and efficient solvents and catalysts in the synthesis of drug molecules, and in researches involving synthetic chemistry.

It has become clear that the chemical and related industries such as pharmaceutical companies are faced with environmental problems. There are a lots of synthetic methodologies and they have generated abundant amounts of waste and chemical industries want to minimize or eliminate this waste. Sheldon has discussed that in the pharmaceutical industries, there is an urgency for consideration of the waste product as a number of by-products produced per kg of product (designated E factor) is about 25 [4]. Innovative strategies on chemistry are the core of the pharmaceutical business. The main point is gathering technology and chemistry to improve lives of patients and minimize environmental impact.

Solvents and stoichiometric reagents are the most important parameters to be considered for greener strategies and these parameters are under investigation in detail by many pharmaceutical companies such as Sanofi-Aventis [5, 6] and GlaxoSmithKline [7]. These companies have suggested that conventional solvents such as halogenated, petroleum-based should be converted into greener solvents such as glycerol, ethyl lactate [8], and water [9]. A catalyst is an another crucial parameter which reduce the amount of inorganic salts and/or reagents. Green alternative for consuming of stoichiometric salts and reagents is to use a catalyst and this issue has been considered by pharmaceutical companies. However, demanding of the least expensive reagents has limited the applying of catalysts to be used widely.

Future perspective of green chemistry will be extended more seriously in many research areas. Product and environment should be considered together and it should be remembered that this planet needs a balance of nature. Every attempt to heart this balance will come across more serious effects. That is why we need greener strategies and greener thinking. In this chapter, we have discussed the importance of solvents and catalysts for synthetic strategy at pharmaceutical chemistry. The progress and advantages about green solvents and bio- and organic-catalysts will be included in detail and we hope that whole of this knowledge will be a hand for both medicinal scientists and pharmaceutical industries.

### **2. Synthetic strategies with green solvents**

estimated USD 65.5 billion by 2020 [1] primarily by reducing manufacturing costs. If the processes can be implemented right, green chemistry can afford to reduce waste product and decrease the resources consumption. Green chemistry is needed for minimizing of some social

In the past decade, some of the large pharmaceutical companies around the world have focused on using green chemistry processes for drug discovery, development, and manufacturing. These firms include Amgen, the Merck Group, Abbott, Eli Lily, Johnson & Johnson, and Roche [2]. Green chemistry has started to point three lines such as cost, mankind, and our planet. American Chemical Society's Green Chemistry Institute's Pharmaceutical Roundtable was therefore launched and, since 2008, many drug companies have become the members that aim to foster the development of more efficient, less polluting processes. Fortunately,

It can not be denied that people need medicines to cure their diseases some of which are very unpleasant. For that reason, pharmaceutical industry has struggled to have modern synthetic strategies for known and unknown therapeutic reagents. On the other hand, although many successful methodologies were achieved, the toxic properties of many reagents and solvents were not known and the issues of waste minimization and sustainability of solvents and/or unreacted reagents were largely unheard. Chemists and medicinal scientists can reduce the risk to human health and the environment by following all the valuable principles of green chemistry. The most simple and direct way to apply green chemistry in pharmaceuticals is to utilize eco-friendly, nonhazardous, reproducible, and efficient solvents and catalysts in the

It has become clear that the chemical and related industries such as pharmaceutical companies are faced with environmental problems. There are a lots of synthetic methodologies and they have generated abundant amounts of waste and chemical industries want to minimize or eliminate this waste. Sheldon has discussed that in the pharmaceutical industries, there is an urgency for consideration of the waste product as a number of by-products produced per kg of product (designated E factor) is about 25 [4]. Innovative strategies on chemistry are the core of the pharmaceutical business. The main point is gathering technology and chemistry to

Solvents and stoichiometric reagents are the most important parameters to be considered for greener strategies and these parameters are under investigation in detail by many pharmaceutical companies such as Sanofi-Aventis [5, 6] and GlaxoSmithKline [7]. These companies have suggested that conventional solvents such as halogenated, petroleum-based should be converted into greener solvents such as glycerol, ethyl lactate [8], and water [9]. A catalyst is an another crucial parameter which reduce the amount of inorganic salts and/or reagents. Green alternative for consuming of stoichiometric salts and reagents is to use a catalyst and this issue has been considered by pharmaceutical companies. However, demanding of the

Future perspective of green chemistry will be extended more seriously in many research areas. Product and environment should be considered together and it should be remembered

least expensive reagents has limited the applying of catalysts to be used widely.

synthesis of drug molecules, and in researches involving synthetic chemistry.

improve lives of patients and minimize environmental impact.

risks and safety issues, as well.

74 Green Chemistry

green chemistry celebrates 25 years of progress on 2016 [3].

In every product development processes and different industrial applications, solvents are needed in huge amounts resulting in abundant amounts of waste. Innovative technologies and different synthetic strategies have discussed solventless methods which are not accepted for all areas of research due to some market concerns. After the solventless ideas, chemists and medicinal scientists have searched out for solvents which suit green chemistry. According to Fischer, green solvent expresses the target to minimize the environmental impact coming from the consuming of solvents in chemical production [9]. Some strategies have emerged for solvents which can be mentioned as green. These are substitution of hazardous solvents resulting in more eco-friendly, biodegradable, and/or minimizing of ozone depletion potential, use of biosolvents (oleochemicals), and substitution of organic solvents which are supercritical fluids and ionic liquids [10].

In the literature, many examples of green solvents can be seen for forming natural products, medicines, and important intermediate products which can be used for further synthesis.

#### **2.1. Vegetable oils as a green solvent**

Vegetable oils are oleochemicals which are extracted from many plants' seeds. They are renewable resources and have triglyceride structure in which three hydroxyl groups of glycerol are substituted with different fatty acids that make them liquids or solid products [11]. Vegetable oils are important food ingredient. Unfortunately, they have not considered as a green solvent so far except for a reaction which was published by us [12]. Vegetable oils have been utilized for biopolymers and might be evaluated by scientists who are looking for a new source of green solvent.

We have described the acylation and cyclization reaction that has been run in vegetable oil, especially corn oil. Utilization and advantages of vegetable oils have been discussed and yields, reaction times, and sustainability of vegetable oils have been compared both with each other and with toxic solvent, xylene. This reaction is the first example of vegetable oils and this idea should be concerned by more synthetic strategies due to the cost and efficacy of vegetable oils (**Scheme 1**) [12].

A mixture of dibenzoylmethane (**1**), oxalyl chloride (**2**), and phenol (**3**) was heated in corn oil at 120°C for 15 min. Authors have explained that CH2 of compound **1** was acylated very easily.

Jerome et al. have reported some common synthetic reactions on glycerol and they have discussed yield, reaction time, and sustainability of glycerol. One of the reactions that researchers have carried out was a nucleophilic attack on the β position of α,β-unsaturated carbonyl molecule. This type of reaction can be seen in many organic reactions and derivatization of lead compounds in pharmaceutical industries. The reaction showed that crude glycerol gave yield of the reaction up to 81% and reuse of glycerol as third time for same reactions did give

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Selectivity and green perspective of the reaction were evaluated by researchers. It is obvious that the reaction aforementioned was progressed in high yield on glycerol and the other organic solvents such as toluene, DMF, and DMSO did not produce any amount of

Glycerol is used for different reactions and demands on different application fields can be surpassed with modification of glycerol with simple thinking. This modification was done by Garcia et al. [16]. Garcia and his group have synthesized some alkylated derivatives of glycerol to be used as a solvent and evaluated their physical and chemical properties for further

Organochalcogens are under investigation because of the importance of organochalcogen which includes one of an atom of Group 16 in the periodic table which are O, S, Se, and Te. Ebselen and its analogs are important molecules which show significant beneficial effects in primate model of neurodegenerative diseases (**Figure 1**) [17–19]. Organoselenium compound **12** is currently in clinical trials for cardiovascular indications [17]. The importance of these molecules has opened an area for the furnishing of

With this respect, Leonardo et al. have described a green protocol without base and metal in

glycerol for obtaining of organoselenium derivatives (**Scheme 4**) [19].

**Scheme 3.** Nucleophilic attack to the α,β-unsaturated carbonyl group in glycerol [15].

the yield of the product perfectly (**Scheme 3**) [15].

expected product.

applications.

these types of molecules.

**Scheme 1.** Acylation reaction in corn oil [12].

#### **2.2. Glycerol as a green solvent**

Glycerol (also named as glycerin) is a polyalcohol and second part of oleochemicals which are derived from natural oils. Glycerol has been utilized in many different fields such as pharmaceutical and food industry, tobacco, and cellulose films [13]. Sustainability and low-cost of glycerol make it a good green solvent. With this respect, pharmaceutical companies and chemists have gotten more attention for glycerol as alternative to other organic solvents which are hazardous, volatile compounds, toxic, and harmful. Despite the fact that glycerol is a solvent and selected for many reactions, there are some obstacles which chemists and medical scientists have to overcome: (i) due to the viscosity of glycerol, it should be fluidified with a co-solvent. On the other hand, glycerol is much less viscous up to 60°C and reactions can be proceeded at temperatures higher than 60°C; (ii) glycerol might join the reaction as a reagent, as it has three OH groups which can be mentioned as acidic sites; (iii) glycerol has an enough length and donor atom in which it can obtain complexes with metal catalysts resulting in unwanted side products and/or unreactivity of catalysis. It can be said that there are two sides of glycerol and those can be mentioned for every solvents and reagents which are used in research areas. However, in here, we want to display advantages of glycerol in synthetic strategies.

Safaei et al. synthesized *4H*-pyrans with catalyst-free, one-pot and three-component strategy using glycerol as green solvent (**Scheme 2**) [14]. Yield of reactions are high up to 93% and reactions gave many different types of pyran derivatives. Furthermore, authors have tested the reaction in water and they have seen that yield of the reactions was decreased down to 70%.

Cyclization reaction under atom economic and green solvent procedure is so important and this kind of reactions has prompted medicine scientists to reorganize the strategy for drug design.

**Scheme 2.** One-pot and three-component strategy in glycerol [14].

Jerome et al. have reported some common synthetic reactions on glycerol and they have discussed yield, reaction time, and sustainability of glycerol. One of the reactions that researchers have carried out was a nucleophilic attack on the β position of α,β-unsaturated carbonyl molecule. This type of reaction can be seen in many organic reactions and derivatization of lead compounds in pharmaceutical industries. The reaction showed that crude glycerol gave yield of the reaction up to 81% and reuse of glycerol as third time for same reactions did give the yield of the product perfectly (**Scheme 3**) [15].

Selectivity and green perspective of the reaction were evaluated by researchers. It is obvious that the reaction aforementioned was progressed in high yield on glycerol and the other organic solvents such as toluene, DMF, and DMSO did not produce any amount of expected product.

**2.2. Glycerol as a green solvent**

76 Green Chemistry

**Scheme 1.** Acylation reaction in corn oil [12].

Glycerol (also named as glycerin) is a polyalcohol and second part of oleochemicals which are derived from natural oils. Glycerol has been utilized in many different fields such as pharmaceutical and food industry, tobacco, and cellulose films [13]. Sustainability and low-cost of glycerol make it a good green solvent. With this respect, pharmaceutical companies and chemists have gotten more attention for glycerol as alternative to other organic solvents which are hazardous, volatile compounds, toxic, and harmful. Despite the fact that glycerol is a solvent and selected for many reactions, there are some obstacles which chemists and medical scientists have to overcome: (i) due to the viscosity of glycerol, it should be fluidified with a co-solvent. On the other hand, glycerol is much less viscous up to 60°C and reactions can be proceeded at temperatures higher than 60°C; (ii) glycerol might join the reaction as a reagent, as it has three OH groups which can be mentioned as acidic sites; (iii) glycerol has an enough length and donor atom in which it can obtain complexes with metal catalysts resulting in unwanted side products and/or unreactivity of catalysis. It can be said that there are two sides of glycerol and those can be mentioned for every solvents and reagents which are used in research areas. However, in

Safaei et al. synthesized *4H*-pyrans with catalyst-free, one-pot and three-component strategy using glycerol as green solvent (**Scheme 2**) [14]. Yield of reactions are high up to 93% and reactions gave many different types of pyran derivatives. Furthermore, authors have tested the reaction in water and they have seen that yield of the reactions was decreased down to 70%. Cyclization reaction under atom economic and green solvent procedure is so important and this kind of reactions has prompted medicine scientists to reorganize the strategy for drug design.

here, we want to display advantages of glycerol in synthetic strategies.

**Scheme 2.** One-pot and three-component strategy in glycerol [14].

Glycerol is used for different reactions and demands on different application fields can be surpassed with modification of glycerol with simple thinking. This modification was done by Garcia et al. [16]. Garcia and his group have synthesized some alkylated derivatives of glycerol to be used as a solvent and evaluated their physical and chemical properties for further applications.

Organochalcogens are under investigation because of the importance of organochalcogen which includes one of an atom of Group 16 in the periodic table which are O, S, Se, and Te. Ebselen and its analogs are important molecules which show significant beneficial effects in primate model of neurodegenerative diseases (**Figure 1**) [17–19]. Organoselenium compound **12** is currently in clinical trials for cardiovascular indications [17]. The importance of these molecules has opened an area for the furnishing of these types of molecules.

With this respect, Leonardo et al. have described a green protocol without base and metal in glycerol for obtaining of organoselenium derivatives (**Scheme 4**) [19].

**Scheme 3.** Nucleophilic attack to the α,β-unsaturated carbonyl group in glycerol [15].

Wolfson et al. have reported the compatibility of glycerol in some named reactions such as nucleophilic substitution, reduction, catalytic reduction, Heck reaction, Asymmetric hydrogenation, and transesterification [21]. They have concluded that glycerol was successfully employed as versatile and alternative green solvent in a variety of organic reactions and synthetic methodologies. In addition, they have said that high products conversions and selec-

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Functional group protection is still crucial in all fields of industries. Carbonyl protection can be progressed with a reaction between a molecule having a carbonyl group and 1,2- or 1,3-dithiole. Perin et al. have successfully applied a green protocol for protection of carbonyl group. Researchers have done the protection of ketones in glycerol (**Scheme 6**) [22]. Protection of carbonyl group of cyclohexanone (**19**) with 1,2-dithiole (**20**) was achieved in glycerol with

More recently, Gu et al. have described a cyclization reaction in glycerol in which a threecomponent strategy was utilized for pyran derivative **25** (**Scheme 7**) to occur [23]. Reactions were run with styrene (**22**), dimedone (**23**), and *p*-formaldehyde (**24**). The yield of the product was based on selected solvent and the most suitable solvent was selected as glycerol in which yield was seen as 68%. The other solvents showed less yield than glycerol. Furthermore, sustainability of glycerol was also tested and after three runs, yield was recorded to be found as 65%. An intermediate product of the reaction between dimedone and p-formaldehyde is formed and this intermediate product forms the pyrane ring by cyclizing with the styrene.

To furnish pyrazolo-pyrane derivative **30**, Lu and his group have designed a reaction in which pyrazolone **28**, styrene analog **29**, and *p*-formaldehyde **24** were reacted in glycerol (**Scheme 8**) [24]. Reaction was progressed at 110°C and yield of the reaction was calculated as 78%. Same reaction in solvent-free and ionic liquids gave no product and was 48%, respectively. Pyrazolone derivative **28** was taken place by the reaction between phenyl hydrazine (**26**) and ethyl acetoacetate (**27**) through well-known condensation. Pyrazolone was not isolated and trapped with

Glycerol and its etheric derivatives have been utilized both as a solvent and as a reagent for industrial processes and mg-scale synthetic reactions [25]. Unfortunately, glycerol is not still stood on the top of the industry due to some disadvantages such as viscosity, reactivity, and capability of being a ligand for metals. We hope that chemists and medical scientists will find

tivities were achieved [21].

good yield, 85% [22].

styrene analog **29** [24].

**Scheme 6.** Protection of carbonyl group with 1,2-dithiole in glycerol [22].

**Figure 1.** Two examples of organochalcogens.

**Scheme 4.** Synthesis of organoselenium derivative in glycerol [19].

N,N-dimethylaniline (**13**) and haloselenium compound **14** was reacted in glycerol under an inert atmosphere to give organochalcogen molecule **15**. Waste product was HCl and yield of the reaction was excellent, 99%. Furthermore, the energy needed for running of the reaction was minimum, which was room temperature.

When scientists dig an unknown knowledge which has already existed, they have come across unexpected results. One of these situations was reported by Wolfson et al. One of the most important reactions is obviously hydrogenation of organic compounds in which catalysts and molecular hydrogen have been used. Wolfson et al. have achieved hydrogenation of benzaldehyde in glycerol which was used both solvent and hydrogen donor reagent using ruthenium catalyst (**Scheme 5**) [20].

This reaction represents a green protocol as glycerol has been used as both solvent and reagent resulting in atom economic strategy. It was seen that while glycerol oxidized to 1,3-dihydroxy-acetone (**18**), the reaction gave benzyl alcohol (**17**), one of the most important starting materials for organic reactions.

**Scheme 5.** Hydrogenation of benzaldehyde with catalyst and glycerol [20].

Wolfson et al. have reported the compatibility of glycerol in some named reactions such as nucleophilic substitution, reduction, catalytic reduction, Heck reaction, Asymmetric hydrogenation, and transesterification [21]. They have concluded that glycerol was successfully employed as versatile and alternative green solvent in a variety of organic reactions and synthetic methodologies. In addition, they have said that high products conversions and selectivities were achieved [21].

Functional group protection is still crucial in all fields of industries. Carbonyl protection can be progressed with a reaction between a molecule having a carbonyl group and 1,2- or 1,3-dithiole. Perin et al. have successfully applied a green protocol for protection of carbonyl group. Researchers have done the protection of ketones in glycerol (**Scheme 6**) [22]. Protection of carbonyl group of cyclohexanone (**19**) with 1,2-dithiole (**20**) was achieved in glycerol with good yield, 85% [22].

More recently, Gu et al. have described a cyclization reaction in glycerol in which a threecomponent strategy was utilized for pyran derivative **25** (**Scheme 7**) to occur [23]. Reactions were run with styrene (**22**), dimedone (**23**), and *p*-formaldehyde (**24**). The yield of the product was based on selected solvent and the most suitable solvent was selected as glycerol in which yield was seen as 68%. The other solvents showed less yield than glycerol. Furthermore, sustainability of glycerol was also tested and after three runs, yield was recorded to be found as 65%. An intermediate product of the reaction between dimedone and p-formaldehyde is formed and this intermediate product forms the pyrane ring by cyclizing with the styrene.

To furnish pyrazolo-pyrane derivative **30**, Lu and his group have designed a reaction in which pyrazolone **28**, styrene analog **29**, and *p*-formaldehyde **24** were reacted in glycerol (**Scheme 8**) [24]. Reaction was progressed at 110°C and yield of the reaction was calculated as 78%. Same reaction in solvent-free and ionic liquids gave no product and was 48%, respectively. Pyrazolone derivative **28** was taken place by the reaction between phenyl hydrazine (**26**) and ethyl acetoacetate (**27**) through well-known condensation. Pyrazolone was not isolated and trapped with styrene analog **29** [24].

Glycerol and its etheric derivatives have been utilized both as a solvent and as a reagent for industrial processes and mg-scale synthetic reactions [25]. Unfortunately, glycerol is not still stood on the top of the industry due to some disadvantages such as viscosity, reactivity, and capability of being a ligand for metals. We hope that chemists and medical scientists will find

**Scheme 6.** Protection of carbonyl group with 1,2-dithiole in glycerol [22].

**Scheme 5.** Hydrogenation of benzaldehyde with catalyst and glycerol [20].

was minimum, which was room temperature.

**Scheme 4.** Synthesis of organoselenium derivative in glycerol [19].

ruthenium catalyst (**Scheme 5**) [20].

**Figure 1.** Two examples of organochalcogens.

78 Green Chemistry

materials for organic reactions.

N,N-dimethylaniline (**13**) and haloselenium compound **14** was reacted in glycerol under an inert atmosphere to give organochalcogen molecule **15**. Waste product was HCl and yield of the reaction was excellent, 99%. Furthermore, the energy needed for running of the reaction

When scientists dig an unknown knowledge which has already existed, they have come across unexpected results. One of these situations was reported by Wolfson et al. One of the most important reactions is obviously hydrogenation of organic compounds in which catalysts and molecular hydrogen have been used. Wolfson et al. have achieved hydrogenation of benzaldehyde in glycerol which was used both solvent and hydrogen donor reagent using

This reaction represents a green protocol as glycerol has been used as both solvent and reagent resulting in atom economic strategy. It was seen that while glycerol oxidized to 1,3-dihydroxy-acetone (**18**), the reaction gave benzyl alcohol (**17**), one of the most important starting

**2.3. Water as a green solvent**

reactions were described as being on-water [26].

in water at 25°C (**Scheme 9**) [27].

Synthesis of isocoumarin in H2

**Scheme 9.** Wittig reaction in water [27].

rin with yield of 85% (**Scheme 11**) [29].

scaled [28].

Water possesses many unique physical and chemical properties such as extensive hydrogen bonding, high heat capacity, large dielectric constant, and a large temperature window. Water as a solvent has therefore many advantages over conventional organic solvents. Furthermore, water can be selected as a green solvent due to cost, readily available, nontoxic, nonpolluting, and nonflammable. In fact, people do not call water as a chemical. In spite of many important advantages of water, it is still not commonly utilized as a sole solvent for synthetic strategies in research lab and industry as most of the organic compounds are not soluble in water. Nature selects water for its biological reactions and since a century, scientists have tried to mimic the synthetic reactions in water as occurred in nature. Scientists have been away from water for a long time because of an old doctrine in which old chemists say that the insoluble reagents do not yield any product. However, Sharpless has altered this old idea with a new thinking that reactions can be progressed "on" or "in" water means that solubility is not important for reactions [26]. Sharpless has described the reactions such as cycloaddition, Diels-Alder, nucleophilic opening of epoxide and Claisen rearrangement in which as the reactants were not soluble in water, the

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Basic reactions of organic chemistry are utilized in pharmaceutical chemistry to obtain medicines. One of these reactions is Wittig reaction. Wittig reaction is so important and it gives a new C–C bond. Morsch et al. have therefore reported a green protocol for Wittig reaction, run

Pyrrole is one of the most critical starting materials for drug design and its reactions are also so important. For a green strategy, Sobral reported a reaction that pyrrole (**34**) and diethyl ketone (**35**) were reacted in water to get 2,2′-dipyrromethane (**36**) (**Scheme 10**) [28]. Sobral has reported that yield of the reaction was 80% and the reaction was progressed as gram-

tion of salicylic acid (**37**) and alkyne **38** in the presence of ruthenium catalyst gave isocouma-

Pizzo and coworkers described the reaction of aza compound **40** and vinyl ether **41** resulting in pyridazine derivatives as a sole product with 92% for **42** and 6% for **43** and pyrrole derivative

O was reported by Xu et al. They have discussed that the reac-

**Scheme 7.** Three-component strategy in glycerol in order to get pyrene derivative **25** [23].

**Scheme 8.** Synthesis of pyrazolo-pyrane in glycerol [24].

a way for greener alternative. Academicians have an important role in the ability for industry to implement green chemistry while industry can utilize the findings which are reactions, materials, and conditions with industrial relevance, to introduce more sustainable alternatives with lower risk and greener protocols for scale-up productivity.

#### **2.3. Water as a green solvent**

Water possesses many unique physical and chemical properties such as extensive hydrogen bonding, high heat capacity, large dielectric constant, and a large temperature window. Water as a solvent has therefore many advantages over conventional organic solvents. Furthermore, water can be selected as a green solvent due to cost, readily available, nontoxic, nonpolluting, and nonflammable. In fact, people do not call water as a chemical. In spite of many important advantages of water, it is still not commonly utilized as a sole solvent for synthetic strategies in research lab and industry as most of the organic compounds are not soluble in water. Nature selects water for its biological reactions and since a century, scientists have tried to mimic the synthetic reactions in water as occurred in nature. Scientists have been away from water for a long time because of an old doctrine in which old chemists say that the insoluble reagents do not yield any product. However, Sharpless has altered this old idea with a new thinking that reactions can be progressed "on" or "in" water means that solubility is not important for reactions [26]. Sharpless has described the reactions such as cycloaddition, Diels-Alder, nucleophilic opening of epoxide and Claisen rearrangement in which as the reactants were not soluble in water, the reactions were described as being on-water [26].

Basic reactions of organic chemistry are utilized in pharmaceutical chemistry to obtain medicines. One of these reactions is Wittig reaction. Wittig reaction is so important and it gives a new C–C bond. Morsch et al. have therefore reported a green protocol for Wittig reaction, run in water at 25°C (**Scheme 9**) [27].

Pyrrole is one of the most critical starting materials for drug design and its reactions are also so important. For a green strategy, Sobral reported a reaction that pyrrole (**34**) and diethyl ketone (**35**) were reacted in water to get 2,2′-dipyrromethane (**36**) (**Scheme 10**) [28]. Sobral has reported that yield of the reaction was 80% and the reaction was progressed as gramscaled [28].

Synthesis of isocoumarin in H2 O was reported by Xu et al. They have discussed that the reaction of salicylic acid (**37**) and alkyne **38** in the presence of ruthenium catalyst gave isocoumarin with yield of 85% (**Scheme 11**) [29].

Pizzo and coworkers described the reaction of aza compound **40** and vinyl ether **41** resulting in pyridazine derivatives as a sole product with 92% for **42** and 6% for **43** and pyrrole derivative

**Scheme 9.** Wittig reaction in water [27].

a way for greener alternative. Academicians have an important role in the ability for industry to implement green chemistry while industry can utilize the findings which are reactions, materials, and conditions with industrial relevance, to introduce more sustainable alternatives

**25**

**Scheme 7.** Three-component strategy in glycerol in order to get pyrene derivative **25** [23].

80 Green Chemistry

with lower risk and greener protocols for scale-up productivity.

**Scheme 8.** Synthesis of pyrazolo-pyrane in glycerol [24].

**Scheme 10.** Dipyrromethane synthesis in water [28].

Yields of the reactions were varied between 74 and 95% [32]. They have synthesized spiroketal enol derivative **50** with the same strategy using furane ring, as well. Reactions were run in

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83

Lactam is an important ring as it is a part of antibiotic medicines such Cefaclor. With this respect, Pirrung and Sarma have reported the reaction in which acetoacetic acid (**51**), amine **53**, and izonitrile **52** were reacted in water (**Scheme 15**). The reaction was completed in 2 hours with yield of 93%. Authors have described that DCM gave the same result with less yield, 45% [33]. This reaction is a crucial example since it gives lactam in a water medium. Generally

Besides lactam, a lactone is also so crucial ring which scientists want to synthesize. Lactone is presented in many natural and synthetic products which are used as a remedy for diseases. Fujimoto and coworkers studied the cyclization of allyl-iodoacetate using triethylborane in water (**Scheme 16**). Authors claimed that reaction progressed through radical and this is not a recently encountered result [34]. Compatibility of water was tested against some solvents. DMSO, DMF, MeCN, methanol, and benzene gave the cyclic product less than the reaction

which is a valuable synthetic building block, present in many bioactive molecules [36].

The reaction was experimented in both water and 1,4-dioxane, and yield of the reaction in water was 96% while the reaction in 1,4-dioxane was 5%. This derivatization was progressed through radical reaction and as said before, the radical reaction in water really challenges and

of isatin was converted into oxime group (**Scheme 17**)

water with the addition of a small amount of hexafluoro-2-propanol (**Scheme 14**).

speaking, lactam ring is susceptible for ring opening toward nucleophile.

in water.

Wei and co-workers [35] reported that CH2

**Scheme 14.** Synthesize of chromene derivative in water [32].

**Scheme 13.** On water reaction of benzothiazole [31].

thanks to scientists, these hard reactions have been achieved.

**Scheme 11.** Synthesis of isocoumarin in water [29].

**44** as a by-product with 2%. Authors reported that the reaction proceeded under heterogeneous medium because of poor solubility of aza compound **40** and vinyl ether **41** as called on-water reaction (**Scheme 12**) [30].

Synthesis of benzothiazole ring **47** was published by Patel and co-workers on water [31]. The reaction was started with iodo-benzo-isothiocyanate (**44**) and morpholine (**45**) to get thiourea derivative **46** which was not isolated. Thiourea derivative was cyclized with CuO-nanocatalyst using K2 CO<sup>3</sup> on water with yield of 92% (**Scheme 13**). They have also reported some points which were stereoselectivity, reusable catalyst, and no chromatographic purification because of high yields. They have also screened the effects of different solvents such as dioxane, DMF, and toluene which gave yields of 63, 70, and 55%, respectively [31].

Qu and his group studied the chromene derivative **49** in water. The reaction was named as highly green due to the fact that toxic solvent, catalyst, additive, and base were not used.

**Scheme 12.** Diels-Alder reaction of aza compound and vinyl ether "on-water" [30].

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**Scheme 13.** On water reaction of benzothiazole [31].

Yields of the reactions were varied between 74 and 95% [32]. They have synthesized spiroketal enol derivative **50** with the same strategy using furane ring, as well. Reactions were run in water with the addition of a small amount of hexafluoro-2-propanol (**Scheme 14**).

Lactam is an important ring as it is a part of antibiotic medicines such Cefaclor. With this respect, Pirrung and Sarma have reported the reaction in which acetoacetic acid (**51**), amine **53**, and izonitrile **52** were reacted in water (**Scheme 15**). The reaction was completed in 2 hours with yield of 93%. Authors have described that DCM gave the same result with less yield, 45% [33]. This reaction is a crucial example since it gives lactam in a water medium. Generally speaking, lactam ring is susceptible for ring opening toward nucleophile.

Besides lactam, a lactone is also so crucial ring which scientists want to synthesize. Lactone is presented in many natural and synthetic products which are used as a remedy for diseases. Fujimoto and coworkers studied the cyclization of allyl-iodoacetate using triethylborane in water (**Scheme 16**). Authors claimed that reaction progressed through radical and this is not a recently encountered result [34]. Compatibility of water was tested against some solvents. DMSO, DMF, MeCN, methanol, and benzene gave the cyclic product less than the reaction in water.

Wei and co-workers [35] reported that CH2 of isatin was converted into oxime group (**Scheme 17**) which is a valuable synthetic building block, present in many bioactive molecules [36].

The reaction was experimented in both water and 1,4-dioxane, and yield of the reaction in water was 96% while the reaction in 1,4-dioxane was 5%. This derivatization was progressed through radical reaction and as said before, the radical reaction in water really challenges and thanks to scientists, these hard reactions have been achieved.

**Scheme 14.** Synthesize of chromene derivative in water [32].

**Scheme 12.** Diels-Alder reaction of aza compound and vinyl ether "on-water" [30].

and toluene which gave yields of 63, 70, and 55%, respectively [31].

reaction (**Scheme 12**) [30].

**Scheme 10.** Dipyrromethane synthesis in water [28].

**Scheme 11.** Synthesis of isocoumarin in water [29].

CO<sup>3</sup>

using K2

82 Green Chemistry

**44** as a by-product with 2%. Authors reported that the reaction proceeded under heterogeneous medium because of poor solubility of aza compound **40** and vinyl ether **41** as called on-water

Synthesis of benzothiazole ring **47** was published by Patel and co-workers on water [31]. The reaction was started with iodo-benzo-isothiocyanate (**44**) and morpholine (**45**) to get thiourea derivative **46** which was not isolated. Thiourea derivative was cyclized with CuO-nanocatalyst

which were stereoselectivity, reusable catalyst, and no chromatographic purification because of high yields. They have also screened the effects of different solvents such as dioxane, DMF,

Qu and his group studied the chromene derivative **49** in water. The reaction was named as highly green due to the fact that toxic solvent, catalyst, additive, and base were not used.

on water with yield of 92% (**Scheme 13**). They have also reported some points

reaction is one of the promising reactions those run in water. The reaction's yield was calcu-

The Role of Green Solvents and Catalysts at the Future of Drug Design and of Synthesis

Mishra and Verma have introduced a reaction for example of tetracyclic ring. Benzofuran derivative **63** and ortho-phenylendiamine (**64**) were reacted in water to get tetracyclic molecule with 88%. Solvent was tested for yield of the reaction and they have recorded that most of the proper solvents were water and the others were resulted in decreasing of the product

unsatisfactory. They have optimized the reaction and explained that there was no need for

It is obvious that we can not mention all literature about green solvents, but we have desired to focus the most important literature. Exceptions for vegetable oil, glycerol and water have been considered more in detail in which we have given some important synthetic strategies. In next sub-section, we will share some examples of the other solvents which are pointed as

Ionic liquids are organic salts which are liquid at ambient temperatures. They are nonvolatile, nonflammable, thermally and chemically stable which make them as a better alternative for green chemistry than conventional organic solvents. Due to their high polarity, it can be used in many chemical and biochemical reactions. Besides special properties, they show less solubility in water and are generally immiscible with many organic solvents such hexane(s). They are much more viscous than other organic solvents which might be due to more hydrogen bonds and Van der Waals interactions. The most important feature of ionic liquids is that they can be tuned by changing cation, anion, and alkyl part, in which it is possible to obtain many manipulated green

On the other hand, to tune the physical properties of ionic liquids, they have combined with hydrogen donor reagents such as glycerol (**68**), oxalic acid (**69**), and urea (**67**). This green alternative emerged because of the volatility of organic solvents. Ionic liquids are called deep eutectic solvents (DES) when composed by a quaternary ammonium salt and a hydrogen bond donor (**Figure 3**) [40]. There are some common combinations for DES which can be seen

More recently, ethyl lactate **70** (**Figure 4**) was introduced as a potential green solvent to extract

organic solvents [39]. Some common cation and anion parts are presented in **Figure 2**.

in **Figure 2**. They have been composed by different amounts of each part.

some natural ingredients from vegetable by Gan and co-workers [8].

**Scheme 18.** Synthesis of indole ring [37].

and result of catalyzed reaction was

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85

lated as 92% and derivatization of indole was also studied (**Scheme 18**) [37].

down to 45%. Reaction was also studied using AgNO<sup>3</sup>

catalyst, additive, and toxic solvent (**Scheme 19**) [38].

green solvents such as ionic liquids, ethyl lactate, and so on.

**2.4. The other solvents as mentioned in green chemistry**

**Scheme 15.** Synthesis of lactam ring in water [33].

**Scheme 16.** Yielding of lactone derivative [34].

**Scheme 17.** Conversion of isatin into oxime-isatin **59** [35].

Chen et al. have synthesized C-2 substituted indole derivatives **62** through a reaction in which aniline derivative **60** and organoboron salt **61** were used in water. For the acidity of the medium, tosyl acid was utilized and palladium acetate was consumed as a catalyst. This reaction is one of the promising reactions those run in water. The reaction's yield was calculated as 92% and derivatization of indole was also studied (**Scheme 18**) [37].

Mishra and Verma have introduced a reaction for example of tetracyclic ring. Benzofuran derivative **63** and ortho-phenylendiamine (**64**) were reacted in water to get tetracyclic molecule with 88%. Solvent was tested for yield of the reaction and they have recorded that most of the proper solvents were water and the others were resulted in decreasing of the product down to 45%. Reaction was also studied using AgNO<sup>3</sup> and result of catalyzed reaction was unsatisfactory. They have optimized the reaction and explained that there was no need for catalyst, additive, and toxic solvent (**Scheme 19**) [38].

It is obvious that we can not mention all literature about green solvents, but we have desired to focus the most important literature. Exceptions for vegetable oil, glycerol and water have been considered more in detail in which we have given some important synthetic strategies. In next sub-section, we will share some examples of the other solvents which are pointed as green solvents such as ionic liquids, ethyl lactate, and so on.

#### **2.4. The other solvents as mentioned in green chemistry**

Ionic liquids are organic salts which are liquid at ambient temperatures. They are nonvolatile, nonflammable, thermally and chemically stable which make them as a better alternative for green chemistry than conventional organic solvents. Due to their high polarity, it can be used in many chemical and biochemical reactions. Besides special properties, they show less solubility in water and are generally immiscible with many organic solvents such hexane(s). They are much more viscous than other organic solvents which might be due to more hydrogen bonds and Van der Waals interactions. The most important feature of ionic liquids is that they can be tuned by changing cation, anion, and alkyl part, in which it is possible to obtain many manipulated green organic solvents [39]. Some common cation and anion parts are presented in **Figure 2**.

On the other hand, to tune the physical properties of ionic liquids, they have combined with hydrogen donor reagents such as glycerol (**68**), oxalic acid (**69**), and urea (**67**). This green alternative emerged because of the volatility of organic solvents. Ionic liquids are called deep eutectic solvents (DES) when composed by a quaternary ammonium salt and a hydrogen bond donor (**Figure 3**) [40]. There are some common combinations for DES which can be seen in **Figure 2**. They have been composed by different amounts of each part.

More recently, ethyl lactate **70** (**Figure 4**) was introduced as a potential green solvent to extract some natural ingredients from vegetable by Gan and co-workers [8].

**Scheme 18.** Synthesis of indole ring [37].

**Scheme 16.** Yielding of lactone derivative [34].

**Scheme 15.** Synthesis of lactam ring in water [33].

84 Green Chemistry

**Scheme 17.** Conversion of isatin into oxime-isatin **59** [35].

Chen et al. have synthesized C-2 substituted indole derivatives **62** through a reaction in which aniline derivative **60** and organoboron salt **61** were used in water. For the acidity of the medium, tosyl acid was utilized and palladium acetate was consumed as a catalyst. This

**Scheme 19.** Synthesis of tetracyclic molecule **65** in water [38].

They have studied ethyl lactate for green extraction and they have reported that understanding of its extraction capability and applicability should be improved. This solvent was experimented for plant extraction and might be tested in chemistry and pharmaceutical

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Catalyst is one of the rules of green chemistry and it should be considered by chemists and medical scientists [41]. There are two types of catalysts: heterogeneous and homogeneous. Homogeneous catalysts are more effective to obtain expected products than heterogeneous catalysts. However, isolation and reusable of homogeneous catalysts are the more problematic disadvantages when used for fine chemicals production in the chemical and pharmaceutical industry because of metal contamination of products. Less effective but more attractive heterogeneous catalysts are more favorable due to some of their advantages which are reusable and easier isolation from the medium. Besides heterogeneous catalyst, as a semi-heterogeneous catalyst, nanocatalysts have taken more attention as they have large surface-volume ratio resulting in more interactions between the surface of catalyst and reactant. However, there is still a contamination of catalyst even if it is filtered using specific filtration methods. More recently, thanks to magnetism, magnetic nanocatalysts have been obtained and extracted from medium with external magnetic field [42–46]. They have given more promising solution for chemical industries and it seems to be good candidates for active pharmaceu-

Sharma et al. introduced a cyclization reaction using nanocatalyst [48]. They have obtained oxazole derivatives **73** with the reaction between benzyl amine (**71**) and methyl acetoacetate (**72**). Nanomagnetic catalyst was characterized by SEM, XRD, and FESEM. They have discussed that the yield of oxazole derivative decreased down to 5% absence of the nanocatalyst. Under reaction condition with nanocatalyst, conversion of the reaction was recorded as 100%

One-step synthesis of xanthones was achieved by Gerbino and coworkers in which copperbased magnetically recoverable nanocatalyst was utilized [49]. Salicylaldehyde and phenol derivatives were reacted in toluene under ligand-free condition (**Scheme 21**). Reusable copper

applications.

**3. Synthetic strategies with catalysts**

**3.1. Nanocatalysts as a green solution**

**Figure 4.** The structure of ethyl lactate.

tical ingredient (API) industry [42, 47].

which means that waste product is not produced (**Scheme 20**).

**Figure 2.** Cations and anions for ionic liquids.

**Figure 3.** Some of the deep eutectic solvents.

**Figure 4.** The structure of ethyl lactate.

They have studied ethyl lactate for green extraction and they have reported that understanding of its extraction capability and applicability should be improved. This solvent was experimented for plant extraction and might be tested in chemistry and pharmaceutical applications.

### **3. Synthetic strategies with catalysts**

#### **3.1. Nanocatalysts as a green solution**

**Figure 2.** Cations and anions for ionic liquids.

**Scheme 19.** Synthesis of tetracyclic molecule **65** in water [38].

86 Green Chemistry

**Figure 3.** Some of the deep eutectic solvents.

Catalyst is one of the rules of green chemistry and it should be considered by chemists and medical scientists [41]. There are two types of catalysts: heterogeneous and homogeneous. Homogeneous catalysts are more effective to obtain expected products than heterogeneous catalysts. However, isolation and reusable of homogeneous catalysts are the more problematic disadvantages when used for fine chemicals production in the chemical and pharmaceutical industry because of metal contamination of products. Less effective but more attractive heterogeneous catalysts are more favorable due to some of their advantages which are reusable and easier isolation from the medium. Besides heterogeneous catalyst, as a semi-heterogeneous catalyst, nanocatalysts have taken more attention as they have large surface-volume ratio resulting in more interactions between the surface of catalyst and reactant. However, there is still a contamination of catalyst even if it is filtered using specific filtration methods. More recently, thanks to magnetism, magnetic nanocatalysts have been obtained and extracted from medium with external magnetic field [42–46]. They have given more promising solution for chemical industries and it seems to be good candidates for active pharmaceutical ingredient (API) industry [42, 47].

Sharma et al. introduced a cyclization reaction using nanocatalyst [48]. They have obtained oxazole derivatives **73** with the reaction between benzyl amine (**71**) and methyl acetoacetate (**72**). Nanomagnetic catalyst was characterized by SEM, XRD, and FESEM. They have discussed that the yield of oxazole derivative decreased down to 5% absence of the nanocatalyst. Under reaction condition with nanocatalyst, conversion of the reaction was recorded as 100% which means that waste product is not produced (**Scheme 20**).

One-step synthesis of xanthones was achieved by Gerbino and coworkers in which copperbased magnetically recoverable nanocatalyst was utilized [49]. Salicylaldehyde and phenol derivatives were reacted in toluene under ligand-free condition (**Scheme 21**). Reusable copper

Some of the most important synthetic strategies are named Suzuki, Heck, and Sonogashira reactions. These strategies give countless methods to chemists and medical scientists for further reactions in which fine chemicals and medicines can be obtained easily and in greener ways. More recently, these reactions have been progressed with magnetic nanocatalyst which

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A green alternative for hydrogenation of π bonds and the nitro group was reported by Baig and Varma [57]. They have experimented lots of double and triple bonds, and nitro groups for reduction to obtain saturated alkyl unit and amine functional groups (**Scheme 23**). For fine chemicals, reduction is a critical reaction and thanks to this reaction, reduction can be done by a nanocatalyst which is magnetically active and can be removed easily with an external

N-aryl oxazolidine-2-ones framework **82** is an important ring which is a part of some clinically used medicines such as linezolid and Rivaroxaban which are sold as antibiotic and anticoagulant, respectively. In this spirit, forming of these rings with green chemistry would be very useful. Sharma's group has therefore studied on that strategy to obtain N-aryl-oxazolidine-2-ones using magnetic nanocatalyst (**Scheme 24**) [58]. They have tested nanocatalyst for reusability and seen that after eight runs, the yield of the product was recorded as 80–85% which was close to the first run, 95% [58]. Anilin (**80**) and ethylene carbonate (**81**) were reacted by means of nanocatalyst and the reaction gave almost quantitative yield. Removing of the nanocatalyst is so easy due to its magnetic feature. The nanocatalyst was made with iron (III) and iron (II) salts and the nano-iron oxide was reacted with silicone derivatives to obtain a silicon-coated nano-iron oxide. After then, imidazole-terminated silicon derivative was bonded to nano-iron oxide. Authors have assumed that nanocatalyst bonds to the oxygen atom of the carbonyl group of carbonate and makes therefore easy

Benzodiazepine substructure is presented in some vital medicines such as diazepam, alprazolam, lorazepam, oxazepam, temazepam, and clonazepam. This structure can be obtained by many different methods [59, 60]. Beside presented methods, green chemistry is in progress to give diazepine derivatives. Lutfullah et al. have published an article in which they have displayed a green reaction using nanocatalyst to obtain tricyclic benzodiazepine derivatives

**85** in good yields (**Scheme 25**). Nanocatalyst is silicon-coated nickel-oxide [61].

are mentioned green strategies [51–56].

magnetic field from reaction medium [57].

attack of aniline to a carbon atom of carbonate.

**Scheme 23.** Reduction reactions with magnetic nanocatalyst [57].

**Scheme 20.** Synthesize of oxazole derivatives on nanomagnetic catalyst [48].

**Scheme 21.** Furnishing of xanthone derivative **76** with copper-based nanocatalyst [49].

nanocatalyst was tested and was found to be 89% effective when used in fourth cycle. Altering of copper nanocatalyst with a conventional catalyst, CuCl or CuO, decreased the yield of the product down to 65 and 62%, respectively.

Quinazolinones **79** were formed with halo benzamide **77** and benzylamine using copper nanocatalyst (CuONPs) by Patel et al. (**Scheme 22**) [50]. Researchers showed that conventional copper catalysts such as CuBr, CuCl, and CuI have a less catalytic effect than copper nanocatalysts. Furthermore, without a catalyst, there is no cyclic product.

**Scheme 22.** Synthesis of quinazolinone ring [50].

Some of the most important synthetic strategies are named Suzuki, Heck, and Sonogashira reactions. These strategies give countless methods to chemists and medical scientists for further reactions in which fine chemicals and medicines can be obtained easily and in greener ways. More recently, these reactions have been progressed with magnetic nanocatalyst which are mentioned green strategies [51–56].

A green alternative for hydrogenation of π bonds and the nitro group was reported by Baig and Varma [57]. They have experimented lots of double and triple bonds, and nitro groups for reduction to obtain saturated alkyl unit and amine functional groups (**Scheme 23**). For fine chemicals, reduction is a critical reaction and thanks to this reaction, reduction can be done by a nanocatalyst which is magnetically active and can be removed easily with an external magnetic field from reaction medium [57].

N-aryl oxazolidine-2-ones framework **82** is an important ring which is a part of some clinically used medicines such as linezolid and Rivaroxaban which are sold as antibiotic and anticoagulant, respectively. In this spirit, forming of these rings with green chemistry would be very useful. Sharma's group has therefore studied on that strategy to obtain N-aryl-oxazolidine-2-ones using magnetic nanocatalyst (**Scheme 24**) [58]. They have tested nanocatalyst for reusability and seen that after eight runs, the yield of the product was recorded as 80–85% which was close to the first run, 95% [58]. Anilin (**80**) and ethylene carbonate (**81**) were reacted by means of nanocatalyst and the reaction gave almost quantitative yield. Removing of the nanocatalyst is so easy due to its magnetic feature. The nanocatalyst was made with iron (III) and iron (II) salts and the nano-iron oxide was reacted with silicone derivatives to obtain a silicon-coated nano-iron oxide. After then, imidazole-terminated silicon derivative was bonded to nano-iron oxide. Authors have assumed that nanocatalyst bonds to the oxygen atom of the carbonyl group of carbonate and makes therefore easy attack of aniline to a carbon atom of carbonate.

Benzodiazepine substructure is presented in some vital medicines such as diazepam, alprazolam, lorazepam, oxazepam, temazepam, and clonazepam. This structure can be obtained by many different methods [59, 60]. Beside presented methods, green chemistry is in progress to give diazepine derivatives. Lutfullah et al. have published an article in which they have displayed a green reaction using nanocatalyst to obtain tricyclic benzodiazepine derivatives **85** in good yields (**Scheme 25**). Nanocatalyst is silicon-coated nickel-oxide [61].

**Scheme 23.** Reduction reactions with magnetic nanocatalyst [57].

**Scheme 21.** Furnishing of xanthone derivative **76** with copper-based nanocatalyst [49].

**Scheme 20.** Synthesize of oxazole derivatives on nanomagnetic catalyst [48].

88 Green Chemistry

lysts. Furthermore, without a catalyst, there is no cyclic product.

nanocatalyst was tested and was found to be 89% effective when used in fourth cycle. Altering of copper nanocatalyst with a conventional catalyst, CuCl or CuO, decreased the yield of the

Quinazolinones **79** were formed with halo benzamide **77** and benzylamine using copper nanocatalyst (CuONPs) by Patel et al. (**Scheme 22**) [50]. Researchers showed that conventional copper catalysts such as CuBr, CuCl, and CuI have a less catalytic effect than copper nanocata-

**Scheme 22.** Synthesis of quinazolinone ring [50].

product down to 65 and 62%, respectively.

Biocatalysts are biodegradable, sustainable, reusable, more efficient, and more stereoselective which means more atom economic than conventional methods. With this respect, they are

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As mentioned before, chirality is one of the most critical criteria for pharmaceutical cost and pharmacologic effect of medicine which has a chiral center(s).It is well known that thalidomide tragedy revealed due to a racemic mixture of drug. Enzymes hence show up to solve this problem. Complete conversion of racemic amino acid amides to optically active amino acid derivatives was studied using lipase/Pd catalyst via dynamic kinetic resolution [64]. Authors have described that the reaction provided good yields (80–98%) and high enantiomeric excess

Savile and co-workers have reported an efficient biocatalytic process to replace a recently implemented Rh-catalyzed asymmetric enamine hydrogenation for antidiabetic compound sitagliptin. Current synthesis of sitagliptin involves enamine formation followed by asymmetric hydrogenation at high pressure using Rh-based chiral catalyst in which sitagliptin was formed in 97% ee with trace amount of Rh [65]. Savile's synthetic route showed green reaction that is direct amination of prositagliptin ketone **88** to furnish enantiopure sitagliptin **89** (99.95% ee) followed by phosphate salt formation to get sitagliptin phosphate **90** (**Scheme 27**) [65].

Ghiladi et al. have emerged a biocatalytic green process for the oxidation of pyrrole ring to provide pyrroline-2-one (**92**) [66]. Dehaloperoxidase (DHP) was supplied for biocatalytic reaction and for oxygen source, hydrogen peroxide was consumed. Finally, pyrroline-2-one was obtained with 31.7% conversion (**Scheme 28**). Authors explained that some derivatives of

Chen and co-workers experimented to improve the performance of immobilized lipase by interfacial activation on iron-oxide nanoparticles. They have tested immobilized enzyme stability and displayed that immobilized lipase exhibited much better stabilities [67]. Furthermore, with ironoxide nanoparticles, the enzyme was removed easily as mentioned in magnetic nanocatalyst.

Besides iron oxide nanoparticles, enzyme immobilization on carbon nanotubes (CNTs) and graphene is applied for many chemical reactions such as cyclization, selective amination, trans esterification, and redox reactions and biosensing applications for detection of glucose,

more powerful tools for green chemistry.

pyrrole were oxidized up to 100% conversion.

phenol, and hydrogen peroxide [62, 63].

**Scheme 26.** Resolution of racemic amino acid amides by lipase/Pd [64].

(95–98% ee) (**Scheme 26**) [64].

## thesizer which is a good tool for green chemistry.

**Scheme 25.** Synthesis of diazepine derivatives [61].

#### **3.2. Biocatalysts as a green solution**

In the literature, biocatalyst is a biological material which can be an isolated enzyme, a crude cell-free extract, an immobilized enzyme, or enzymes in whole microbial cells. Enzymes are critical endogens and have a vital role in living cells, which catalyze all the in vivo metabolic reactions to produce a necessary product for the body. To mimic the activity of enzymes for our reactions, since a century, enzymes have been utilized for the reactions in the laboratory. For many different purposes, scientists have used enzymes which are oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases. These enzymes are utilized in the industry such as food, pharmacology, medicine, and textiles. Enzymes have unique properties which can sometimes not be mimicked by artificial organic products. Enzymes show highly stereoselectivity resulting in purely one isomer and can therefore decrease the cost of medicine because chirality has a high effect on the medicine cost when candidate medicine has more than one chiral center. This chemical potential forces the chemists and medical scientists to design biocatalysts to put them into the reaction flask [62, 63].

1,2-diamino benzene (**83**), dimedone (**23**), and aromatic aldehydes (**84**) were reacted in the reaction tube in which nanocatalyst was presented. All reactions were run in microwave synBiocatalysts are biodegradable, sustainable, reusable, more efficient, and more stereoselective which means more atom economic than conventional methods. With this respect, they are more powerful tools for green chemistry.

As mentioned before, chirality is one of the most critical criteria for pharmaceutical cost and pharmacologic effect of medicine which has a chiral center(s).It is well known that thalidomide tragedy revealed due to a racemic mixture of drug. Enzymes hence show up to solve this problem. Complete conversion of racemic amino acid amides to optically active amino acid derivatives was studied using lipase/Pd catalyst via dynamic kinetic resolution [64]. Authors have described that the reaction provided good yields (80–98%) and high enantiomeric excess (95–98% ee) (**Scheme 26**) [64].

Savile and co-workers have reported an efficient biocatalytic process to replace a recently implemented Rh-catalyzed asymmetric enamine hydrogenation for antidiabetic compound sitagliptin. Current synthesis of sitagliptin involves enamine formation followed by asymmetric hydrogenation at high pressure using Rh-based chiral catalyst in which sitagliptin was formed in 97% ee with trace amount of Rh [65]. Savile's synthetic route showed green reaction that is direct amination of prositagliptin ketone **88** to furnish enantiopure sitagliptin **89** (99.95% ee) followed by phosphate salt formation to get sitagliptin phosphate **90** (**Scheme 27**) [65].

Ghiladi et al. have emerged a biocatalytic green process for the oxidation of pyrrole ring to provide pyrroline-2-one (**92**) [66]. Dehaloperoxidase (DHP) was supplied for biocatalytic reaction and for oxygen source, hydrogen peroxide was consumed. Finally, pyrroline-2-one was obtained with 31.7% conversion (**Scheme 28**). Authors explained that some derivatives of pyrrole were oxidized up to 100% conversion.

Chen and co-workers experimented to improve the performance of immobilized lipase by interfacial activation on iron-oxide nanoparticles. They have tested immobilized enzyme stability and displayed that immobilized lipase exhibited much better stabilities [67]. Furthermore, with ironoxide nanoparticles, the enzyme was removed easily as mentioned in magnetic nanocatalyst.

Besides iron oxide nanoparticles, enzyme immobilization on carbon nanotubes (CNTs) and graphene is applied for many chemical reactions such as cyclization, selective amination, trans esterification, and redox reactions and biosensing applications for detection of glucose, phenol, and hydrogen peroxide [62, 63].

**Scheme 26.** Resolution of racemic amino acid amides by lipase/Pd [64].

**Scheme 25.** Synthesis of diazepine derivatives [61].

**Scheme 24.** N-aryl-oxazolidin-2-one with nanocatalyst [58].

90 Green Chemistry

**3.2. Biocatalysts as a green solution**

thesizer which is a good tool for green chemistry.

design biocatalysts to put them into the reaction flask [62, 63].

1,2-diamino benzene (**83**), dimedone (**23**), and aromatic aldehydes (**84**) were reacted in the reaction tube in which nanocatalyst was presented. All reactions were run in microwave syn-

In the literature, biocatalyst is a biological material which can be an isolated enzyme, a crude cell-free extract, an immobilized enzyme, or enzymes in whole microbial cells. Enzymes are critical endogens and have a vital role in living cells, which catalyze all the in vivo metabolic reactions to produce a necessary product for the body. To mimic the activity of enzymes for our reactions, since a century, enzymes have been utilized for the reactions in the laboratory. For many different purposes, scientists have used enzymes which are oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases. These enzymes are utilized in the industry such as food, pharmacology, medicine, and textiles. Enzymes have unique properties which can sometimes not be mimicked by artificial organic products. Enzymes show highly stereoselectivity resulting in purely one isomer and can therefore decrease the cost of medicine because chirality has a high effect on the medicine cost when candidate medicine has more than one chiral center. This chemical potential forces the chemists and medical scientists to

**4. Case studies in green chemistry**

**95** (**Scheme 30**) [69].

(**Scheme 32**) [71].

**Scheme 30.** Green protocol for pregabalin.

In 2002, Pfizer won the U.S. Presidential Green Chemistry Award for alternative synthetic pathways for its innovative manufacturing process for sertraline hydrochloride which is the active ingredient of Zoloft that is used to treat clinical depression. Furthermore, pregabalin, sold as Lyrica, is manufactured by Pfizer for the management of neuropathic pain and epilepsy. Pfizer has designed a green route for the synthesis of pregabalin and they have reported that almost 38 million liters of alcoholic organic solvents and nearly 2000 metrics tons of raw materials were eliminated on an annual basis. Their achievements were based on biocatalyst, lipase, which was used for resolution of cyano diester

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93

GlaxoSmithKline company has announced a green reaction way for paroxetine, sold Seroxat, and Paxil, which is used for anxiety disorder. They have discussed that the yield of the overall transformation was almost double that of the process in conventional route, resulting in a greener, shorter, and more cost-efficient way. Critical step was applying of protease enzyme

Sertraline hydrochloride as known Zoloft is a selective inhibitor of serotonin reuptake which is utilized for the curing of depression [70]. When it was synthesized by conventional synthetic route, chemical reagents and metal salts were consumed. On the other hand, removing of metal salts and Pd/C catalyst gave more selective and greener protocol

Colberg and co-workers in Pfizer Global Research and Development have designed a green protocol for sertraline in which toxic solvents such as toluene, hexane were removed from

which was regioselectively hydrolyzed an ester group (**Scheme 31**) [69].

**Scheme 27.** Synthesis of sitagliptin phosphate with green chemistry.

**Scheme 28.** Oxidation of pyrrole by DHP.

Kroutil et al. reported the formation of lactam ring **94** starting from 4-oxo ester **93** in which lactate dehydrogenase, transaminase, and D-alanine were added to the reaction medium. The reaction was progressed at 30°C and 7.0 pH. Reaction was finalized to obtaining lactam derivative with 92% yield (**Scheme 29**) [68].

## **4. Case studies in green chemistry**

In 2002, Pfizer won the U.S. Presidential Green Chemistry Award for alternative synthetic pathways for its innovative manufacturing process for sertraline hydrochloride which is the active ingredient of Zoloft that is used to treat clinical depression. Furthermore, pregabalin, sold as Lyrica, is manufactured by Pfizer for the management of neuropathic pain and epilepsy. Pfizer has designed a green route for the synthesis of pregabalin and they have reported that almost 38 million liters of alcoholic organic solvents and nearly 2000 metrics tons of raw materials were eliminated on an annual basis. Their achievements were based on biocatalyst, lipase, which was used for resolution of cyano diester **95** (**Scheme 30**) [69].

GlaxoSmithKline company has announced a green reaction way for paroxetine, sold Seroxat, and Paxil, which is used for anxiety disorder. They have discussed that the yield of the overall transformation was almost double that of the process in conventional route, resulting in a greener, shorter, and more cost-efficient way. Critical step was applying of protease enzyme which was regioselectively hydrolyzed an ester group (**Scheme 31**) [69].

Sertraline hydrochloride as known Zoloft is a selective inhibitor of serotonin reuptake which is utilized for the curing of depression [70]. When it was synthesized by conventional synthetic route, chemical reagents and metal salts were consumed. On the other hand, removing of metal salts and Pd/C catalyst gave more selective and greener protocol (**Scheme 32**) [71].

Colberg and co-workers in Pfizer Global Research and Development have designed a green protocol for sertraline in which toxic solvents such as toluene, hexane were removed from

**Scheme 30.** Green protocol for pregabalin.

Kroutil et al. reported the formation of lactam ring **94** starting from 4-oxo ester **93** in which lactate dehydrogenase, transaminase, and D-alanine were added to the reaction medium. The reaction was progressed at 30°C and 7.0 pH. Reaction was finalized to obtaining lactam

derivative with 92% yield (**Scheme 29**) [68].

**Scheme 28.** Oxidation of pyrrole by DHP.

92 Green Chemistry

**Scheme 27.** Synthesis of sitagliptin phosphate with green chemistry.

**Scheme 29.** Cyclization of keto-ester to lactam by enzyme.

the strategy and comparison of solvent utilization between the first commercial route and the

The Role of Green Solvents and Catalysts at the Future of Drug Design and of Synthesis

Green chemistry is getting extended in many researches and industry areas. The reason is that the resources of the world are limited and it is necessary to be consumed with caution. On the other hand, we have already witnessed that researchers and pharmaceutical companies searched out for green protocol when manufactured the pharmaceuticals. In this spirit, most pharmaceutical companies are making increasing efforts to limit waste and avoid air and water pollution. Green solvents, nanocatalysts, and biocatalysts give many opportunities for greener methods in which impact on the environment and the cost of pharmaceuticals can be decreased. We hope that this chapter and the others give a brief consideration of importance of green chemistry. With advantages of green chemistry, hopefully, industry will alter con-

[1] Green Chemical Industry to Soar to USD 98.5 Billion by 2020, Navigant Research, Jun

[4] Sheldon RA. Catalysis: The key to waste minimization. Journal of Chemical Technology

[5] Prat D, Pardigon O, Flemming H-W, Letestu S, Ducandas V, Isnard P, Guntrum E, Senac T, Ruisseau S, Cruciani P, Hosek P. Sanofi's solvent selection guide: A step toward more sustainable processes. Organic Process Research & Development. 2013;**17**:1517-1525 [6] Prat D, Hayler J, Wells A. A survey of solvent selection guides. Green Chemistry.


http://dx.doi.org/10.5772/intechopen.71018

.HCl waste and

95

new green route showed that 76.000 L solvents, 440 tons/year of TiO2

**5. Conclusion**

**Author details**

Nurettin Menges

**References**

20, 2011

2014;**16**:4546

ventional methods with greener ones.

Address all correspondence to: nurettinmenges@yyu.edu.tr

[2] Nature Comment. Nature. Jun 2, 2016;**534**:27-29

& Biotechnology. 1997;**68**:381-388

[3] Stephen KR. C&EN Washington C&EN. Jul 4, 2016;**94**(27):22-25

Faculty of Pharmacy, Van Yuzuncu Yil University, Van, Turkey

about 40 tons of the unwanted trans isomer waste were eliminated [71].

**Scheme 31.** Formation of paroxetine through biocatalytic route.

**Scheme 32.** Green protocol for sertraline [71].

the strategy and comparison of solvent utilization between the first commercial route and the new green route showed that 76.000 L solvents, 440 tons/year of TiO2 -MeNH2 .HCl waste and about 40 tons of the unwanted trans isomer waste were eliminated [71].

#### **5. Conclusion**

Green chemistry is getting extended in many researches and industry areas. The reason is that the resources of the world are limited and it is necessary to be consumed with caution. On the other hand, we have already witnessed that researchers and pharmaceutical companies searched out for green protocol when manufactured the pharmaceuticals. In this spirit, most pharmaceutical companies are making increasing efforts to limit waste and avoid air and water pollution. Green solvents, nanocatalysts, and biocatalysts give many opportunities for greener methods in which impact on the environment and the cost of pharmaceuticals can be decreased. We hope that this chapter and the others give a brief consideration of importance of green chemistry. With advantages of green chemistry, hopefully, industry will alter conventional methods with greener ones.

#### **Author details**

Nurettin Menges

Address all correspondence to: nurettinmenges@yyu.edu.tr

Faculty of Pharmacy, Van Yuzuncu Yil University, Van, Turkey

#### **References**

**Scheme 32.** Green protocol for sertraline [71].

**Scheme 31.** Formation of paroxetine through biocatalytic route.

94 Green Chemistry


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**Chapter 6**

Provisional chapter

**Ionic Liquids as Green Corrosion Inhibitors for**

Ionic Liquids as Green Corrosion Inhibitors for Industrial

DOI: 10.5772/intechopen.70421

Present chapter describes recent advances in the field of development of ionic liquids as green and sustainable corrosion inhibitors for metals and alloys. The present chapter has been divided into several sections and subsections. Recently, development of the green and sustainable technologies for the corrosion prevention is highly desirable due to increasing ecological awareness and strict environmental regulations. In the last two decades, corrosion inhibition using ionic liquids has attracted considerable attention due to its interesting properties such as low volatility, non-inflammability, non-toxic nature, high thermal and chemical stability and high adorability. Several types of ionic liquids have been developed as "green corrosion inhibitors" for different metals and alloys such as mild steel, aluminum, copper, zinc, and magnesium in several electrolytic media. The ionic liquids are promising, noble, green and sustainable candidates to replace the

Keywords: ionic liquids, corrosion, adsorption, green corrosion inhibitors, designer

Corrosion is an irreversible and spontaneous deterioration of metal or alloy through chemical or electrochemical reaction with the environment [1, 2]. Corrosion causes enormous wastes of metallic materials which lead to enormous economic losses all over the world. Therefore, corrosion has drawn considerable academic and industrial attention [1–4]. According to highly cited study carried out by the National Association of Corrosion Engineers (NACE), in 1998,

> © The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Industrial Metals and Alloys**

Chandrabhan Verma, Eno E. Ebenso and

Chandrabhan Verma, Eno E. Ebenso and

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

traditional volatile corrosion inhibitors.

solvents, ferrous and non-ferrous metals

1.1. Corrosion and its economic impact

Mumtaz Ahmad Quraishi

Mumtaz Ahmad Quraishi

Abstract

1. Introduction

Metals and Alloys

http://dx.doi.org/10.5772/intechopen.70421

Provisional chapter

## **Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys** Ionic Liquids as Green Corrosion Inhibitors for Industrial

DOI: 10.5772/intechopen.70421

Chandrabhan Verma, Eno E. Ebenso and Mumtaz Ahmad Quraishi Chandrabhan Verma, Eno E. Ebenso and

Additional information is available at the end of the chapter Mumtaz Ahmad Quraishi

http://dx.doi.org/10.5772/intechopen.70421 Additional information is available at the end of the chapter

Metals and Alloys

#### Abstract

Present chapter describes recent advances in the field of development of ionic liquids as green and sustainable corrosion inhibitors for metals and alloys. The present chapter has been divided into several sections and subsections. Recently, development of the green and sustainable technologies for the corrosion prevention is highly desirable due to increasing ecological awareness and strict environmental regulations. In the last two decades, corrosion inhibition using ionic liquids has attracted considerable attention due to its interesting properties such as low volatility, non-inflammability, non-toxic nature, high thermal and chemical stability and high adorability. Several types of ionic liquids have been developed as "green corrosion inhibitors" for different metals and alloys such as mild steel, aluminum, copper, zinc, and magnesium in several electrolytic media. The ionic liquids are promising, noble, green and sustainable candidates to replace the traditional volatile corrosion inhibitors.

Keywords: ionic liquids, corrosion, adsorption, green corrosion inhibitors, designer solvents, ferrous and non-ferrous metals

#### 1. Introduction

#### 1.1. Corrosion and its economic impact

Corrosion is an irreversible and spontaneous deterioration of metal or alloy through chemical or electrochemical reaction with the environment [1, 2]. Corrosion causes enormous wastes of metallic materials which lead to enormous economic losses all over the world. Therefore, corrosion has drawn considerable academic and industrial attention [1–4]. According to highly cited study carried out by the National Association of Corrosion Engineers (NACE), in 1998,

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

the total annual direct cost (estimated) of corrosion in U.S.A. was US \$276 billion, equating approximately around 3.1% Gross Domestic Product (GDP; NACE 2002) [5]. In 2011, the total cost of corrosion in U.S.A. became more than US \$2.2 trillion. As for as the corrosion cost in India is concern, it was around Rs. 2 lackscrores (US \$45 billion) as proposed by 1st Global Corrosion Summit held in New Delhi, India in 2011 [6]. However, these estimated data are outdated and recently closer investigation of the NACE on the cost of corrosion is available according to which the annual global cost of corrosion is approximately US \$2.5 trillion, equating 3.4% of the global GDP [7, 8]. In India, the annual corrosion cost is more than US \$100 billion, while in South Africa, the direct corrosion cost is estimated to be around R130 billion (i.e. about US \$ 9.6 billion) [7, 8]. There are several methods of corrosion protection have been developed such as coating, anodic and cathodic protections, alloying and de-alloying and use of synthetic corrosion inhibitors by suitably applying them we can reduce this cost of corrosion from 15% (US \$375 billion) to 35% (US \$ 875 billion).

1.3. Corrosion prevention methods and corrosion inhibitors

oxygen scavengers [25–28].

Figure 1. Available methods of metallic corrosion protection.

There are several methods of corrosion protection have been developed among which, synthetic corrosion inhibitors are one of the best methods due to its advantages such as cost effectiveness and ease of application in industry [20–23]. The flow diagram of the available corrosion protection measures is shown in Figure 1. The passivating inhibitors are also known as anodic inhibitors because they general inhibit the metallic corrosion by forming the surface oxide (passive) film and causes the large anodic shift corrosion potential (Ecorr) [24]. The passivating inhibitors can be further classified into oxidizing anions that passivate the metallic surface in the absence of oxygen such as chromate, nitrite and nitrate and non-oxidizing anions that can passivate the metallic surface only in the presence of oxygen such as phosphate, tungstate and molybdate. The cathodic inhibitors either decrease the rate of cathodic reactions or precipitate on the cathodic areas to increase the surface impedance that decrease the diffusion of reducible species to these areas [24]. The cathodic inhibitors act by three different mechanisms namely, cathodic poisons, cathodic precipitates and oxygen scavengers. Generally, arsenic and antimony make the association of hydrogen more difficult and act as cathodic poisons, calcium, zinc and magnesium precipitates in their oxide forms and act as cathodic precipitates and sodium sulfite and hydrazine react with surrounding oxygen and act as

Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys

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#### 1.2. Causes of corrosion

Pure metals are chemically unstable and undergo chemical and/or electrochemical reactions with their environments to form more stable oxides. The chemical reactivity of pure metals is related to their natural tendency of oxidation (except gold, silver and platinum), as they have tendency to return their natural state by chemical reactions with the constituents of environment [9–12]. Since corrosion is a spontaneous process, relative rate of corrosion among a given series of metals is related to the change in standard Gibb's free energy (ΔGᴼ). As more negative value of ΔGᴼ as high spontaneity of reaction and consequently higher corrosion rate [9–12]. When metals and alloys exposed to environment and particularly in acid solution during several industrial processes like acid pickling, acid descaling, etc., corrosion will undergo forming stable oxides [13–15]. Therefore, these processes required some additives known as corrosion inhibitors that form protective covering over the metallic surface and isolate metals from the environment and thereby inhibit the corrosive degradation [13–17]. The corrosion products such as rust and scale can also act as corrosion inhibitors by accumulation on the surface and act as physical protective barrier. The natural tendency of metallic corrosion can be affected by several factors, however, the relative rate of corrosion of any particular metal is depending upon the Pilling—Bedworth ratio which is defined as Md/nmD, where m and d are the atomic weight and density of the metal, respectively and M and D are the molecular weight and density of scale (corrosion product) accumulated on the metallic surface, and n denotes the number of metallic atoms in the molecular formula of corrosion product (rust or scale); for example for Fe2O3 and Al2O3, n = 2 [18, 19]. The magnitude of Pilling – Bedworth ratio can be used to explain where the surface film will be protective or not. The volume of corrosion product will be small than the volume of metal from which it was formed for Md/nmD < 1, in this situation it is expected that surface film of corrosion product contains pores and cracks that would be relatively non-protective. On the other hand, volume of corrosion product will be larger than the volume of metal for Md/ nmD > 1, in that situation it is expected that surface film of corrosion product is relatively more compressed and compact and consequently the metal would be relatively more protected.

#### 1.3. Corrosion prevention methods and corrosion inhibitors

the total annual direct cost (estimated) of corrosion in U.S.A. was US \$276 billion, equating approximately around 3.1% Gross Domestic Product (GDP; NACE 2002) [5]. In 2011, the total cost of corrosion in U.S.A. became more than US \$2.2 trillion. As for as the corrosion cost in India is concern, it was around Rs. 2 lackscrores (US \$45 billion) as proposed by 1st Global Corrosion Summit held in New Delhi, India in 2011 [6]. However, these estimated data are outdated and recently closer investigation of the NACE on the cost of corrosion is available according to which the annual global cost of corrosion is approximately US \$2.5 trillion, equating 3.4% of the global GDP [7, 8]. In India, the annual corrosion cost is more than US \$100 billion, while in South Africa, the direct corrosion cost is estimated to be around R130 billion (i.e. about US \$ 9.6 billion) [7, 8]. There are several methods of corrosion protection have been developed such as coating, anodic and cathodic protections, alloying and de-alloying and use of synthetic corrosion inhibitors by suitably applying them we can reduce this cost of

Pure metals are chemically unstable and undergo chemical and/or electrochemical reactions with their environments to form more stable oxides. The chemical reactivity of pure metals is related to their natural tendency of oxidation (except gold, silver and platinum), as they have tendency to return their natural state by chemical reactions with the constituents of environment [9–12]. Since corrosion is a spontaneous process, relative rate of corrosion among a given series of metals is related to the change in standard Gibb's free energy (ΔGᴼ). As more negative value of ΔGᴼ as high spontaneity of reaction and consequently higher corrosion rate [9–12]. When metals and alloys exposed to environment and particularly in acid solution during several industrial processes like acid pickling, acid descaling, etc., corrosion will undergo forming stable oxides [13–15]. Therefore, these processes required some additives known as corrosion inhibitors that form protective covering over the metallic surface and isolate metals from the environment and thereby inhibit the corrosive degradation [13–17]. The corrosion products such as rust and scale can also act as corrosion inhibitors by accumulation on the surface and act as physical protective barrier. The natural tendency of metallic corrosion can be affected by several factors, however, the relative rate of corrosion of any particular metal is depending upon the Pilling—Bedworth ratio which is defined as Md/nmD, where m and d are the atomic weight and density of the metal, respectively and M and D are the molecular weight and density of scale (corrosion product) accumulated on the metallic surface, and n denotes the number of metallic atoms in the molecular formula of corrosion product (rust or scale); for example for Fe2O3 and Al2O3, n = 2 [18, 19]. The magnitude of Pilling – Bedworth ratio can be used to explain where the surface film will be protective or not. The volume of corrosion product will be small than the volume of metal from which it was formed for Md/nmD < 1, in this situation it is expected that surface film of corrosion product contains pores and cracks that would be relatively non-protective. On the other hand, volume of corrosion product will be larger than the volume of metal for Md/ nmD > 1, in that situation it is expected that surface film of corrosion product is relatively more compressed and compact and consequently the metal would be relatively more

corrosion from 15% (US \$375 billion) to 35% (US \$ 875 billion).

1.2. Causes of corrosion

104 Green Chemistry

protected.

There are several methods of corrosion protection have been developed among which, synthetic corrosion inhibitors are one of the best methods due to its advantages such as cost effectiveness and ease of application in industry [20–23]. The flow diagram of the available corrosion protection measures is shown in Figure 1. The passivating inhibitors are also known as anodic inhibitors because they general inhibit the metallic corrosion by forming the surface oxide (passive) film and causes the large anodic shift corrosion potential (Ecorr) [24]. The passivating inhibitors can be further classified into oxidizing anions that passivate the metallic surface in the absence of oxygen such as chromate, nitrite and nitrate and non-oxidizing anions that can passivate the metallic surface only in the presence of oxygen such as phosphate, tungstate and molybdate. The cathodic inhibitors either decrease the rate of cathodic reactions or precipitate on the cathodic areas to increase the surface impedance that decrease the diffusion of reducible species to these areas [24]. The cathodic inhibitors act by three different mechanisms namely, cathodic poisons, cathodic precipitates and oxygen scavengers. Generally, arsenic and antimony make the association of hydrogen more difficult and act as cathodic poisons, calcium, zinc and magnesium precipitates in their oxide forms and act as cathodic precipitates and sodium sulfite and hydrazine react with surrounding oxygen and act as oxygen scavengers [25–28].

Figure 1. Available methods of metallic corrosion protection.

Organic compounds are also known as filming inhibitors; generally inhibit metallic corrosion by forming the protective surface film that isolates the metal form the surrounding (corrosive) environments. Most of the well know organic inhibitors are heterocyclic compounds containing polar functional groups such as -NO2, -OH, -OCH3, -CH3, -NH2, -COOC2H5, -CONH2, -COOH, etc. [29–31]. These polar functional groups and conjugated π-electrons of multiple bonds (double and triple) act as adsorption centers during metal-inhibitor interactions. This type of adsorption results into blocking of anodic and cathodic reactions indirectly. The adsorption of these inhibitors is affected by several factors such as nature and magnitude of charge present on metal, nature of electrolyte, electronic structure of inhibitor molecules, nature of substituents, solution temperature, exposure time etc. [29–34].

1.4.1. Properties and applications of ionic liquids

etc. (Figure 2) [55–62].

Figure 2. Applications of ionic liquids.

The ionic liquids have several fascinating properties such as low volatility (low vapour pressure), very high stability over wide range of pH and temperature, capability to dissolve a wide range of organic and inorganic compounds as they generally exist in their ionic forms through which they easily dissolve in polar solvents like H2O, HCl, etc., moreover, their cationic counterparts generally contain large organic moieties through which they are capable to dissolve non-polar organic compounds, capability to solubilize gases like H2, CO, CO2 etc., dependency of solubility on the nature of cations and anions, acceleration of reaction rate for chemical transformation under microwave heating, long time stability without decomposition and their high selectivity [55–62]. These fascinating properties of ionic liquids make them good candidature to replace conventional organic volatile solvents with non-conventional ionic liquids that have been employed in variety of chemical transformations such as solvents for synthesis of nanomaterials and nanostructure, biochemical transformations, nucleophilic substitution reactions, electrodeposition of metals and semiconductors and solvent extraction, separation of petrochemical relevance mobile phase converter in HPLC, catalyst in various chemical and biochemical transformations, dye sensitizer for solar cells, oil shale processing,

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#### 1.4. Ionic liquids as green corrosion inhibitors

"Green chemistry" which is a relatively new and rapidly growing area of chemistry that involves designing of products and processes that reduce the use and production of toxic substances [35– 38]. Recently, worldwide growing ecological awareness and strict environmental protocols do not permit the synthesis and utilization of hazardous traditional volatile corrosion inhibitors. Therefore, there is vital need for improvement in the synthetic and engineering chemistry either by environmental friendly starting materials or proper designing for synthesis using nonclassical energy sources such as ultrasound and microwave heating. In this regard use of multi component reactions (MCRs) in combination with ultrasonic (sonochemical) and microwave irradiation is one of the best alternative synthetic strategies toward "green synthesis." Recently, scientists are trying to develop plant extracts and drugs as green corrosion inhibitors due to their natural and/or biological origins and non-toxic nature [39–41]. However, extraction and purification of plant extracts is very tedious, laborious, extremely expensive, time consuming and requires large amount of organic solvents [42, 43]. Therefore, there is need to develop "green inhibitors" by proper designing of the synthesis that can be achieved either by using cheap and environmental friendly starting materials or by synthesizing them from one step MCR reactions.

Toward, "green chemistry," utilization of ionic liquids has immersed as new strategy due to its several fascinating properties such as low melting point (lower that 100C), high polarity, low toxicity, low vapor pressure, very high thermal and chemical stability, less hazardous influence on environment and living being [44–48]. By definition, ionic liquids are materials that mainly composed of ions with melting point below than 100C. The properties of ionic liquids could be modified according to the need by proper selection of cations and anions, which is the greatest advantage for designing ionic liquids of specific properties [49–51]. Due to this reason ionic liquids are also known as "designer chemicals" that have potential to consume as solvent or catalysis for various chemical transformations [44–51]. The rapid utilization of ionic liquids in almost all fields of chemistry and chemical engineering is resulted to their above mentioned fascinating properties which enable them as "green and sustainable chemicals" having tendency to dissolve wide range of inorganic and organic compounds. The ionic liquids follow the principals of "green chemistry" proposed by Paul Anastas and John Warner [52–54].

#### 1.4.1. Properties and applications of ionic liquids

Organic compounds are also known as filming inhibitors; generally inhibit metallic corrosion by forming the protective surface film that isolates the metal form the surrounding (corrosive) environments. Most of the well know organic inhibitors are heterocyclic compounds containing polar functional groups such as -NO2, -OH, -OCH3, -CH3, -NH2, -COOC2H5, -CONH2, -COOH, etc. [29–31]. These polar functional groups and conjugated π-electrons of multiple bonds (double and triple) act as adsorption centers during metal-inhibitor interactions. This type of adsorption results into blocking of anodic and cathodic reactions indirectly. The adsorption of these inhibitors is affected by several factors such as nature and magnitude of charge present on metal, nature of electrolyte, electronic structure of inhibitor molecules, nature of

"Green chemistry" which is a relatively new and rapidly growing area of chemistry that involves designing of products and processes that reduce the use and production of toxic substances [35– 38]. Recently, worldwide growing ecological awareness and strict environmental protocols do not permit the synthesis and utilization of hazardous traditional volatile corrosion inhibitors. Therefore, there is vital need for improvement in the synthetic and engineering chemistry either by environmental friendly starting materials or proper designing for synthesis using nonclassical energy sources such as ultrasound and microwave heating. In this regard use of multi component reactions (MCRs) in combination with ultrasonic (sonochemical) and microwave irradiation is one of the best alternative synthetic strategies toward "green synthesis." Recently, scientists are trying to develop plant extracts and drugs as green corrosion inhibitors due to their natural and/or biological origins and non-toxic nature [39–41]. However, extraction and purification of plant extracts is very tedious, laborious, extremely expensive, time consuming and requires large amount of organic solvents [42, 43]. Therefore, there is need to develop "green inhibitors" by proper designing of the synthesis that can be achieved either by using cheap and environmental friendly starting materials or by synthesizing them from one step MCR reactions. Toward, "green chemistry," utilization of ionic liquids has immersed as new strategy due to its several fascinating properties such as low melting point (lower that 100C), high polarity, low toxicity, low vapor pressure, very high thermal and chemical stability, less hazardous influence on environment and living being [44–48]. By definition, ionic liquids are materials that mainly composed of ions with melting point below than 100C. The properties of ionic liquids could be modified according to the need by proper selection of cations and anions, which is the greatest advantage for designing ionic liquids of specific properties [49–51]. Due to this reason ionic liquids are also known as "designer chemicals" that have potential to consume as solvent or catalysis for various chemical transformations [44–51]. The rapid utilization of ionic liquids in almost all fields of chemistry and chemical engineering is resulted to their above mentioned fascinating properties which enable them as "green and sustainable chemicals" having tendency to dissolve wide range of inorganic and organic compounds. The ionic liquids follow the principals of "green chemistry" proposed by Paul

substituents, solution temperature, exposure time etc. [29–34].

1.4. Ionic liquids as green corrosion inhibitors

106 Green Chemistry

Anastas and John Warner [52–54].

The ionic liquids have several fascinating properties such as low volatility (low vapour pressure), very high stability over wide range of pH and temperature, capability to dissolve a wide range of organic and inorganic compounds as they generally exist in their ionic forms through which they easily dissolve in polar solvents like H2O, HCl, etc., moreover, their cationic counterparts generally contain large organic moieties through which they are capable to dissolve non-polar organic compounds, capability to solubilize gases like H2, CO, CO2 etc., dependency of solubility on the nature of cations and anions, acceleration of reaction rate for chemical transformation under microwave heating, long time stability without decomposition and their high selectivity [55–62]. These fascinating properties of ionic liquids make them good candidature to replace conventional organic volatile solvents with non-conventional ionic liquids that have been employed in variety of chemical transformations such as solvents for synthesis of nanomaterials and nanostructure, biochemical transformations, nucleophilic substitution reactions, electrodeposition of metals and semiconductors and solvent extraction, separation of petrochemical relevance mobile phase converter in HPLC, catalyst in various chemical and biochemical transformations, dye sensitizer for solar cells, oil shale processing, etc. (Figure 2) [55–62].

Figure 2. Applications of ionic liquids.

#### 1.4.2. Classification of ionic liquids

The ionic liquids can be classified into several categories based on various bases. Hajipour and Refiee [63] have classified the ionic liquids into eleven classes namely, neutral ionic liquids, acid ionic liquids, basic ionic liquids, ionic liquids with amphoteric anions, functionalized ionic liquids, protic ionic liquids, chiral ionic liquids, supported ionic liquids, bio-ionic liquids, poly-ionic liquids, and energetic ionic liquids and also have described common features and properties of these ionic liquids. However, Suresh and Sandhu [62, 63] classified ionic liquids into only two classes namely, cationic and anionic ionic liquids. They were further subdivided anionic ionic liquids into several subclasses namely, borates, dicyanamide (DCN), Halide, Bis(trifluoromethylsulfonyl)imide (NTF), nonaflate (NON), phosphate, sulfate, sulfonate, thiocyanate (SCN), tricyanomethide (TCC) based anionic liquids. Some common classes of ionic liquids with examples and their salient features are described in Table 1.

1.5. Comparison between organic inhibitors and ionic liquids

2. Applications of ionic liquids as corrosion inhibitors

2.1. Ionic liquids as corrosion inhibitors for mild steel

Several fascinating properties of the ionic liquids make them ideal candidates to replace the traditional corrosion inhibitors that have several adverse effects on environment and living beings. Recently, a large number of works have been reported describing the use of ionic

Mild steel is most frequently used as constructional material for several industries due to its high mechanical strength and low cost [74, 75]. However, these materials are highly reactive and undergo corrosive degradation during various industrial processes like acid cleaning, acid descaling, acid etching, and acid pickling processes that require use of additives in order to increase the lifespan of metal/alloy has used [76]. The use of organic compounds containing heterocyclic rings and polar fictional groups such as amino, hydroxyl, methyl, methoxy, nitro, nitrile, etc., as additive is one of the most important alterative to protect metals and alloys from these unsolicited reactions [74, 75]. These compounds inhibit corrosion by adsorbing over the metallic surface [74–77]. However, the use of these highly volatile traditional toxic corrosion

"green and sustainable" nature.

liquids as corrosion inhibitors.

Over past two decades corrosion inhibition using ionic liquids (ILs) has experienced an outstanding growth and abundant examples on corrosion inhibitions are available that have been effectively carried out in different corrosive media. Although, traditional volatile compounds have been most extensively used as corrosion inhibitors in several industries. However, most of them are toxic for living being and environment [64–66]. In view of this, ionic liquids (ILs) have been used extensively in recent years. Ionic liquids have several advantageous physiochemical properties including non-toxic, high conductivity, non-flammability, as well as high thermal and chemical stability [35–63]. One of the most significant characteristics of ionic liquids is their environmental friendly and non-hazardous nature due to their nonnegligible vapour pressure. Unlike to traditional volatile corrosion inhibitors, due to their extremely low vapour pressure these compounds will not evaporate and will not contaminate the surrounding environment [67, 68]. Additionally, sometimes the use of organic inhibitors particularly polymeric and high molecular weighted organic compounds is limited due to their extremely low solubility in the polar corrosive media [69–72]. However, ionic liquids are highly soluble in the polar corrosive environments due to their ionic nature [73]. Furthermore, there is limit less prospect of suitably modifying the structure of the anion and cation of any given ionic liquids delivers an unlimited amount of potential derivatives having numerous physiochemical properties, while this type of modification is not possible with volatile corrosion inhibitors. In summary, the use of ionic liquids as corrosion inhibitors is preferred as compared to traditional volatile (toxic) corrosion inhibitors due to their several advantageous physiochemical properties including their high solubility, non-toxic, high conductivity, nonflammability, less volatility as well as high chemical stability and more importantly due to their

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Table 1. Classification of ionic liquids and their common features.

#### 1.5. Comparison between organic inhibitors and ionic liquids

1.4.2. Classification of ionic liquids

108 Green Chemistry

described in Table 1.

1 Neutral ionic liquids

2 Acidic ionic liquids

5 Supported ionic liquids

The ionic liquids can be classified into several categories based on various bases. Hajipour and Refiee [63] have classified the ionic liquids into eleven classes namely, neutral ionic liquids, acid ionic liquids, basic ionic liquids, ionic liquids with amphoteric anions, functionalized ionic liquids, protic ionic liquids, chiral ionic liquids, supported ionic liquids, bio-ionic liquids, poly-ionic liquids, and energetic ionic liquids and also have described common features and properties of these ionic liquids. However, Suresh and Sandhu [62, 63] classified ionic liquids into only two classes namely, cationic and anionic ionic liquids. They were further subdivided anionic ionic liquids into several subclasses namely, borates, dicyanamide (DCN), Halide, Bis(trifluoromethylsulfonyl)imide (NTF), nonaflate (NON), phosphate, sulfate, sulfonate, thiocyanate (SCN), tricyanomethide (TCC) based anionic liquids. Some common classes of ionic liquids with examples and their salient features are

,

Anions are associated with cations with weal electrostatic interaction, low melting point, low viscosity, used as inert solvent, good thermal and electrochemical stability

Ionic liquids with acidic cations or acidic anion, enhanced solubility in water, possess good catalytic

nature due to presence of one or more amine group (1<sup>ᴼ</sup>

bound functional group on the

cation and/or anion

, 2<sup>ᴼ</sup> or 3<sup>ᴼ</sup>

efficiency

amine)

, ,

,

, Anions= (HSO4

3 Basic ionic liquids These ionic liquids are basic in

4 Functionalized ionic liquids Ionic liquids that has a covalently

,


SN Types of ionic liquids (classes) Some typical examples Remark

Al)

Table 1. Classification of ionic liquids and their common features.

Over past two decades corrosion inhibition using ionic liquids (ILs) has experienced an outstanding growth and abundant examples on corrosion inhibitions are available that have been effectively carried out in different corrosive media. Although, traditional volatile compounds have been most extensively used as corrosion inhibitors in several industries. However, most of them are toxic for living being and environment [64–66]. In view of this, ionic liquids (ILs) have been used extensively in recent years. Ionic liquids have several advantageous physiochemical properties including non-toxic, high conductivity, non-flammability, as well as high thermal and chemical stability [35–63]. One of the most significant characteristics of ionic liquids is their environmental friendly and non-hazardous nature due to their nonnegligible vapour pressure. Unlike to traditional volatile corrosion inhibitors, due to their extremely low vapour pressure these compounds will not evaporate and will not contaminate the surrounding environment [67, 68]. Additionally, sometimes the use of organic inhibitors particularly polymeric and high molecular weighted organic compounds is limited due to their extremely low solubility in the polar corrosive media [69–72]. However, ionic liquids are highly soluble in the polar corrosive environments due to their ionic nature [73]. Furthermore, there is limit less prospect of suitably modifying the structure of the anion and cation of any given ionic liquids delivers an unlimited amount of potential derivatives having numerous physiochemical properties, while this type of modification is not possible with volatile corrosion inhibitors. In summary, the use of ionic liquids as corrosion inhibitors is preferred as compared to traditional volatile (toxic) corrosion inhibitors due to their several advantageous physiochemical properties including their high solubility, non-toxic, high conductivity, nonflammability, less volatility as well as high chemical stability and more importantly due to their "green and sustainable" nature.

#### 2. Applications of ionic liquids as corrosion inhibitors

Several fascinating properties of the ionic liquids make them ideal candidates to replace the traditional corrosion inhibitors that have several adverse effects on environment and living beings. Recently, a large number of works have been reported describing the use of ionic liquids as corrosion inhibitors.

#### 2.1. Ionic liquids as corrosion inhibitors for mild steel

Mild steel is most frequently used as constructional material for several industries due to its high mechanical strength and low cost [74, 75]. However, these materials are highly reactive and undergo corrosive degradation during various industrial processes like acid cleaning, acid descaling, acid etching, and acid pickling processes that require use of additives in order to increase the lifespan of metal/alloy has used [76]. The use of organic compounds containing heterocyclic rings and polar fictional groups such as amino, hydroxyl, methyl, methoxy, nitro, nitrile, etc., as additive is one of the most important alterative to protect metals and alloys from these unsolicited reactions [74, 75]. These compounds inhibit corrosion by adsorbing over the metallic surface [74–77]. However, the use of these highly volatile traditional toxic corrosion inhibitors is limited due to increasing ecological awareness and strict environmental regulations. In this regards consumption of "ionic liquids" as corrosion inhibitors has become an important green alternative methods of corrosion protection. Literature survey reveals that several synthetic ionic liquids have been used as effective corrosion inhibitors for mild steel (or carbon steel) in various electrolytic media. Likhanova et al. [78] synthesized two ionic liquids namely, 1,3 dioctadecylimidazolium bromide (ImDC18Br) and N-Octadecylpyridiniumbromide (PyC18Br) using conventional and microwave heating methods, respectively and investigated their inhibition performance on mild steel corrosion in 1M H2SO4 using several experimental techniques. They were observed that studied ionic liquids acted as good corrosion inhibitors for mild steel in aqueous acid solution. The adsorption on metallic surface takes place via chemisorption mechanism which obeyed the Langmuir adsorption isotherm. Potentiodynamic polarization results revealed that applied ionic liquids behaved as mixed type inhibitors. These authors were proposed a mechanism of corrosion inhibition on the basis of results obtained from SEM-EDX, XRD and Mossbauer analyses. The inhibition performance of the 1-ethyl-3-methylimidazolium dicyanamide (EMID) on mild steel corrosion in 0.1M H2SO4 using several experimental techniques [79] has been tested. Results showed that EMID inhabits metallic corrosion by adsorption on the metallic surface which was confirmed by decreased values of Cdl and increased surface coverage in presence of the inhibitor. The adsorption of the EMID over metallic surface obeyed the Langmuir adsorption isotherm. The inhibition performance of two ionic liquids namely 1 butyl-3-methylimidazolium chlorides (BMIC) and 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4) on mild steel corrosion in 1M HCl have been studied by Zhang and Hua [80] using electrochemical and weight loss experiments. Results showed that the inhibition efficiency of both ionic liquids obeyed the order: ([BMIM]HSO4) > (BMIC). They were found that adsorption of these compounds on mild steel surface obeyed the Langmuir adsorption isotherm. Potentiodynamic study suggested that both ionic liquids acted as mixed type inhibitors. The effect of temperature (303–333 K) was also investigated on both the ionic liquids. Finally, several activation and thermodynamic parameters such as energy of activation (Ea), enthalpy of activation (ΔH), entropy of activation (ΔS), adsorption constant (Kads) and Gibb's standard free energy (ΔG<sup>ᴼ</sup> ) were calculated in order to explain the mechanism of adsorption and corrosion inhibition of both the ionic liquids.

The inhibition performance of 1-octyl-3-methylimidazolium bromide ([OMIM]Br) and 1-allyl-3-octylimidazolium bromide ([AOIM]Br) on mild steel corrosion in 0.5 M H2SO4 using weight loss, electrochemical, scanning electron microscopy (SEM) and Quantum chemical calculations techniques showed that both the ionic liquids acted as good corrosion inhibitors and their adsorption on the metallic surface obeyed the El-Awady thermodynamic–kinetic model and acted as slightly cathodic type inhibitors [81].

Table 2 represents the corrosion inhibition properties of several other ionic liquids that have been employed as inhibitors for mild steel corrosion in electrolytic media [82–116]. The chitosan-based ionic liquid was synthesized using oleic acid and p-toluene sulfonic acid and its corrosion inhibition efficiency was determined using several electrochemical measurements [117]. Results of the investigated study revealed that presence of the ionic liquid in the chloride containing corrosive medium decreased the rate of metallic dissolution as well as hydrogen evolution. Adsorption of the ionic liquid followed the Langmuir adsorption Synthetic scheme and/or chemical structure of

Techniques Electrochemical

microscopy

Experimental,

Monte Carlo simulation

 quantum chemical,

Langmuir adsorption

type

 isotherm, mixed

1M HCl

[83, 84]

> ,

]−, [BDMIM]+[BF4]

(CPEPB)

(G2IL): n = 2; (G3IL): n = 3; (G6IL): n = 6

Scheme 2 ,

(CTAB) (SDS)

Electrochemical,

calculations

 (DFT)

Electrochemical,

microscopy

 Scanning electron

Flory–Huggins

mixed type

 adsorption

 isotherm,

3.5% NaCl

[88]

111

http://dx.doi.org/10.5772/intechopen.70421

 Quantum chemical

Langmuir adsorption

type

 isotherm, mixed

1M HCl

[87]

Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys

Scheme 1

Gravimetric,

electrochemical

Langmuir adsorption

type

 isotherm, mixed

1M HCl

[86]

−, [C10MIM]+[BF4]−

Gravimetric,

chemical calculations

electrochemical,

 quantum

Langmuir adsorption

type

 isotherm, mixed

1M HCl

[85]

[EMIM]+[BF4

,

 and scanning electron

Langmuir adsorption

type

 isotherm, mixed

3.5% NaCl

[82]

Nature of adsorption

Electrolytic

 media

 Ref.

> ionic liquids


inhibitors is limited due to increasing ecological awareness and strict environmental regulations.

green alternative methods of corrosion protection. Literature survey reveals that several synthetic ionic liquids have been used as effective corrosion inhibitors for mild steel (or carbon steel) in various electrolytic media. Likhanova et al. [78] synthesized two ionic liquids namely, 1,3 dioctadecylimidazolium bromide (ImDC18Br) and N-Octadecylpyridiniumbromide (PyC18Br) using conventional and microwave heating methods, respectively and investigated their inhibition performance on mild steel corrosion in 1M H2SO4 using several experimental techniques. They were observed that studied ionic liquids acted as good corrosion inhibitors for mild steel in aqueous acid solution. The adsorption on metallic surface takes place via chemisorption mechanism which obeyed the Langmuir adsorption isotherm. Potentiodynamic polarization results revealed that applied ionic liquids behaved as mixed type inhibitors. These authors were proposed a mechanism of corrosion inhibition on the basis of results obtained from SEM-EDX, XRD and Mossbauer analyses. The inhibition performance of the 1-ethyl-3-methylimidazolium

niques [79] has been tested. Results showed that EMID inhabits metallic corrosion by adsorption

coverage in presence of the inhibitor. The adsorption of the EMID over metallic surface obeyed the Langmuir adsorption isotherm. The inhibition performance of two ionic liquids namely 1 butyl-3-methylimidazolium chlorides (BMIC) and 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4) on mild steel corrosion in 1M HCl have been studied by Zhang and Hua [80] using electrochemical and weight loss experiments. Results showed that the inhibition efficiency

tion of these compounds on mild steel surface obeyed the Langmuir adsorption isotherm. Potentiodynamic study suggested that both ionic liquids acted as mixed type inhibitors. The

tion (ΔH), entropy of activation (ΔS), adsorption constant (Kads) and Gibb's standard free energy

The inhibition performance of 1-octyl-3-methylimidazolium bromide ([OMIM]Br) and 1-allyl-3-octylimidazolium bromide ([AOIM]Br) on mild steel corrosion in 0.5 M H2SO4 using weight loss, electrochemical, scanning electron microscopy (SEM) and Quantum chemical calculations techniques showed that both the ionic liquids acted as good corrosion inhibitors and their

Table 2 represents the corrosion inhibition properties of several other ionic liquids that have

chitosan-based ionic liquid was synthesized using oleic acid and p-toluene sulfonic acid and its corrosion inhibition efficiency was determined using several electrochemical measurements [117]. Results of the investigated study revealed that presence of the ionic liquid in the chloride containing corrosive medium decreased the rate of metallic dissolution as well as hydrogen evolution. Adsorption of the ionic liquid followed the Langmuir adsorption

been employed as inhibitors for mild steel corrosion in electrolytic media [82

) were calculated in order to explain the mechanism of adsorption and corrosion inhibition

2SO

–333 K) was also investigated on both the ionic liquids. Finally, several

" as corrosion inhibitors has become an important

<sup>4</sup> using several experimental tech-

4) > (BMIC). They were found that adsorp-

E

Cdl and increased surface

a), enthalpy of activa-

–kinetic model and

–116]. The

"ionic liquids

dicyanamide (EMID) on mild steel corrosion in 0.1M H

of both ionic liquids obeyed the order: ([BMIM]HSO

acted as slightly cathodic type inhibitors [81].

effect of temperature (303

of both the ionic liquids.

(ΔG<sup>ᴼ</sup>

on the metallic surface which was confirmed by decreased values of

activation and thermodynamic parameters such as energy of activation (

adsorption on the metallic surface obeyed the El-Awady thermodynamic

In this regards consumption of

110 Green Chemistry

Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys http://dx.doi.org/10.5772/intechopen.70421 111


Techniques Gravimetric,

electrochemical,

 SEM

 Langmuir adsorption

 isotherm

1M H2SO4

[96]

Nature of adsorption

Electrolytic

 media

 Ref.

> ionic liquids

,

([BsMIM]-[HSO4]) ([BsMIM][BF4]),

Weight loss and polarization

Langmuir adsorption

 isotherm, mixed

 Production

 water

 [97]

techniques

Electrochemical

 techniques

–

CO2

[98]

, ,

[EMIM][BF4], [BMIM][Otf], [EMIM][Otf]

Electrochemical),

scattering (DLS), FT-IR and DFT

 AFM, dynamic light

Langmuir adsorption

type

 isotherm, mixed

2 M HCl

[99]

, , , , ,

(EMIm Cl), (BMIm Cl), (BMIm PF6), (BMIm BF4), (BMIm

Br), (HMIm Cl)

Electrochemical,

techniques

Electrochemical

measurements

mixed type

Flory-Huggins

 adsorption

 isotherm,

2M H2SO4

[101]

113

http://dx.doi.org/10.5772/intechopen.70421

 surface analysis

–

NaCl (pH 3.8 and pH

[100]

Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys

6.8)

(DMICL)

,

(MTABr)

(TOMABr)

112 Green Chemistry


Techniques Weight loss,

AFM, contact angle method

Weight loss,

DFT methods

Weight loss,

electrochemical

Langmuir adsorption

type

 isotherm, mixed

1M HCl

[91, 92]

electrochemical,

 SEM,

–

Open and controlled

[90]

environments

electrochemical,

 SEM,

Langmuir adsorption

type

 isotherm, mixed

1M HCl

[89]

Nature of adsorption

Electrolytic

 media

 Ref.

112 Green Chemistry

ionic liquids (TSIL)

([C4C1im][FeCl4])

[BMIM]Br

,

Electrochemical,

 SEM

Langmuir adsorption

type

 isotherm, mixed

1M HCl, 1M H2SO4

[93]

(DBImL) (DBImA)

Electrochemical,

DFT, QSAR and Monte Carlo

simulation

spectroscopic,

 SEM,

Langmuir adsorption

type

 isotherm, mixed

1M HCl,

[94]

, , , ,

, [EMIM] + [Ac] −, [BMIM] + [SCN]

[EMIM] + [EtSO4

 ] - −, [BMIM] + [Ac] −, [BMIM] + [DCA] −

Electrochemical,

 Immersion,

 SEM

–

0.01M NaCl

[95]

Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys http://dx.doi.org/10.5772/intechopen.70421 113

,

(MTABr)

(TOMABr)


R= IL1:C H4 9; IL2:C H8

C22H45

Synthetic scheme and/or chemical structure of

Techniques Weight loss,

electrochemical,

 SEM

 Langmuir isotherm, mixed type

Nature of adsorption

Electrolytic

1M H2SO4

[107]

 media

 Ref.

> ionic liquids

,

(DDI), (TMA) (TML)

R= -CH3 (I); -C H4 8 (II); -C H8 9 (III)

,

[HMIM][TfO] [HMIM][BF4],

,

[HMIM][PF6] [HMIM][I]

,

Weight loss,

Weight loss,

electrochemical

Langmuir adsorption

type

 isotherm, mixed

2M H2SO4 and 3.5%

[111]

http://dx.doi.org/10.5772/intechopen.70421

115

NaCl

electrochemical

–

Arabian Gulf Sea-

[110]

Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys

water

([EMIm]Cl) ([Py1,4]Cl)

(BMIC)

,

Electrochemical

Electrochemical,

analyses, quantum chemical

calculations

spectroscopic

Langmuir isotherm, mixed type

1M HCl

[109]

 polarization

 test, SEM –

Ethanol solution

 [108]

17; IL3:C12H25; IL4:C18H37; IL5:

114 Green Chemistry


Techniques Weight loss,

measurements,

chemical calculations

 QSAR, quantum

electrochemical

Langmuir adsorption

type

 isotherm, mixed

1M HCl

[102]

Nature of adsorption

Electrolytic

 media

 Ref.

114 Green Chemistry

ionic liquids

, , [emim][tosylate])

, [emim]-[Otf], [emim]-[DCA], [emim][acetate],

,

Electrochemical

 and surface analysis

 Flory  mixed type

Hugginsadsortion

 isotherm,

2 M HCl

[104]

(CTAB ) (SDS)

Weight loss,

quantum chemical calculation

> R= IL1:C H4 9; IL2:C H8

Scheme 5

Weight loss,

AFm

electrochemical,

 SEM,

Langmuir isotherm, mixed type but IL3

1M H2SO4

[106]

behave as cathodic type

C22H45

17; IL3:C12H25; IL4:C18H37; IL5:

electrochemical,

 SEM, and

Flory 

Huggins isotherm, mixed type

 0.5 M H2SO4

[105]

,,

,

,

Electrochemical

–

CO2 capture system

 [103] Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys http://dx.doi.org/10.5772/intechopen.70421 115


Techniques Electrochemical,

analysis methods

 Quantum, surface

Mixed type

Nature of adsorption

Electrolytic

1M HCl

[121]

 media

 Ref.

> ionic liquids

(EOPC)

(*VImC4PF6*) (*VImC8PF6*)

(*VImC12PF6*) (*VImC18PF6*)

(*VImC22PF6*)

Table 2. Ionic liquids as corrosion inhibitors for mild steel in different electrolytic

performance.

 media, their mode of adsorption

 and techniques

 used for evaluation

 of the inhibition

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117

Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys

Weight loss,

Weight loss and

polarization

 methods

electrochemical

Langmuir adsorption

type

 isotherm, mixed

1M H2SO4

[123]

electrochemical

 methods

 Langmuir adsorption

type

 isotherm, mixed

0.5M H2SO4

[122]

116 Green Chemistry

Techniques Potentiodynamic

polarization

 and weight loss

polarization,

 linear

Langmuir adsorption

type

 isotherm, mixed

1M HCl

[112]

Nature of adsorption

Electrolytic

 media

 Ref.

116 Green Chemistry

ionic liquids ,

(II)

,

(IV)

Electrochemical,

angle

measurement

 SEM, EDX, contact

Langmuir adsorption

type

 isotherm, mixed

1M HCl

[113]

(III)

(ODA-TS)

 (OA-TS) (PPIB1) (PPIB4)

(MA1) (MA2)

Weight loss and

methods

electrochemical

Langmuir adsorption

type

 isotherm, mixed

1M HCl/1M H2SO4

[116]

Weight loss and

methods

Weight loss and DFT studies

Langmuir adsorption

 isotherm

1M HCl

[115]

electrochemical

Langmuir adsorption

type

 isotherm, mixed

1M HCl

[114]

(I)

isotherm. Polarization study suggested that investigated ionic liquid acted as mixed type inhibitor. Tseng and coworkers [118] investigated the corrosion characteristics of carbon steel, 304 stainless steel (304 SS) and pure titanium (Ti) in aluminum chloride–1-ethyl-3-methylimidazolium chloride ionic liquid for the first time. These authors reported the active-to-passive transition behavior for CS sample. Among the tested materials 304 SS exhibited the maximum stability in the high chloride environment. The most peculiar finding was that Ti was severally corroded in the ionic liquid because it does not undergo passivation. The ionic liquid in nonaqueous, low-oxygen and high halogen containing showed different corrosion behavior and mechanism. Similar observation has been reported by other authors for different metals including copper, nickel and stainless steel [119]. Recently, the inhibition behavior of 1,4-di [1 methylene-3-methyl imidazolium bromide]- benzene on mild steel corrosion in 1M H2SO4 have been studied using electrochemical and surface analysis methods [120]. The ionic liquid under taken in the study inhibits metallic corrosion by adsorbing on the surface which mechanism obeyed the Langmuir adsorption isotherm. The adsorption mechanism was supported by SEM, EDX and AFM analyses. Polarization study reveals that studied ionic liquid acted as mixed type inhibitor. The ongoing discussion reveals that although, several classes of ionic liquids have been used as effective inhibitors for mild steel corrosion in various aggressive media, however, imidazole based ionic liquids have been used most extensively [78–84, 89–96, 98–112, 114–116, 123].

the order: (PImC12 > PImC8 > PImC4). Adsorption of these ionic liquids followed the Langmuir adsorption isotherm. Four newly synthesized quaternary ammonium based surfactants in the series of hexanediyl-1,6-bis-(diethyl alkyl ammonium bromide), designated as CmC6Cm(Et)2Br (m = 10, 12, 14, 16), were synthesized and evaluated as inhibitors for aluminum corrosion in 1M HCl solution [127]. Results showed that all investigated surfactants act as good inhibitors and inhibit corrosion by becoming adsorbate at metal/electrolyte interfaces and their adsorption on metallic surface obeyed the Langmuir adsorption isotherm. Trombetta et al. [128] studied the stability of the aluminum in 1-butyl-3methylimidazolium tetrafluroborate ionic liquid and ethylene glycol mixtures using electrochemical impedance spectroscope (EIS). These authors observed decrease in polarization resistance and increase in the capacitance related with the passive oxide dielectric properties on increasing the ethylene glycol and/or water content in the mixtures. Presence of salts namely Na2B4O7.7H2O and NaH2PO4 in the mixtures, stabilize the oxide payer form over the metallic surface and thereby reduce the changes of metallic corrosion. The inhibition behavior of 1,3-bis(2-oxo-2 phenylethyl)-1H-imidazol-3-ium bromide (OPEIB) on 6061 Al-15 vol. pct. SiC(p) composite in 0.1M H2SO4 solution was studied by Shetty and Shetty [125] using electrochemical (EIS and PDP), SEM and EDX methods. The investigated ionic liquid exhibits the maximum efficiencies of 96.7 and 94% using PDP and EIS methods, respectively. Potentiodynamic polarization study further reveals that studied ionic liquid behaves as cathodic type inhibitor and its adsorption on the composite surface followed the Temkin adsorption. Li et al. [129] study the inhibition behavior of tetradecylpyridinium bromide (TDPB) on aluminum corrosion in 1M HCl solution using weight loss and electrochemical methods. Results of the investigation showed that TDPB inhibits the aluminum corrosion by adsorbing on the metallic surface. The adsorption of the TDPB followed the Langmuir adsorption isotherm. Polarization study suggested that TDPB acts as cathodic type inhibitor for acidic aluminum corrosion. Bermudez and coworkers [130] investigated the surface interactions of seven alkylimidazolium ionic liquids with aluminum alloy Al 2011 using immersion test. The immersion experiments for aluminum corrosion was carried out in 1 and 5 wt.% of 1-ethyl,3-methylimidazolium tetrafluoroborate (IL1) in water. Results showed that neat solution of ionic liquids did not cause any corrosion. The inhibition behavior was discussed on the basis of SEM, EDX, XPS

Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys

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119

and XRD techniques.

2.3. Ionic liquids as corrosion inhibitors for copper and zinc

Copper and its alloys have been extensively employed in industries for various applications such as building construction, electricity, electronics, coinages, ornamental and formation of industrial equipment due to their relatively good thermal, electrical, mechanical and corrosion resistance properties [131]. However, in presence of aggressive anions like chloride, sulphate and nitrate these materials undergo sever attack resulting into loss of these materials due to corrosion occurs [132, 133]. Similar to the aluminum the use of ionic liquids as corrosion inhibitors for copper and zinc is also limited as literature survey revealed that only few ionic liquids have been used as corrosion inhibitors for these materials. Qi-Bo and Yi-Xin [134] newly synthesized three ionic liquids namely 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4), 1-hexyl-3-methylimidazolium hydrogen sulfate ([HMIM]HSO4), and 1-octyl-3-methylimidazolium

#### 2.2. Ionic liquids as corrosion inhibitors for aluminum

Aluminum is the second most commonly used metal due to its several fascinating properties like its low atomic mass and negligible standard electrode potential. Several traditional organic and inorganic compounds have been used previously in order to protect dissolution of protective surface oxide film and ultimately decrease the corrosion rate. However, employment of the ionic liquids as corrosion inhibitors is limited as literature survey reveals that only few works are available describing the corrosion inhibition performance of ionic liquids. The inhibition performance of 1-butyl-3-methylimidazoliumchlorides (BMIC), 1-hexyl-3 methylimidazolium chlorides (HMIC) and 1-octyl-3-methylimidazoliumchlorides (OMIC) on aluminum corrosion in 1M HCl using electrochemical and weight loss methods showed that inhibition efficiencies of these ionic liquids increase with increasing their concentration and obeyed the order: OMIC > HMIC > BMIC [124]. Potentiodynamic study revealed that all ionic liquids acted as mixed type inhibitors and their adsorption on aluminum surface followed the Langmuir adsorption isotherm. The inhibition efficiency of an ecofriendly ionic liquid, 1,3-bis (2-oxo-2-phenylethyl)-1H-imidazol-3-ium bromide (OPEIB) on 6061 Al-15 alloy in 0.1 M H2SO4 solution using electrochemical impedance spectroscopy and potentiodynamic polarization, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopic methods revealed that it is a good corrosion inhibitor and its adsorption on aluminum surface obeyed the Temkin adsorption isotherm [125]. The three synthesized ILs, namely poly(ionic liquid)s (PILs), namely (poly(1-vinyl-3-dodecyl-imidazolium) (PImC12), poly(1-vinyl-3 octylimidazolium) (PImC8) and poly(1-vinyl-3-butylimidazolium) (PImC4) hexafluorophosphate) tested as inhibitor for aluminum alloy AA6061 in 0.1-1.0 M H2SO4 solution [126]. Results showed that they act as mixed type inhibitor and their inhibition efficiencies obeyed the order: (PImC12 > PImC8 > PImC4). Adsorption of these ionic liquids followed the Langmuir adsorption isotherm. Four newly synthesized quaternary ammonium based surfactants in the series of hexanediyl-1,6-bis-(diethyl alkyl ammonium bromide), designated as CmC6Cm(Et)2Br (m = 10, 12, 14, 16), were synthesized and evaluated as inhibitors for aluminum corrosion in 1M HCl solution [127]. Results showed that all investigated surfactants act as good inhibitors and inhibit corrosion by becoming adsorbate at metal/electrolyte interfaces and their adsorption on metallic surface obeyed the Langmuir adsorption isotherm. Trombetta et al. [128] studied the stability of the aluminum in 1-butyl-3methylimidazolium tetrafluroborate ionic liquid and ethylene glycol mixtures using electrochemical impedance spectroscope (EIS). These authors observed decrease in polarization resistance and increase in the capacitance related with the passive oxide dielectric properties on increasing the ethylene glycol and/or water content in the mixtures. Presence of salts namely Na2B4O7.7H2O and NaH2PO4 in the mixtures, stabilize the oxide payer form over the metallic surface and thereby reduce the changes of metallic corrosion. The inhibition behavior of 1,3-bis(2-oxo-2 phenylethyl)-1H-imidazol-3-ium bromide (OPEIB) on 6061 Al-15 vol. pct. SiC(p) composite in 0.1M H2SO4 solution was studied by Shetty and Shetty [125] using electrochemical (EIS and PDP), SEM and EDX methods. The investigated ionic liquid exhibits the maximum efficiencies of 96.7 and 94% using PDP and EIS methods, respectively. Potentiodynamic polarization study further reveals that studied ionic liquid behaves as cathodic type inhibitor and its adsorption on the composite surface followed the Temkin adsorption. Li et al. [129] study the inhibition behavior of tetradecylpyridinium bromide (TDPB) on aluminum corrosion in 1M HCl solution using weight loss and electrochemical methods. Results of the investigation showed that TDPB inhibits the aluminum corrosion by adsorbing on the metallic surface. The adsorption of the TDPB followed the Langmuir adsorption isotherm. Polarization study suggested that TDPB acts as cathodic type inhibitor for acidic aluminum corrosion. Bermudez and coworkers [130] investigated the surface interactions of seven alkylimidazolium ionic liquids with aluminum alloy Al 2011 using immersion test. The immersion experiments for aluminum corrosion was carried out in 1 and 5 wt.% of 1-ethyl,3-methylimidazolium tetrafluoroborate (IL1) in water. Results showed that neat solution of ionic liquids did not cause any corrosion. The inhibition behavior was discussed on the basis of SEM, EDX, XPS and XRD techniques.

#### 2.3. Ionic liquids as corrosion inhibitors for copper and zinc

isotherm. Polarization study suggested that investigated ionic liquid acted as mixed type inhibitor. Tseng and coworkers [118] investigated the corrosion characteristics of carbon steel, 304 stainless steel (304 SS) and pure titanium (Ti) in aluminum chloride–1-ethyl-3-methylimidazolium chloride ionic liquid for the first time. These authors reported the active-to-passive transition behavior for CS sample. Among the tested materials 304 SS exhibited the maximum stability in the high chloride environment. The most peculiar finding was that Ti was severally corroded in the ionic liquid because it does not undergo passivation. The ionic liquid in nonaqueous, low-oxygen and high halogen containing showed different corrosion behavior and mechanism. Similar observation has been reported by other authors for different metals including copper, nickel and stainless steel [119]. Recently, the inhibition behavior of 1,4-di [1 methylene-3-methyl imidazolium bromide]- benzene on mild steel corrosion in 1M H2SO4 have been studied using electrochemical and surface analysis methods [120]. The ionic liquid under taken in the study inhibits metallic corrosion by adsorbing on the surface which mechanism obeyed the Langmuir adsorption isotherm. The adsorption mechanism was supported by SEM, EDX and AFM analyses. Polarization study reveals that studied ionic liquid acted as mixed type inhibitor. The ongoing discussion reveals that although, several classes of ionic liquids have been used as effective inhibitors for mild steel corrosion in various aggressive media, however, imidazole based ionic liquids have been used most extensively [78–84,

Aluminum is the second most commonly used metal due to its several fascinating properties like its low atomic mass and negligible standard electrode potential. Several traditional organic and inorganic compounds have been used previously in order to protect dissolution of protective surface oxide film and ultimately decrease the corrosion rate. However, employment of the ionic liquids as corrosion inhibitors is limited as literature survey reveals that only few works are available describing the corrosion inhibition performance of ionic liquids. The inhibition performance of 1-butyl-3-methylimidazoliumchlorides (BMIC), 1-hexyl-3 methylimidazolium chlorides (HMIC) and 1-octyl-3-methylimidazoliumchlorides (OMIC) on aluminum corrosion in 1M HCl using electrochemical and weight loss methods showed that inhibition efficiencies of these ionic liquids increase with increasing their concentration and obeyed the order: OMIC > HMIC > BMIC [124]. Potentiodynamic study revealed that all ionic liquids acted as mixed type inhibitors and their adsorption on aluminum surface followed the Langmuir adsorption isotherm. The inhibition efficiency of an ecofriendly ionic liquid, 1,3-bis (2-oxo-2-phenylethyl)-1H-imidazol-3-ium bromide (OPEIB) on 6061 Al-15 alloy in 0.1 M H2SO4 solution using electrochemical impedance spectroscopy and potentiodynamic polarization, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopic methods revealed that it is a good corrosion inhibitor and its adsorption on aluminum surface obeyed the Temkin adsorption isotherm [125]. The three synthesized ILs, namely poly(ionic liquid)s (PILs), namely (poly(1-vinyl-3-dodecyl-imidazolium) (PImC12), poly(1-vinyl-3 octylimidazolium) (PImC8) and poly(1-vinyl-3-butylimidazolium) (PImC4) hexafluorophosphate) tested as inhibitor for aluminum alloy AA6061 in 0.1-1.0 M H2SO4 solution [126]. Results showed that they act as mixed type inhibitor and their inhibition efficiencies obeyed

89–96, 98–112, 114–116, 123].

118 Green Chemistry

2.2. Ionic liquids as corrosion inhibitors for aluminum

Copper and its alloys have been extensively employed in industries for various applications such as building construction, electricity, electronics, coinages, ornamental and formation of industrial equipment due to their relatively good thermal, electrical, mechanical and corrosion resistance properties [131]. However, in presence of aggressive anions like chloride, sulphate and nitrate these materials undergo sever attack resulting into loss of these materials due to corrosion occurs [132, 133]. Similar to the aluminum the use of ionic liquids as corrosion inhibitors for copper and zinc is also limited as literature survey revealed that only few ionic liquids have been used as corrosion inhibitors for these materials. Qi-Bo and Yi-Xin [134] newly synthesized three ionic liquids namely 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4), 1-hexyl-3-methylimidazolium hydrogen sulfate ([HMIM]HSO4), and 1-octyl-3-methylimidazolium hydrogen sulfate ([OMIM]HSO4) and studied their inhibition efficiency on copper corrosion in 0.5 M H2SO4 using electrochemical impedance spectroscopy and potentiodynamic polarization techniques. The inhibition efficiency of the ionic liquids follows the order: [OMIM] HSO4 > [HMIM]HSO4 > [BMIM]HSO4. Results obtained by these authors showed that adsorption of the studied ionic liquids followed the Langmuir adsorption isotherm. Polarization study revealed that these ionic liquids behaved as mixed type inhibitors. Gabler et al. [135] studied the inhibition performance of two ionic liquids namely (2-hydroxyethyl)-trimethyl-ammonium (IL1) and Butyl-trimethyl-ammonium (IL2) with identical anions; bis(trifluoromethyl-sulfonyl)imide on CuSn8P and steel 100Cr6, purchased from Metal Supermarkets (Brunn am Gebirge, Austria) using inductively coupled plasma optical emission spectrometry (ICP-OES), scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDX) and X-ray photoelectron spectroscopy (XPS) in water in the absence and presence of 1.5% of the ionic liquids. Manamela et al. [136] studied the inhibition performance of two ionic liquids; 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4 ] and 1-decyl-3-methylimidazolium tetrafluoroborate [DMIM] [BF4 ] on corrosion of zinc in 1M HCl using gravimetric analysis and theoretical Density Functional Theory (DFT) approach, using the B3LYP functional. Results showed that both the ionic liquids acted as good corrosion inhibitors and their inhibition efficiencies increase with increasing their concentrations. The inhibition efficiencies of the ionic liquids obeyed the order: [DMIM][BF4 ] > [BMIM][BF4 ]. Values of activation energy (Ea) and enthalpy of activation (ΔH) suggested that both the ionic liquids adsorbed over the surface through physisorption mechanism. Adsorption of these ionic liquids on metallic surface followed the Langmuir adsorption isotherm.

interactions between inhibitors and metallic surface. The DFT calculations provide several important parameters such as energies of highest occupied molecular orbital (EHOMO), lowest unoccupied molecular orbital (ELUMO), energy band gap (ELUMO EHOMO = ΔE), global electronegativity (χ), global hardness (η) and softness (σ), fraction of electron transfer (ΔN) and dipole moment (μ). In general, value of EHOMO is related with electron donating ability, while the value of ELUMO related with the electron accepting ability of the inhibitor molecules [74–77]. A higher value of EHOMO and lower value of ELUMO associated with high inhibition performance. The inhibition efficiency of inhibitor increases with decreasing the energy band gap (ΔE). A high value of global electronegativity (χ) is related with lower electron donating ability and therefore, the value of electronegativity (χ) inversely related with the inhibition efficiency order [74–77]. Inhibition efficiency of the inhibitor molecules decreases with increasing the hardness (η) and decreasing the softness (σ). Generally, inhibition performance of the inhibitor molecules increases with increasing their dipole moment (μ), however, negative trends of the inhibition efficiency is also reported by several authors [74–77]. Lastly, the value of electron transfer gives direct information about the relative extent of metalinhibitor interactions. A high value of ΔN is associated with high charge transfer and therefore

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The DFT based quantum chemical calculations have also been employed to describe the adsorption behavior of some ionic liquids on the metallic surface. Our research group [102] studied the adsorption behavior of four imidazolium-based ionic liquids, namely 1-propyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([PMIM][NTf2), 1-butyl-3-methylimidazoliumbis(trifluoromethyl-sulfonyl) imide ([BMIM][NTf2), 1-hexyl-3-methylimidazolium bis (trifluoromethyl-sulfonyl) imide([HMIM][NTf2]), and 1-propyl-2,3-methylimidazolium bis (trifluoromethyl-sulfonyl) imide ([PDMIM][NTf2]) on mild steel corrosion in 1M HCl using experimental and quantum chemical calculations. The inhibition efficiencies of these ionic liquids follow the experimental trend: [PDMIM][NTf2] > [HMIM][NTf2] > [BMIM][NTf2] > [PMIM][NTf2]. The values of EHOMO and ELUMO are well satisfied the experimental order of inhibition efficiency. Results showed that [PDMIM][NTf2] exhibited the lowest value of ΔE and therefore related with the highest chemical reactivity and inhibition efficiency. The values of dipole moment (μ) and the molecular volume (MV) did not show any regular trends. However, the values of global softness (σ) again show that the [PDMIM][NTf2] is most soft molecule among the tested compounds thereby associated with highest chemical reactivity and inhibition efficiency. The quantum chemical calculations provide good insight about the inhibition mechanism and well supported the experimental order of inhibition efficiency. Similar observations were reported for few other metals and alloys in several corrosive media [82, 139–143].

Similar to most of the organic corrosion inhibitors, ionic liquids (ILs) inhibit metallic corrosion by blocking the anodic and cathodic sites present over the metallic surface [78, 144, 145]. Therefore, inhibition of metallic corrosion in presence of ionic liquids involves blocking of anodic oxidative metallic dissolution as well as cathodic hydrogen evolution reactions [78, 144]. The mechanism of metallic (M) corrosion inhibition by ionic liquids in

high inhibition efficiency [74–77, 102].

4. Mechanism of corrosion inhibition

#### 2.4. Ionic liquids as corrosion inhibitors for magnesium

Unlike active light metals such as aluminum and titanium, magnesium based alloys do not form protective passivating film. Moreover, these alloys easily react with the components of environment to from hydroxides, oxides, carbonates films that are highly porous, inhomogeneous and poorly bonded that cannot provide satisfactory protection to the metals against corrosion. Among the available methods of corrosion protection, organic coating is one of the best methods. Huanga et al. [137] has presented an early review on the corrosion protection of magnesium by some ionic liquids. However, present chapter is describing the few recent advances in the utilization of ionic liquids as corrosion inhibitors. Suna et al. [138] have investigated the inhibition effect of six phosphonium cation based ionic liquids (ILs) namely, tetradecyltrihexylphosphonium diphenylphosphate (1), tetradecyltrihexylphosphoniumdibutylphosphate (2), tetradecyltrihexylphosphonium bis(2-ethylhexyl) phosphate (3), tetradecyltrihexyl phosphonium diisobutyldithiophosphinate (4), tetradecyltrihexylphosphoniumbis(2,4,4-trimethyl pentyl) phosphonate (5), and tetradecyltrihexyl phosphonium O,O-diethyl dithiophosphate on magnesium alloys using electrochemical and surface investigation methods.

#### 3. Ionic liquids as corrosion inhibitors: DFT study

Nowadays, several computational methods particularly, DFT (Density Functional Theory) based quantum chemical calculations have been emerged as potential tools for studying the interactions between inhibitors and metallic surface. The DFT calculations provide several important parameters such as energies of highest occupied molecular orbital (EHOMO), lowest unoccupied molecular orbital (ELUMO), energy band gap (ELUMO EHOMO = ΔE), global electronegativity (χ), global hardness (η) and softness (σ), fraction of electron transfer (ΔN) and dipole moment (μ). In general, value of EHOMO is related with electron donating ability, while the value of ELUMO related with the electron accepting ability of the inhibitor molecules [74–77]. A higher value of EHOMO and lower value of ELUMO associated with high inhibition performance. The inhibition efficiency of inhibitor increases with decreasing the energy band gap (ΔE). A high value of global electronegativity (χ) is related with lower electron donating ability and therefore, the value of electronegativity (χ) inversely related with the inhibition efficiency order [74–77]. Inhibition efficiency of the inhibitor molecules decreases with increasing the hardness (η) and decreasing the softness (σ). Generally, inhibition performance of the inhibitor molecules increases with increasing their dipole moment (μ), however, negative trends of the inhibition efficiency is also reported by several authors [74–77]. Lastly, the value of electron transfer gives direct information about the relative extent of metalinhibitor interactions. A high value of ΔN is associated with high charge transfer and therefore high inhibition efficiency [74–77, 102].

The DFT based quantum chemical calculations have also been employed to describe the adsorption behavior of some ionic liquids on the metallic surface. Our research group [102] studied the adsorption behavior of four imidazolium-based ionic liquids, namely 1-propyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([PMIM][NTf2), 1-butyl-3-methylimidazoliumbis(trifluoromethyl-sulfonyl) imide ([BMIM][NTf2), 1-hexyl-3-methylimidazolium bis (trifluoromethyl-sulfonyl) imide([HMIM][NTf2]), and 1-propyl-2,3-methylimidazolium bis (trifluoromethyl-sulfonyl) imide ([PDMIM][NTf2]) on mild steel corrosion in 1M HCl using experimental and quantum chemical calculations. The inhibition efficiencies of these ionic liquids follow the experimental trend: [PDMIM][NTf2] > [HMIM][NTf2] > [BMIM][NTf2] > [PMIM][NTf2]. The values of EHOMO and ELUMO are well satisfied the experimental order of inhibition efficiency. Results showed that [PDMIM][NTf2] exhibited the lowest value of ΔE and therefore related with the highest chemical reactivity and inhibition efficiency. The values of dipole moment (μ) and the molecular volume (MV) did not show any regular trends. However, the values of global softness (σ) again show that the [PDMIM][NTf2] is most soft molecule among the tested compounds thereby associated with highest chemical reactivity and inhibition efficiency. The quantum chemical calculations provide good insight about the inhibition mechanism and well supported the experimental order of inhibition efficiency. Similar observations were reported for few other metals and alloys in several corrosive media [82, 139–143].

#### 4. Mechanism of corrosion inhibition

hydrogen sulfate ([OMIM]HSO4) and studied their inhibition efficiency on copper corrosion in 0.5 M H2SO4 using electrochemical impedance spectroscopy and potentiodynamic polarization techniques. The inhibition efficiency of the ionic liquids follows the order: [OMIM] HSO4 > [HMIM]HSO4 > [BMIM]HSO4. Results obtained by these authors showed that adsorption of the studied ionic liquids followed the Langmuir adsorption isotherm. Polarization study revealed that these ionic liquids behaved as mixed type inhibitors. Gabler et al. [135] studied the inhibition performance of two ionic liquids namely (2-hydroxyethyl)-trimethyl-ammonium (IL1) and Butyl-trimethyl-ammonium (IL2) with identical anions; bis(trifluoromethyl-sulfonyl)imide on CuSn8P and steel 100Cr6, purchased from Metal Supermarkets (Brunn am Gebirge, Austria) using inductively coupled plasma optical emission spectrometry (ICP-OES), scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDX) and X-ray photoelectron spectroscopy (XPS) in water in the absence and presence of 1.5% of the ionic liquids. Manamela et al. [136] studied the inhibition performance of two ionic liquids; 1-butyl-3-methylimidazolium

] on corrosion of zinc in 1M HCl using gravimetric analysis and theoretical Density Functional Theory (DFT) approach, using the B3LYP functional. Results showed that both the ionic liquids acted as good corrosion inhibitors and their inhibition efficiencies increase with increasing their concentrations. The inhibition efficiencies of the ionic liquids obeyed the order:

suggested that both the ionic liquids adsorbed over the surface through physisorption mechanism. Adsorption of these ionic liquids on metallic surface followed the Langmuir adsorption

Unlike active light metals such as aluminum and titanium, magnesium based alloys do not form protective passivating film. Moreover, these alloys easily react with the components of environment to from hydroxides, oxides, carbonates films that are highly porous, inhomogeneous and poorly bonded that cannot provide satisfactory protection to the metals against corrosion. Among the available methods of corrosion protection, organic coating is one of the best methods. Huanga et al. [137] has presented an early review on the corrosion protection of magnesium by some ionic liquids. However, present chapter is describing the few recent advances in the utilization of ionic liquids as corrosion inhibitors. Suna et al. [138] have investigated the inhibition effect of six phosphonium cation based ionic liquids (ILs) namely, tetradecyltrihexylphosphonium diphenylphosphate (1), tetradecyltrihexylphosphoniumdibutylphosphate (2), tetradecyltrihexylphosphonium bis(2-ethylhexyl) phosphate (3), tetradecyltrihexyl phosphonium diisobutyldithiophosphinate (4), tetradecyltrihexylphosphoniumbis(2,4,4-trimethyl pentyl) phosphonate (5), and tetradecyltrihexyl phosphonium O,O-diethyl dithiophosphate on magne-

Nowadays, several computational methods particularly, DFT (Density Functional Theory) based quantum chemical calculations have been emerged as potential tools for studying the

] and 1-decyl-3-methylimidazolium tetrafluoroborate [DMIM]

]. Values of activation energy (Ea) and enthalpy of activation (ΔH)

tetrafluoroborate [BMIM][BF4

] > [BMIM][BF4

2.4. Ionic liquids as corrosion inhibitors for magnesium

sium alloys using electrochemical and surface investigation methods.

3. Ionic liquids as corrosion inhibitors: DFT study

[BF4

120 Green Chemistry

[DMIM][BF4

isotherm.

Similar to most of the organic corrosion inhibitors, ionic liquids (ILs) inhibit metallic corrosion by blocking the anodic and cathodic sites present over the metallic surface [78, 144, 145]. Therefore, inhibition of metallic corrosion in presence of ionic liquids involves blocking of anodic oxidative metallic dissolution as well as cathodic hydrogen evolution reactions [78, 144]. The mechanism of metallic (M) corrosion inhibition by ionic liquids in

sulphuric acid has been described below. The inhibition mechanism of metallic corrosion by ionic liquids in other protic acidic solutions such as in HCl and HNO3 will be similar because of their similar nature. The only difference in their nature is that they possess different counter ions (Cl�, NO3 �) rather than sulphate ion of sulphuric acid. According to Likhanova et al. [78], anodic dissolution of metals (M) in aqueous acidic solution (e.g. H2SO4) can be represented as follows [78]:

$$M + nH\_2O \longleftrightarrow M(H\_2O)n\_{ads} \tag{1}$$

The cathodic hydrogen evolution reaction (HER) can be represented by following simple

Generally, the hydrogen evolution reaction (HER) follows two very common mechanisms that is, Volmer-Heyrovsky mechanism represented by Eqs. (12) and (13) or according to the Tafel hydrogen evolution mechanism represented by Eq. (14). In acidic medium, the Volmer-Heyrovsky and

During the first step of cathodic reactions hydrogen ions (or hydronium ions) first adsorbed on the metallic surface by Volmer mechanism followed by discharge of hydrogen gas by Heyrovsky and Tafel mechanism represented by Eqs. (13-14). All these reactions do not occur with the same rate. Generally, a slow reaction step is followed by a fast reaction step [151]. If the Volmer reaction is fast, then Heyrovsky and/or Tafel reactions occur with slower rate and vice versa. Presence of the organic corrosion inhibitors (ILs) in the corrosive solution may retards or slow down the formation of MHads or retards the electron transfer to the hydronium ions and suppresses the Heyrovsky reactions (13). In general, in corrosive medium, the adsorbed hydrogen on metallic surface recombined and evolved as the bubbles of hydrogen gas. The formation of bubble and its evolution is the second step in the HER. The formation of hydrogen gas either occurs through hydrogen atom-atom combination as denoted by Volmer-Tafel Eq. (14) or may results through hydrogen atom-hydrogen ion combination as represented by Volmer-Heyrovsky Eq. (13) [151].

� ! H<sup>2</sup>ð Þ<sup>g</sup> þ 2OH� (11)

http://dx.doi.org/10.5772/intechopen.70421

123

Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys

� ! MHads þ H2O ð Þ Volmer, V (12)

� ! <sup>H</sup><sup>2</sup> <sup>þ</sup> <sup>M</sup> <sup>þ</sup> <sup>H</sup>2<sup>O</sup> Heyrovsky, <sup>H</sup> (13)

� ! M ILsC ð Þads (15)

) starts competing with

MHads þ MHads ! H<sup>2</sup> þ 2M ð Þ Tafel, T (14)

H2O þ 2e

Volmer-Tafel hydrogen evolution mechanisms have been shown below [148–150]:

In the presence of inhibitors (ILs), cathodic can be represented as follows:

simultaneously. At cathode, the cationic part of ionic liquids (ILsC<sup>+</sup>

strengthen each other through synergism [153–160].

M þ ILsC<sup>þ</sup> þ e

Initially, adsorption of hydronium ions and evolution of hydrogen gas occur at cathodic sites,

hydrogen ions for electrons [78, 152]. In general, ILsC+ has large molecular size and therefore replaces greater number of water molecules from the metallic surface. After their adsorption, cationic part of the ILs accepts electrons from the metal (M) which results into the formation of electrically neutral ionic liquids (inhibitors). The neutral species transfer (donation) their nonbonding (of heteroatoms) and π-electrons into the d-orbitals of the surface metallic atoms resulting into the formation of co-ordinate bonds between metal and ILs (chemisorption) as reported for several organic conventional inhibitors [78, 146, 153–156]. However, metals are already electron rich species; this type of donation causes inter electronic repulsion which interns resulted into transfer of electrons from d-orbitals of the surface metallic atoms to antibonding molecular orbitals of the ILs (retro-donation). Both donation and retro-donation

M þ H3O<sup>þ</sup> þ e

MHads þ H3O<sup>þ</sup> þ e

stoichimmetry equation [148]:

$$M(H\_2O)n\_{\text{ads}} + SO\_4^{2-} \longleftrightarrow M\left[(H\_2O)\_nSO\_4^{2-}\right]\_{\text{ads}}\tag{2}$$

$$M\left[\left(H\_2O\right)\_nSO\_4^{2-}\right]\_{ads} \longrightarrow M\left[\left(H\_2O\right)\_nSO\_4\right]\_{ads} + 2e^- \tag{3}$$

$$\mathrm{M} \left[ (\mathrm{H}\_{2}\mathrm{O})\_{n}\mathrm{SO}\_{4} \right]\_{\mathrm{ads}} \longrightarrow \mathrm{M}^{2+} + \mathrm{OH}^{-} + \mathrm{SO}\_{4}^{2-} + \mathrm{H}^{+} \tag{4}$$

However, in presence of ionic liquids, anodic reactions can be represented as follows:

$$M + nH\_2O \longleftrightarrow M(H\_2O)n\_{ads} \tag{5}$$

$$M(H\_2O)n\_{\rm ads} + SO\_4^{2-} \longleftrightarrow M\left[(H\_2O)\_nSO\_4^{2-}\right]\_{\rm ads} \tag{6}$$

$$\mathrm{M(H\_2O)\_nSO\_4^{2-}}|\_{ads} + ILs\mathrm{C}^+ \longrightarrow \mathrm{M(H\_2O)\_nSO\_4ILs\mathrm{C}}|\_{ads} \tag{7}$$

$$\mathrm{M(H\_2O)\_nSO\_4ILs\mathrm{Cl}\_{ads}^- + ILs\mathrm{C}^+ + SO\_4^{2-} \longrightarrow \mathrm{[M(H\_2O)\_nSO\_4ILs\mathrm{C}\right]^-} \\ \mathrm{lLs\mathrm{C}^+SO\_4^{2-} / ILs\mathrm{C}^+ \qquad \text{(8)}$$

$$M + X^- \longleftrightarrow (MX^-)\_{\text{ads}} \tag{9}$$

$$\left(\mathrm{M}X^{-}\right)\_{\mathrm{ads}} + \mathrm{I}\mathrm{L}s\mathrm{C}^{+} \longleftrightarrow \left(\mathrm{MX}^{-}\mathrm{I}\mathrm{L}s\mathrm{C}^{+}\right)\_{\mathrm{ads}}\tag{10}$$

where, ILsC<sup>+</sup> and X� represent the cationic counter part of the ionic liquids (mostly organic) and anionic counter part of the ionic liquid, respectively. It is important to mention that the concentration of sulphate ions is much higher as comared to the concentration of anionic counter part of the ionic liquids (X�) that results into formation of [M(H2O) SO<sup>2</sup>� 4]ads in larger proporsion than [MX�]ads. Nevertheless, these both anionic charged species attracted positively charged cationic counter part of the ionic liquids (ILsC<sup>+</sup> ) by electrostatic force of attraction (physisoprtion) and forms monomolecular layer as an insoluble complex on the metallic surface [78, 145]. The adsortion of the ILsC<sup>+</sup> on metallic surface causes change in the surface polarity which induces the adsorption of the sulphate and X� ions again which results into multimolecular layer [78, 146]. The multimolecular layers are stabilized by Vanderwaal's cohesion force acting beteween organic moeity of the ionic liquids which causes a more closely adsorbed film at metal/electrolyte interfaces. Generally, the cationic part (ILsC<sup>+</sup> ) interacts with the metallic surface and forms the multimolecular layers while rest of the part of the ionic liquids form hydrophobic hemi-micelles, ad-micelles and/or surface aggregation [78, 147]. The adsorbed multimolecular layers of the ILs isolate the metal (M) from corrosive enviroment and protect from corrosive dissolution.

The cathodic hydrogen evolution reaction (HER) can be represented by following simple stoichimmetry equation [148]:

sulphuric acid has been described below. The inhibition mechanism of metallic corrosion by ionic liquids in other protic acidic solutions such as in HCl and HNO3 will be similar because of their similar nature. The only difference in their nature is that they possess different

et al. [78], anodic dissolution of metals (M) in aqueous acidic solution (e.g. H2SO4) can be

M Hð Þ <sup>2</sup>O nads þ SO<sup>4</sup>

M Hð Þ <sup>2</sup>O nads þ SO<sup>4</sup>

ads <sup>þ</sup> ILsC<sup>þ</sup> <sup>þ</sup> SO<sup>2</sup>�

tively charged cationic counter part of the ionic liquids (ILsC<sup>+</sup>

M Hð Þ <sup>2</sup><sup>O</sup> <sup>n</sup>SO<sup>2</sup>�

�

4 

However, in presence of ionic liquids, anodic reactions can be represented as follows:

M Hð Þ <sup>2</sup><sup>O</sup> <sup>n</sup>SO<sup>2</sup>�

M Hð Þ <sup>2</sup>O <sup>n</sup>SO<sup>4</sup> 

�) rather than sulphate ion of sulphuric acid. According to Likhanova

<sup>2</sup>� ! M Hð Þ <sup>2</sup><sup>O</sup> <sup>n</sup>SO<sup>2</sup>�

<sup>2</sup>� ! M Hð Þ <sup>2</sup><sup>O</sup> <sup>n</sup>SO<sup>2</sup>�

<sup>4</sup> ! M Hð Þ <sup>2</sup><sup>O</sup> <sup>n</sup>SO4ILsC �

<sup>4</sup> �ads <sup>þ</sup> ILsC<sup>þ</sup>!M Hð Þ <sup>2</sup><sup>O</sup> <sup>n</sup>SO4ILsC�

MX� ð Þads <sup>þ</sup> ILsCþ ! MX�ILsC<sup>þ</sup>

where, ILsC<sup>+</sup> and X� represent the cationic counter part of the ionic liquids (mostly organic) and anionic counter part of the ionic liquid, respectively. It is important to mention that the concentration of sulphate ions is much higher as comared to the concentration of anionic

proporsion than [MX�]ads. Nevertheless, these both anionic charged species attracted posi-

tion (physisoprtion) and forms monomolecular layer as an insoluble complex on the metallic surface [78, 145]. The adsortion of the ILsC<sup>+</sup> on metallic surface causes change in the surface polarity which induces the adsorption of the sulphate and X� ions again which results into multimolecular layer [78, 146]. The multimolecular layers are stabilized by Vanderwaal's cohesion force acting beteween organic moeity of the ionic liquids which causes a more closely

the metallic surface and forms the multimolecular layers while rest of the part of the ionic liquids form hydrophobic hemi-micelles, ad-micelles and/or surface aggregation [78, 147]. The adsorbed multimolecular layers of the ILs isolate the metal (M) from corrosive enviroment and

counter part of the ionic liquids (X�) that results into formation of [M(H2O) SO<sup>2</sup>�

adsorbed film at metal/electrolyte interfaces. Generally, the cationic part (ILsC<sup>+</sup>

ads!M Hð Þ <sup>2</sup><sup>O</sup> <sup>n</sup>SO<sup>4</sup> 

ads!M<sup>2</sup><sup>þ</sup> <sup>þ</sup> OH� <sup>þ</sup> SO<sup>2</sup>�

M þ nH2O ! M Hð Þ <sup>2</sup>O nads (1)

4 

ads þ 2e

M þ nH2O ! M Hð Þ <sup>2</sup>O nads (5)

4 

M þ X� ! MX� ð Þads (9)

�

adsILsCþSO<sup>2</sup>�

ads (2)

� (3)

ads (6)

ads (7)

ads (10)

) by electrostatic force of attrac-

<sup>4</sup> =ILsC<sup>þ</sup> (8)

4]ads in larger

) interacts with

<sup>4</sup> þ H<sup>þ</sup> (4)

counter ions (Cl�, NO3

122 Green Chemistry

represented as follows [78]:

M Hð Þ <sup>2</sup>O <sup>n</sup>SO4ILsC�

protect from corrosive dissolution.

$$\rm H\_2O + 2e^- \longleftrightarrow H\_{2(g)} + 2OH^- \tag{11}$$

Generally, the hydrogen evolution reaction (HER) follows two very common mechanisms that is, Volmer-Heyrovsky mechanism represented by Eqs. (12) and (13) or according to the Tafel hydrogen evolution mechanism represented by Eq. (14). In acidic medium, the Volmer-Heyrovsky and Volmer-Tafel hydrogen evolution mechanisms have been shown below [148–150]:

$$2\text{ }M + H\_3O^+ + e^- \longleftrightarrow MH\_{ads} + H\_2O \quad \text{(Volmer, V)}\tag{12}$$

$$4\text{ }MH\_{\text{ads}} + H\_3O^+ + e^- \longleftrightarrow H\_2 + M + H\_2O \quad \text{(Heyrovsky, H)}\tag{13}$$

$$\text{M} \text{M} \text{H}\_{\text{ads}} + \text{M} \text{H}\_{\text{ads}} \longleftrightarrow \text{H}\_2 + 2\text{M} \quad \text{(Tafel, T)} \tag{14}$$

During the first step of cathodic reactions hydrogen ions (or hydronium ions) first adsorbed on the metallic surface by Volmer mechanism followed by discharge of hydrogen gas by Heyrovsky and Tafel mechanism represented by Eqs. (13-14). All these reactions do not occur with the same rate. Generally, a slow reaction step is followed by a fast reaction step [151]. If the Volmer reaction is fast, then Heyrovsky and/or Tafel reactions occur with slower rate and vice versa. Presence of the organic corrosion inhibitors (ILs) in the corrosive solution may retards or slow down the formation of MHads or retards the electron transfer to the hydronium ions and suppresses the Heyrovsky reactions (13). In general, in corrosive medium, the adsorbed hydrogen on metallic surface recombined and evolved as the bubbles of hydrogen gas. The formation of bubble and its evolution is the second step in the HER. The formation of hydrogen gas either occurs through hydrogen atom-atom combination as denoted by Volmer-Tafel Eq. (14) or may results through hydrogen atom-hydrogen ion combination as represented by Volmer-Heyrovsky Eq. (13) [151].

In the presence of inhibitors (ILs), cathodic can be represented as follows:

$$M + ILs\mathbb{C}^+ + e^- \longleftrightarrow M(ILs\mathbb{C})\_{ads} \tag{15}$$

Initially, adsorption of hydronium ions and evolution of hydrogen gas occur at cathodic sites, simultaneously. At cathode, the cationic part of ionic liquids (ILsC<sup>+</sup> ) starts competing with hydrogen ions for electrons [78, 152]. In general, ILsC+ has large molecular size and therefore replaces greater number of water molecules from the metallic surface. After their adsorption, cationic part of the ILs accepts electrons from the metal (M) which results into the formation of electrically neutral ionic liquids (inhibitors). The neutral species transfer (donation) their nonbonding (of heteroatoms) and π-electrons into the d-orbitals of the surface metallic atoms resulting into the formation of co-ordinate bonds between metal and ILs (chemisorption) as reported for several organic conventional inhibitors [78, 146, 153–156]. However, metals are already electron rich species; this type of donation causes inter electronic repulsion which interns resulted into transfer of electrons from d-orbitals of the surface metallic atoms to antibonding molecular orbitals of the ILs (retro-donation). Both donation and retro-donation strengthen each other through synergism [153–160].

### 5. Conclusions and future perspectives

On the basis of ongoing discussion it can be concluded that ionic liquids are green and sustainable inhibitors for corrosion of metals and alloys. The superiority of the use of ionic liquids as corrosion inhibitors compared to traditional volatile (toxic) corrosion inhibitors is based on the fact that they possess several fascinating properties such lower volatility, noninflammability, non-toxic nature, chemical stability, high solubility in the polar solvents and their ability to easily adsorb on the metallic surface. Adsorption of the ionic liquids over the metallic surface results into formation of protective film which isolates the metals (alloys) from the corrosive environment and thereby inhibits corrosion. Among several available ionic liquids, imidazole based ionic liquids have been most extensively used. Some reports described the adsorption behavior of ionic liquids on metallic surface using DFT based quantum chemical calculations. However, the use of this technique should be further explored owing to its green nature to understand the mechanistic aspects of corrosion inhibition. The use of ionic liquids as corrosion inhibitors is preferred comparing with traditional inhibitors due to several physiochemical properties advantageous including their high solubility, non-toxic, high conductivity, and non-flammability, less volatility as well as high chemical stability and more importantly due to their "green and sustainable" nature.

[3] Winkleman A, Svedberg EB, Schafrik E, Duquette DJ. Advanced Materials & Processes.

Ionic Liquids as Green Corrosion Inhibitors for Industrial Metals and Alloys

http://dx.doi.org/10.5772/intechopen.70421

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## Author details

Chandrabhan Verma1,2, Eno E. Ebenso2 and Mumtaz Ahmad Quraishi1,3\*

\*Address all correspondence to: maquraishi.apc@itbhu.ac.in

1 Department of Chemistry, Indian Institute of Technology, Banaras Hindu University, Varanasi, India

2 Material Science Innovation and Modelling (MaSIM) Research Focus Area, Department of Chemistry, Faculty of Agriculture, Science and Technology, North-West University (Mafikeng Campus), Private Bag, Mmabatho, South Africa

3 Center of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia

#### References


5. Conclusions and future perspectives

importantly due to their "green and sustainable" nature.

\*Address all correspondence to: maquraishi.apc@itbhu.ac.in

Inc., Hoboken New Jersey, Canada; 2007. pp. 1-3

Campus), Private Bag, Mmabatho, South Africa

Petroleum and Minerals, Dhahran, Saudi Arabia

Chandrabhan Verma1,2, Eno E. Ebenso2 and Mumtaz Ahmad Quraishi1,3\*

1 Department of Chemistry, Indian Institute of Technology, Banaras Hindu University,

2 Material Science Innovation and Modelling (MaSIM) Research Focus Area, Department of Chemistry, Faculty of Agriculture, Science and Technology, North-West University (Mafikeng

3 Center of Research Excellence in Corrosion, Research Institute, King Fahd University of

[1] Revie RW, Uhling HH. Corrosion and Corrosion Control. 4th ed. John Wiley & Sons,

[2] Masadeh S. The Effect of Added Carbon Black to Concrete Mix on Corrosion of Steel in Concrete, Journal of Minerals and Materials Characterization and Engineering. 2015;3:

Author details

124 Green Chemistry

Varanasi, India

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On the basis of ongoing discussion it can be concluded that ionic liquids are green and sustainable inhibitors for corrosion of metals and alloys. The superiority of the use of ionic liquids as corrosion inhibitors compared to traditional volatile (toxic) corrosion inhibitors is based on the fact that they possess several fascinating properties such lower volatility, noninflammability, non-toxic nature, chemical stability, high solubility in the polar solvents and their ability to easily adsorb on the metallic surface. Adsorption of the ionic liquids over the metallic surface results into formation of protective film which isolates the metals (alloys) from the corrosive environment and thereby inhibits corrosion. Among several available ionic liquids, imidazole based ionic liquids have been most extensively used. Some reports described the adsorption behavior of ionic liquids on metallic surface using DFT based quantum chemical calculations. However, the use of this technique should be further explored owing to its green nature to understand the mechanistic aspects of corrosion inhibition. The use of ionic liquids as corrosion inhibitors is preferred comparing with traditional inhibitors due to several physiochemical properties advantageous including their high solubility, non-toxic, high conductivity, and non-flammability, less volatility as well as high chemical stability and more


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**Chapter 7**

**Provisional chapter**

**Nanoscale Zero Valent Iron for Environmental**

**Nanoscale Zero Valent Iron for Environmental** 

DOI: 10.5772/intechopen.72737

In the course of developing methods to treat heavy metal contaminants in wastewater, nanoscale zerovalent iron (nZVI) has been found to be an alternative approach. This nanoparticle has been used to remove metals such as Cr6+, Cu2+, Pb2+, Ba2+, As3+, As5+, and Co2+ from aqueous solutions. Iron nanoparticles are useful for decontamination purposes due to their smaller size, surface area-to-weight ratio, and capacity to remove groundwater contaminants. The large specific surface area of the iron nanoparticles further fosters enhanced reactivity for the transformation of environmental pollutants. Because of their smaller size, nanoscale-based iron materials are much more reactive than conventional iron powders, and they can be suspended in slurry and pumped straight to the contaminated site. The ZVI is often applied for the remediation of wastewater or groundwater with several kinds of reducible contaminants, which are near its surface reduction potential. This chapter seeks to present the efficiency of zerovalent iron nanoparticles (nZVI) to remedy the cadmium ion pollution in water as well as the use of the remediation product

**Keywords:** nanoscale zero valent iron, heavy metals, environmental remediation,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

Environmental pollution is one of the most important problems in the world and is the focus of a wide array of studies in the scientific community [1]. The development of advanced technology and rapid industrialization are the most predominant factors that increase environmental pollution [2]. One of the major hazards to human health from environmental contamination is heavy metals due to their tendency to bioaccumulate in plants and animals that are part of the human food chain [3]. Numerous anthropogenic activities such as mining,

**Cadmium Metal Treatment**

**Cadmium Metal Treatment**

http://dx.doi.org/10.5772/intechopen.72737

in photoelectrochemical devices.

photoelectrochemical solar cells

**Abstract**

**1. Introduction**

Keyla T. Soto-Hidalgo and Carlos R. Cabrera

Additional information is available at the end of the chapter

Keyla T. Soto-Hidalgo and Carlos R. Cabrera

Additional information is available at the end of the chapter

**Provisional chapter**

### **Nanoscale Zero Valent Iron for Environmental Cadmium Metal Treatment Cadmium Metal Treatment**

**Nanoscale Zero Valent Iron for Environmental** 

DOI: 10.5772/intechopen.72737

Keyla T. Soto-Hidalgo and Carlos R. Cabrera Additional information is available at the end of the chapter

Keyla T. Soto-Hidalgo and Carlos R. Cabrera

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72737

#### **Abstract**

In the course of developing methods to treat heavy metal contaminants in wastewater, nanoscale zerovalent iron (nZVI) has been found to be an alternative approach. This nanoparticle has been used to remove metals such as Cr6+, Cu2+, Pb2+, Ba2+, As3+, As5+, and Co2+ from aqueous solutions. Iron nanoparticles are useful for decontamination purposes due to their smaller size, surface area-to-weight ratio, and capacity to remove groundwater contaminants. The large specific surface area of the iron nanoparticles further fosters enhanced reactivity for the transformation of environmental pollutants. Because of their smaller size, nanoscale-based iron materials are much more reactive than conventional iron powders, and they can be suspended in slurry and pumped straight to the contaminated site. The ZVI is often applied for the remediation of wastewater or groundwater with several kinds of reducible contaminants, which are near its surface reduction potential. This chapter seeks to present the efficiency of zerovalent iron nanoparticles (nZVI) to remedy the cadmium ion pollution in water as well as the use of the remediation product in photoelectrochemical devices.

**Keywords:** nanoscale zero valent iron, heavy metals, environmental remediation, photoelectrochemical solar cells

#### **1. Introduction**

Environmental pollution is one of the most important problems in the world and is the focus of a wide array of studies in the scientific community [1]. The development of advanced technology and rapid industrialization are the most predominant factors that increase environmental pollution [2]. One of the major hazards to human health from environmental contamination is heavy metals due to their tendency to bioaccumulate in plants and animals that are part of the human food chain [3]. Numerous anthropogenic activities such as mining,

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

landfills, electroplating, metal processing, textile, petroleum refining, pesticides, battery and paint manufacturing, and printing and photographic industries release these metals into the environment. Heavy metals can persist for a long time in the environment [4].

ion exchange columns, electrochemical removal, filtration, and membrane technologies [8], but these methods are expensive and use many equipments to efficiently remove the contaminants. On the other hand, following the principles of Green Chemistry is necessary to use alternative products that prevent waste after remediation process, use less hazardous chemical synthesis, and minimize energy requirements of all chemical processes and environmental and economic

Nanoscale Zero Valent Iron for Environmental Cadmium Metal Treatment

http://dx.doi.org/10.5772/intechopen.72737

137

Iron nanoparticles are a new generation of materials for environmental remediation. Various metallic ions, including Pb2+, Cr6+, Ni2+, As3+, As5+, Cd2+, Cu2+, Zn2+, and Ba2+ have been fixated from water using this new technology [14]. In situ remediation strategies are useful to reduce the mobile fraction of metals and metalloids in the soil that could reach the groundwater or be taken up by soil organisms. As such, several strategies have been used to promote the immobilization of metals in soil [15]. In the course of developing suitable options to remove heavy metal contaminants from wastewater, nanoscale zero valent iron (nZVI) particles have been found to be an alternative approach to reduce the concentration of several kinds of contaminants, mainly targeting chlorinated organic contaminants, inorganic anions, metals, and metalloids [15–19]. Although the benefits of this strategy are evident, governments and environmental agencies must evaluate any associated environmental risks because currently

Previous column experiments have showed the effectiveness of nZVI for the in situ immobilization of heavy metals, which reduces their potential leachability, as a strategy to prevent their transport into deeper soil layers, rivers, and groundwater [21]. Iron nanoparticles are particularly attractive for environmental remediation because these are much more reactive than iron powders and they can be suspended in slurry and moved to the polluted site [22, 23]. Recently, the synthesis and utilization of iron-based nanomaterials with novel properties and functions have been widely studied, both for their nanosize and for their magnetic characteristics [14]. In the environment, iron oxides are present naturally, but can also be chemically produced in nanoparticles of the order of 100 nm or less, which provide them with specific and better affinity for ions metals adsorption. For this reason, these nanoparticles are being used for in situ experiments [15, 16]. In environmental engineering, the application of nZVI is commonly used for the removal of metal/metalloids from polluted waters and soils, or their stabilization [17]. For example, during the remediation of contaminated soils, nZVI has become a widespread amendment for in situ applications, since it can form a permeable barrier in the soil in order to prevent the dissemination of

contaminants by the soil pore water, thus achieving their immobilization [18, 24].

Efficient nZVI remediation of groundwater contaminants has been shown in multiple studies; however, regarding nZVI-induced soil toxicity, limited data have been reported, providing preliminary results about the effects of nZVI on soil biota and some plant species [19]. Most of the reported studies have been conducted either under no real conditions or only considering

**2. Iron nanomaterials for remediation process**

available ecotoxicology data are not enough [20].

impacts.

Many metals that do not play any physiological role such as lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg) have adverse effects on human health because they have been cataloged as risk factors for the development of cancer, respiratory conditions, neurodegenerative disorders, and arthritis [5]. Lead is the most common of these toxic materials, and all Pb species are generally toxic (see **Table 1**). Volcanic activity and geochemical weathering are the greatest natural sources; man-made sources include lead-based paints, gasoline additives, food-can soldering, and battery making [6]. The movement of Pb from absorbing root hairs, is apparently impeded by several biochemical and/or physical processes involving Pb binding, inactivation, and/or precipitation [7]. Lead has accumulated in different terrestrial and aquatic ecosystems, and has been shown to accumulate in plants from several sources, including soil; however, the reports on accumulation of Pb within plants are variable [8, 9].

Arsenic is highly toxic to human health (see **Table 1**) [8, 10]. All species of As (III) and As (V) are toxic. Inorganic and most toxic forms of arsenic (arsenate and arsenite) are found in soil, crops, and water, particularly in groundwater from deep wells, often used as drinking water. These compounds are also found in environmental tobacco smoke and arsenic-treated wood, used in most outdoor wooden structures in the United States. High levels of arsenic are present in agricultural fertilizer that is used for soil treatment; as a consequence, any vegetables and fruits, if grown in this soil, will contain high levels of arsenic.

Cadmium ions, commonly found in soil and water systems, affect vital organs such as liver and kidneys (see **Table 1**) [8, 11]. This metal is considered one of the most toxic environmental substances due to its ubiquity, toxicity, and long half-life. All species of Cd are toxic. Exposure to cadmium occurs through inhalation (particularly in active cigarette smokers), groundwater consumption, industrial exposure, and contaminated food. It causes a wide variety of toxic effects when taken up by plants such as the inhibition of several plant physiological processes like oxidative reactions and nitrogen metabolism [12, 13]. Currently, there are many traditional chemical methods to remove these heavy metals from contaminated sites such as alkaline precipitation,


**Table 1.** Major sources of As, Cd, and Pb and their effect on human health [8].

ion exchange columns, electrochemical removal, filtration, and membrane technologies [8], but these methods are expensive and use many equipments to efficiently remove the contaminants. On the other hand, following the principles of Green Chemistry is necessary to use alternative products that prevent waste after remediation process, use less hazardous chemical synthesis, and minimize energy requirements of all chemical processes and environmental and economic impacts.

#### **2. Iron nanomaterials for remediation process**

landfills, electroplating, metal processing, textile, petroleum refining, pesticides, battery and paint manufacturing, and printing and photographic industries release these metals into the

Many metals that do not play any physiological role such as lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg) have adverse effects on human health because they have been cataloged as risk factors for the development of cancer, respiratory conditions, neurodegenerative disorders, and arthritis [5]. Lead is the most common of these toxic materials, and all Pb species are generally toxic (see **Table 1**). Volcanic activity and geochemical weathering are the greatest natural sources; man-made sources include lead-based paints, gasoline additives, food-can soldering, and battery making [6]. The movement of Pb from absorbing root hairs, is apparently impeded by several biochemical and/or physical processes involving Pb binding, inactivation, and/or precipitation [7]. Lead has accumulated in different terrestrial and aquatic ecosystems, and has been shown to accumulate in plants from several sources, including soil; however, the reports on accumulation of Pb within plants are variable [8, 9].

Arsenic is highly toxic to human health (see **Table 1**) [8, 10]. All species of As (III) and As (V) are toxic. Inorganic and most toxic forms of arsenic (arsenate and arsenite) are found in soil, crops, and water, particularly in groundwater from deep wells, often used as drinking water. These compounds are also found in environmental tobacco smoke and arsenic-treated wood, used in most outdoor wooden structures in the United States. High levels of arsenic are present in agricultural fertilizer that is used for soil treatment; as a consequence, any vegetables

Cadmium ions, commonly found in soil and water systems, affect vital organs such as liver and kidneys (see **Table 1**) [8, 11]. This metal is considered one of the most toxic environmental substances due to its ubiquity, toxicity, and long half-life. All species of Cd are toxic. Exposure to cadmium occurs through inhalation (particularly in active cigarette smokers), groundwater consumption, industrial exposure, and contaminated food. It causes a wide variety of toxic effects when taken up by plants such as the inhibition of several plant physiological processes like oxidative reactions and nitrogen metabolism [12, 13]. Currently, there are many traditional chemical methods to remove these heavy metals from contaminated sites such as alkaline precipitation,

**Pollutants Major sources Effect on human health Permissible level (mg/l)**

liver, and kidney

Bronchitis, dermatitis, poisoning 0.02

0.06

0.1

Renal dysfunction, lung disease, lung cancer, bone defects, increased blood pressure, kidney damage, bronchitis, gastrointestinal disorder, bone marrow, and cancer

Mental retardation in children, developmental delay, fatal infant encephalopathy, congenital paralysis, damage to the nervous system,

and fruits, if grown in this soil, will contain high levels of arsenic.

Arsenic Pesticides, fungicides, metal smelters

> pesticide, fertilizer, Cd, and Ni batteries, and nuclear

**Table 1.** Major sources of As, Cd, and Pb and their effect on human health [8].

automobile, emission, mining, and burning of coal

Cadmium Welding, electroplating,

136 Green Chemistry

fission plant

Lead Paint, pesticide, smoking,

environment. Heavy metals can persist for a long time in the environment [4].

Iron nanoparticles are a new generation of materials for environmental remediation. Various metallic ions, including Pb2+, Cr6+, Ni2+, As3+, As5+, Cd2+, Cu2+, Zn2+, and Ba2+ have been fixated from water using this new technology [14]. In situ remediation strategies are useful to reduce the mobile fraction of metals and metalloids in the soil that could reach the groundwater or be taken up by soil organisms. As such, several strategies have been used to promote the immobilization of metals in soil [15]. In the course of developing suitable options to remove heavy metal contaminants from wastewater, nanoscale zero valent iron (nZVI) particles have been found to be an alternative approach to reduce the concentration of several kinds of contaminants, mainly targeting chlorinated organic contaminants, inorganic anions, metals, and metalloids [15–19]. Although the benefits of this strategy are evident, governments and environmental agencies must evaluate any associated environmental risks because currently available ecotoxicology data are not enough [20].

Previous column experiments have showed the effectiveness of nZVI for the in situ immobilization of heavy metals, which reduces their potential leachability, as a strategy to prevent their transport into deeper soil layers, rivers, and groundwater [21]. Iron nanoparticles are particularly attractive for environmental remediation because these are much more reactive than iron powders and they can be suspended in slurry and moved to the polluted site [22, 23]. Recently, the synthesis and utilization of iron-based nanomaterials with novel properties and functions have been widely studied, both for their nanosize and for their magnetic characteristics [14]. In the environment, iron oxides are present naturally, but can also be chemically produced in nanoparticles of the order of 100 nm or less, which provide them with specific and better affinity for ions metals adsorption. For this reason, these nanoparticles are being used for in situ experiments [15, 16]. In environmental engineering, the application of nZVI is commonly used for the removal of metal/metalloids from polluted waters and soils, or their stabilization [17]. For example, during the remediation of contaminated soils, nZVI has become a widespread amendment for in situ applications, since it can form a permeable barrier in the soil in order to prevent the dissemination of contaminants by the soil pore water, thus achieving their immobilization [18, 24].

Efficient nZVI remediation of groundwater contaminants has been shown in multiple studies; however, regarding nZVI-induced soil toxicity, limited data have been reported, providing preliminary results about the effects of nZVI on soil biota and some plant species [19]. Most of the reported studies have been conducted either under no real conditions or only considering short-term exposure. Therefore, the impact of nZVI treatment on soil properties and functionality remains unclear. On the other hand, very few investigations of nZVI materials present a detailed study of the products formed in the remediation process for reusability of these nZVI after treatment [25–27]. An alternative use of the remediation product of nZVI could be for photoelectrochemical solar cells (PSC) applications.

after treatment with nZVI. For this reason, a structural analysis of used nZVI was deemed imperative to gain an understanding of the interactions between the nZVI and cadmium. This new knowledge may serve to optimize the remediation process and to provide alternative uses for the remediation product. The formations of unexpected nanofibers and cadmium ferrite structures have been reported. This remediation product or environmental waste has been suggested as a photocatalyst material that has great potential application for light harvesting [40]. These results could be useful because we can prevent the waste formation after chemical process, and reuse the products of remediation processes for other energy applications. This will decrease the amount of new hazardous substances produced after water decontamination

Nanoscale Zero Valent Iron for Environmental Cadmium Metal Treatment

A structural model of Cd-nZVI fibers is illustrated in **Figure 1**. This conceptual model of Fe<sup>0</sup> nanofibers was presented considering the results of X-ray diffraction patterns, X-photoelectron spectroscopy results, X-ray absorption spectroscopy, and high-resolution transmission elec-

O3

and FeOOH surrounding small quantities of Fe<sup>0</sup>

, and Fe<sup>0</sup>

, and FeOOH allowing the possible formation of cadmium ferrite.

sented in **Figure 1C**, cadmium ions act as the limiting reagent, where the onset of the reaction

The oxyhydroxide iron (FeOOH) has a crystal structure containing tunnel-shaped cavities that run parallel to the c-axis. These sites are bound by double rows of fused octahedral, in which cadmium ions probably reside [41]. In **Figure 2a**, HRTEM images of nZVI exhibit spherical shapes and well-aligned aggregates with a diameter range between 25 and 70 nm. These clusters of nanoparticles are caused by magnetic dipole-dipole interactions of the individual particles [42]. After nZVI Cd2+ exposure, shown in **Figure 2b**, nanofibers are organized [43]. These nanofibers were possibly produced by the diffusion of absorbed Cd2+ ions through the core-shell structure [36]. In iron oxide, an electron transfer reactions between Cd2+ ions

The fiber formation as a product of nZVI in the presence of cadmium ions is possibly due to the rearrangement of the nanomaterial structure as a consequence of the adsorption process. The interactions of Cd2+ and Fe3+, particularly, possibly promote the formation of CdFe<sup>2</sup>

**Figure 1.** Conceptual model of cadmium adsorption process on nZVI nanostructures with cadmium-iron oxides on the

nanoparticles, (B) the Fe<sup>0</sup>

http://dx.doi.org/10.5772/intechopen.72737

. For the formation of the structure pre-

–H2 O,

–Cd

139

O4 ,

, and (C) Fe<sup>0</sup>

tron microscopy (HRTEM) images. **Figure 1** shows the (A) Fe<sup>0</sup>

, FeOOH, Fe<sup>2</sup>

might probably occur in the core (**Figure 2**).

O3

O4

processes.

of Cd, Fe<sup>0</sup>

and the Fe<sup>0</sup>

surface [43].

where we observe Fe<sup>2</sup>

where we observe CdFe<sup>2</sup>

, Fe<sup>2</sup> O3

In the nZVI reaction, metallic iron is oxidized in the presence of water, which can remove other metal ions from aqueous media by chemical absorption. In this process, iron oxides such as hematite (α-Fe<sup>2</sup> O3 ) are produced [27]. Hematite has been studied for catalytic applications because of the presence of active photochemical properties [28]. Even so, the application of hematite in PSC is a challenge for the scientist community because this species is highly active in UV range but not absorbed in the visible range. The aim is to employ α-Fe<sup>2</sup> O3 in commercial solar-based devices using high temperature synthesis methods for doping structures and an alternative method to produce dye-sensitized solar cells [28–31].

## **3. Nanoscale zero valent iron (nZVI) for cadmium decontamination process**

Of all the metallic contaminants, cadmium draws special attention because of its high affinity and water solubility [32]. Cadmium species have been detected in aquatic ecosystems and found to bioaccumulate in organisms in nanomolar to micromolar concentrations [33]. Efficient nZVI remediations of groundwater contaminants have been shown in multiple studies [33–37]. However, in the literature, there is a lack of comparable studies for different nZVI materials and deployment strategies [38].

Various adsorption and kinetic models to describe metal adsorption on nZVI and Cd-nZVI surfaces using SEM/EDX and XPS measurements have been studied [26, 38] but, to our knowledge, the interactions between surface Fe<sup>0</sup> and other heavy metals in particular Cd2+ and subsequent cadmium retention in nZVI particles have not been the subject of detailed study.

Results from our study provide important information of the products formed during the remediation process of cadmium. Studies of redox and adsorption processes after treatment of nZVI have been evaluated [39]. However, it is necessary to understand in detail what occurs in the cadmium adsorption process at the nanoparticle surface. The reduction potential of Cd is larger than standard reduction potential (Eo ) of nZVI (−0.40 V, 25°C, −0.447 V), respectively [26]. Our data suggest that Cd2+ ions are sequestrated on nZVI by adsorption process [27].

Results of the Cd concentration reduction on nZVI sample were analyzed using an inductively coupled plasma (ICP). The maximum cadmium adsorption percentage relative to the initial Cd2+ concentration of 6 ppm was 93%. This percentage was obtained after a period of 5 h, which indicates that longer interaction times between cadmium ions and nZVI promoted larger cadmium concentration reduction.

These results show that nZVI is an alternative to decrease high Cd concentration in contaminated sites. However, there are no sufficient data about the possible formation of toxic product after treatment with nZVI. For this reason, a structural analysis of used nZVI was deemed imperative to gain an understanding of the interactions between the nZVI and cadmium. This new knowledge may serve to optimize the remediation process and to provide alternative uses for the remediation product. The formations of unexpected nanofibers and cadmium ferrite structures have been reported. This remediation product or environmental waste has been suggested as a photocatalyst material that has great potential application for light harvesting [40]. These results could be useful because we can prevent the waste formation after chemical process, and reuse the products of remediation processes for other energy applications. This will decrease the amount of new hazardous substances produced after water decontamination processes.

short-term exposure. Therefore, the impact of nZVI treatment on soil properties and functionality remains unclear. On the other hand, very few investigations of nZVI materials present a detailed study of the products formed in the remediation process for reusability of these nZVI after treatment [25–27]. An alternative use of the remediation product of nZVI could be for

In the nZVI reaction, metallic iron is oxidized in the presence of water, which can remove other metal ions from aqueous media by chemical absorption. In this process, iron oxides

tions because of the presence of active photochemical properties [28]. Even so, the application of hematite in PSC is a challenge for the scientist community because this species is highly

mercial solar-based devices using high temperature synthesis methods for doping structures

Of all the metallic contaminants, cadmium draws special attention because of its high affinity and water solubility [32]. Cadmium species have been detected in aquatic ecosystems and found to bioaccumulate in organisms in nanomolar to micromolar concentrations [33]. Efficient nZVI remediations of groundwater contaminants have been shown in multiple studies [33–37]. However, in the literature, there is a lack of comparable studies for different nZVI

Various adsorption and kinetic models to describe metal adsorption on nZVI and Cd-nZVI surfaces using SEM/EDX and XPS measurements have been studied [26, 38] but, to our knowl-

Results from our study provide important information of the products formed during the remediation process of cadmium. Studies of redox and adsorption processes after treatment of nZVI have been evaluated [39]. However, it is necessary to understand in detail what occurs in the cadmium adsorption process at the nanoparticle surface. The reduction potential of Cd

sequent cadmium retention in nZVI particles have not been the subject of detailed study.

[26]. Our data suggest that Cd2+ ions are sequestrated on nZVI by adsorption process [27].

Results of the Cd concentration reduction on nZVI sample were analyzed using an inductively coupled plasma (ICP). The maximum cadmium adsorption percentage relative to the initial Cd2+ concentration of 6 ppm was 93%. This percentage was obtained after a period of 5 h, which indicates that longer interaction times between cadmium ions and nZVI promoted

These results show that nZVI is an alternative to decrease high Cd concentration in contaminated sites. However, there are no sufficient data about the possible formation of toxic product

active in UV range but not absorbed in the visible range. The aim is to employ α-Fe<sup>2</sup>

**3. Nanoscale zero valent iron (nZVI) for cadmium decontamination** 

and an alternative method to produce dye-sensitized solar cells [28–31].

) are produced [27]. Hematite has been studied for catalytic applica-

and other heavy metals in particular Cd2+ and sub-

) of nZVI (−0.40 V, 25°C, −0.447 V), respectively

O3

in com-

photoelectrochemical solar cells (PSC) applications.

O3

materials and deployment strategies [38].

edge, the interactions between surface Fe<sup>0</sup>

is larger than standard reduction potential (Eo

larger cadmium concentration reduction.

such as hematite (α-Fe<sup>2</sup>

**process**

138 Green Chemistry

A structural model of Cd-nZVI fibers is illustrated in **Figure 1**. This conceptual model of Fe<sup>0</sup> nanofibers was presented considering the results of X-ray diffraction patterns, X-photoelectron spectroscopy results, X-ray absorption spectroscopy, and high-resolution transmission electron microscopy (HRTEM) images. **Figure 1** shows the (A) Fe<sup>0</sup> nanoparticles, (B) the Fe<sup>0</sup> –H2 O, where we observe Fe<sup>2</sup> O3 and FeOOH surrounding small quantities of Fe<sup>0</sup> , and (C) Fe<sup>0</sup> –Cd where we observe CdFe<sup>2</sup> O4 , FeOOH, Fe<sup>2</sup> O3 , and Fe<sup>0</sup> . For the formation of the structure presented in **Figure 1C**, cadmium ions act as the limiting reagent, where the onset of the reaction of Cd, Fe<sup>0</sup> , Fe<sup>2</sup> O3 , and FeOOH allowing the possible formation of cadmium ferrite.

The oxyhydroxide iron (FeOOH) has a crystal structure containing tunnel-shaped cavities that run parallel to the c-axis. These sites are bound by double rows of fused octahedral, in which cadmium ions probably reside [41]. In **Figure 2a**, HRTEM images of nZVI exhibit spherical shapes and well-aligned aggregates with a diameter range between 25 and 70 nm.

These clusters of nanoparticles are caused by magnetic dipole-dipole interactions of the individual particles [42]. After nZVI Cd2+ exposure, shown in **Figure 2b**, nanofibers are organized [43]. These nanofibers were possibly produced by the diffusion of absorbed Cd2+ ions through the core-shell structure [36]. In iron oxide, an electron transfer reactions between Cd2+ ions and the Fe<sup>0</sup> might probably occur in the core (**Figure 2**).

The fiber formation as a product of nZVI in the presence of cadmium ions is possibly due to the rearrangement of the nanomaterial structure as a consequence of the adsorption process. The interactions of Cd2+ and Fe3+, particularly, possibly promote the formation of CdFe<sup>2</sup> O4 ,

**Figure 1.** Conceptual model of cadmium adsorption process on nZVI nanostructures with cadmium-iron oxides on the surface [43].

The charge on the semiconductor side is distributed in the interior of the semiconductor, creating a space charge region. If the junction of the semiconductor-electrolyte is illuminated with a light having energy greater than the semiconductor bandgap, photogenerated electron-hole pairs are separated in the space charge region [48, 49]. The photogenerated minority carriers arrive at the interface of the semiconductor-electrolyte where a redox reaction will occur.

Photoelectrochemical cells, such as those produced by Brian O'Regan and Michael Grätzel, have been of interest to scientist because of their low manufacturing cost [44]. Photoelectrochemical devices require exhaustive optimization of their quantum conversion efficiency, which is

[31]. Methods such as doping with other metals and changing the structural arrangement of the system have been employed to overcome challenges regarding electron transfer processes [28]. The incorporation of Cd ions on the surface of the oxidized nZVI may produce

recent reports, this surface process may occur without using high-temperature processes, a common surface reaction described in the literature [29, 30]. Moreover, photovoltaic and

shown the use of heavy metal doped ferrite particles as semiconductors in photovoltaic and photoelectrochemical devices [30, 50–52]. Recently, the use of Cd2+ ions exposed nZVI as semiconductors in PSCs has been reported. Brian O'Regan and Michael Grätzel reported similar systems in the 1990s, which caught the attention of the scientific community due to

Photoelectrochemical devices are challenging due to the optimization of their quantum conversion efficiency, which is affected by the electron transfer processes in the system. In our study, nZVI was exposed to different Cd2+ concentrations (1–30 ppm), similar to values found in contaminated areas of Puerto Rico. The novelty of these results was to analyze the material produced after the Cd decontamination processes in water using nZVI as a photoactive substance. The product formed exhibited capable photoactive behavior for photoelectrochemical

In **Figure 3**, incident to photocurrent efficiency (IPCE) normalized signals of two PSCs are observed, each one with different material in the photoanode [54]. The samples prepared using the nZVI do not display significant signals (lowest curve). Particles treated with 30 ppm Cd2+ solution, however, exhibit a relative broadband from approximately 300–450 nm (black curve). This region is similar to the absorption results obtained in the UV/Vis analysis. Such a high photovoltage can be explained by an improvement in the electron transfer dynamics of the material in the PSC at higher cadmium concentrations due to structural changes as previously suggested in the literature [30]. As one of the principle of Green Chemistry, these results provide a new alternative to reuse nanomaterials used in decontamination processes and generate modified iron oxide photocatalyst without using high temperature. These data

have a significant value for future applications in photoactive materials synthesis.

O3

Oy

. However, few reports have

has been evaluated to produce dye-sensitized solar cells

Nanoscale Zero Valent Iron for Environmental Cadmium Metal Treatment

http://dx.doi.org/10.5772/intechopen.72737

O4

may be present at the surface of the nanoparticles [43]. As described in

[27]. Using

141

and the for-

In the nanoscale iron reaction with water, metallic iron is oxidized to α-Fe<sup>2</sup>

surface structure changes. It has been found that oxide structures such as Fex

photoelectrochemical processes have been studied with CdFe<sup>2</sup>

affected by the electron transfer processes.

as an alternative of TiO2

O4

their low cost of fabrication [53].

solar cell applications.

α-Fe<sup>2</sup> O3

mation of CdFe<sup>2</sup>

**Figure 2.** HRTEM images of (a) nZVI particles synthesized and (b) iron nanofibers formed during the cadmium ion remediation process. (c) Conceptual model representing the Cd2+ atoms interaction in Fe<sup>0</sup> core of nZVI [43].

which is in accordance with what is reported in the literature; these results show fiber formation analogous to previous studies with CdFe<sup>2</sup> O4 particles synthesized by a coprecipitation method [41]. These studies in HRTEM presented the aggregation of fine particles of CdFe<sup>2</sup> O4 having two kinds of shapes, fibrous and granular. The unintended formation of CdFe<sup>2</sup> O4 nanofibers as a remediation product presents an opportunity to reuse the remediation products for applications pertaining to light harvesting.

#### **4. Applications of nZVI in photoelectrochemical solar cell devices**

Photoelectrochemical solar cells use light to carry out a chemical reaction, converting light to chemical energy or power [44–46]. A photoelectrochemical cell is a photocurrent-generating device that has a semiconductor in contact with an electrolyte. It consists of a photoactive semiconductor working electrode (either n-type or p-type) and counter electrode made of either metal (e.g., Pt or C) or semiconductor. These electrodes are immersed in the electrolyte containing redox species with its standard potential being within the semiconductor bandgap potential region. In a metal-electrolyte junction, the potential drop occurs entirely on the solution site, whereas in a semiconductor-electrolyte junction, the potential drop occurs on the semiconductor site as well as the solution site [47].

The charge on the semiconductor side is distributed in the interior of the semiconductor, creating a space charge region. If the junction of the semiconductor-electrolyte is illuminated with a light having energy greater than the semiconductor bandgap, photogenerated electron-hole pairs are separated in the space charge region [48, 49]. The photogenerated minority carriers arrive at the interface of the semiconductor-electrolyte where a redox reaction will occur.

Photoelectrochemical cells, such as those produced by Brian O'Regan and Michael Grätzel, have been of interest to scientist because of their low manufacturing cost [44]. Photoelectrochemical devices require exhaustive optimization of their quantum conversion efficiency, which is affected by the electron transfer processes.

In the nanoscale iron reaction with water, metallic iron is oxidized to α-Fe<sup>2</sup> O3 [27]. Using α-Fe<sup>2</sup> O3 as an alternative of TiO2 has been evaluated to produce dye-sensitized solar cells [31]. Methods such as doping with other metals and changing the structural arrangement of the system have been employed to overcome challenges regarding electron transfer processes [28]. The incorporation of Cd ions on the surface of the oxidized nZVI may produce surface structure changes. It has been found that oxide structures such as Fex Oy and the formation of CdFe<sup>2</sup> O4 may be present at the surface of the nanoparticles [43]. As described in recent reports, this surface process may occur without using high-temperature processes, a common surface reaction described in the literature [29, 30]. Moreover, photovoltaic and photoelectrochemical processes have been studied with CdFe<sup>2</sup> O4 . However, few reports have shown the use of heavy metal doped ferrite particles as semiconductors in photovoltaic and photoelectrochemical devices [30, 50–52]. Recently, the use of Cd2+ ions exposed nZVI as semiconductors in PSCs has been reported. Brian O'Regan and Michael Grätzel reported similar systems in the 1990s, which caught the attention of the scientific community due to their low cost of fabrication [53].

Photoelectrochemical devices are challenging due to the optimization of their quantum conversion efficiency, which is affected by the electron transfer processes in the system. In our study, nZVI was exposed to different Cd2+ concentrations (1–30 ppm), similar to values found in contaminated areas of Puerto Rico. The novelty of these results was to analyze the material produced after the Cd decontamination processes in water using nZVI as a photoactive substance. The product formed exhibited capable photoactive behavior for photoelectrochemical solar cell applications.

which is in accordance with what is reported in the literature; these results show fiber forma-

**Figure 2.** HRTEM images of (a) nZVI particles synthesized and (b) iron nanofibers formed during the cadmium ion

remediation process. (c) Conceptual model representing the Cd2+ atoms interaction in Fe<sup>0</sup>

method [41]. These studies in HRTEM presented the aggregation of fine particles of CdFe<sup>2</sup>

having two kinds of shapes, fibrous and granular. The unintended formation of CdFe<sup>2</sup>

**4. Applications of nZVI in photoelectrochemical solar cell devices**

nanofibers as a remediation product presents an opportunity to reuse the remediation prod-

Photoelectrochemical solar cells use light to carry out a chemical reaction, converting light to chemical energy or power [44–46]. A photoelectrochemical cell is a photocurrent-generating device that has a semiconductor in contact with an electrolyte. It consists of a photoactive semiconductor working electrode (either n-type or p-type) and counter electrode made of either metal (e.g., Pt or C) or semiconductor. These electrodes are immersed in the electrolyte containing redox species with its standard potential being within the semiconductor bandgap potential region. In a metal-electrolyte junction, the potential drop occurs entirely on the solution site, whereas in a semiconductor-electrolyte junction, the potential drop occurs on the

O4

particles synthesized by a coprecipitation

core of nZVI [43].

O4

O4

tion analogous to previous studies with CdFe<sup>2</sup>

140 Green Chemistry

ucts for applications pertaining to light harvesting.

semiconductor site as well as the solution site [47].

In **Figure 3**, incident to photocurrent efficiency (IPCE) normalized signals of two PSCs are observed, each one with different material in the photoanode [54]. The samples prepared using the nZVI do not display significant signals (lowest curve). Particles treated with 30 ppm Cd2+ solution, however, exhibit a relative broadband from approximately 300–450 nm (black curve). This region is similar to the absorption results obtained in the UV/Vis analysis. Such a high photovoltage can be explained by an improvement in the electron transfer dynamics of the material in the PSC at higher cadmium concentrations due to structural changes as previously suggested in the literature [30]. As one of the principle of Green Chemistry, these results provide a new alternative to reuse nanomaterials used in decontamination processes and generate modified iron oxide photocatalyst without using high temperature. These data have a significant value for future applications in photoactive materials synthesis.

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Nanoscale Zero Valent Iron for Environmental Cadmium Metal Treatment

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143

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**Figure 3.** Graphical representation of cadmium water remediation to photoelectrochemical solar cells using nanoscale zero valent iron [54].

## **Acknowledgements**

This work was supported by NSF-CREST Center for Innovation Research and Education in Environmental Nanotechnology Grant Number 1736093.

## **Author details**

Keyla T. Soto-Hidalgo1 \* and Carlos R. Cabrera2

\*Address all correspondence to: keyla.soto@upr.edu

1 NSF-CREST Center for Innovation, Research and Education in Environmental Nanotechnology (CIRE2N), University High School, University of Puerto Rico, San Juan, Puerto Rico

2 Department of Chemistry, University of Puerto Rico, San Juan, Puerto Rico

#### **References**


**Acknowledgements**

zero valent iron [54].

142 Green Chemistry

**Author details**

Puerto Rico

**References**

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Keyla T. Soto-Hidalgo1

Environmental Nanotechnology Grant Number 1736093.

\*Address all correspondence to: keyla.soto@upr.edu

\* and Carlos R. Cabrera2

1 NSF-CREST Center for Innovation, Research and Education in Environmental

2 Department of Chemistry, University of Puerto Rico, San Juan, Puerto Rico

Nanotechnology (CIRE2N), University High School, University of Puerto Rico, San Juan,

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**Figure 3.** Graphical representation of cadmium water remediation to photoelectrochemical solar cells using nanoscale


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[44] Voloshin RA, Kreslavski VD, Zharmukhamedov SK, Bedbenov VS, Ramakrishna S, Allakhverdiev SI. Photoelectrochemical cells based on photosynthetic systems: A review.

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**Chapter 8**

**Provisional chapter**

**The Utility of the Toxic Release Inventory (TRI) in**

**The Utility of the Toxic Release Inventory (TRI) in** 

**Industrial Green Chemistry Practices in the United**

**States**

**States**

Sandra Duque Gaona

**Abstract**

reporting

**1. Introduction**

Sandra Duque Gaona

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.70716

**Tracking Implementation and Environmental Impact of**

The Toxics Release Inventory is a rich data source with nearly 30 years of reported data from industrial facilities located in the United States. Annually, these facilities report on their chemical waste management practices, including the quantities they release to air, water, and land; treat; combust for energy recovery; or recycle. Facilities are also required to disclose any green chemistry or other pollution prevention practices, and have the option to provide additional details on these practices or on barriers they encounter in implementing such practices. The Toxics Release Inventory (TRI) provides a means by which a facility's or industry sector's implementation of green chemistry practices can be tracked, and the impact that these practices have on environmental performance. This chapter describes analytical options for tracking implementation of green chemistry practices and assessing the environmental impact of such practices. Key TRI data ele-

**Keywords:** green chemistry, codes, source reduction, toxics, chemicals, TRI, releases,

ments are highlighted as well as where to obtain the information.

**Tracking Implementation and Environmental Impact** 

**of Industrial Green Chemistry Practices in the United** 

DOI: 10.5772/intechopen.70716

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

Facilities that are subject to the Toxics Release Inventory (TRI) reporting requirements are required to disclose any source reduction practices implemented at their facilities during the year for which they are reporting. Facilities report the newly implemented source reduction practices by choosing one or more predefined codes (W-codes) that correspond to a specific


**Provisional chapter**

**The Utility of the Toxic Release Inventory (TRI) in Tracking Implementation and Environmental Impact of Industrial Green Chemistry Practices in the United States Tracking Implementation and Environmental Impact of Industrial Green Chemistry Practices in the United States**

**The Utility of the Toxic Release Inventory (TRI) in** 

DOI: 10.5772/intechopen.70716

Sandra Duque Gaona Additional information is available at the end of the chapter

Sandra Duque Gaona

[45] Lewis NS, Nocera DG. Powering the planet: Chemical challenges in solar energy utilization. Proceedings of the National Academy of Sciences of the United States of America.

[46] Kamat PV. Semiconductor surface chemistry as holy grail in photocatalysis and photo-

[47] Wei D, Amaratunga G. Photoelectrochemical cell and its applications in optoelectronics.

[48] Sivula K, van de Krol R. Semiconducting materials for photoelectrochemical energy con-

[49] van de Krol R. Photoelectrochemical measurements. In: van de Krol R, Grätzel M, editors. Photoelectrochemical Hydrogen Production. Boston: Springer; 2012. pp. 69-117 [50] Harish KN, Bhojya Naik HS, Prashanth kumar PN, Viswanath R. Optical and photocatalytic properties of solar light active Nd-substituted Ni ferrite catalysts: For environmen-

tal protection. ACS Sustainable Chemistry & Engineering. 2013;**1**(9):1143-1153

[51] Harish KN, Bhojya Naik HS, Prashanth kumar PN, Viswanath R. Synthesis, enhanced optical and photocatalytic study of Cd-Zn ferrites under sunlight. Catalysis Science &

[52] Harish K, Bhojya Naik H, Prashanth Kumar P, Vishwanath R, Yashvanth Kumar G.

[53] O'Regan B, Gratzel M. A low-cost, high-efficiency solar cell based on dye-sensitized

[54] Soto Hidalgo KT, Ortiz-Quiles EO, Betancourt LE, Larios E, José-Yacaman M, Cabrera CR. Photoelectrochemical solar cells prepared from nanoscale zerovalent iron used for aqueous Cd2+ removal. ACS Sustainable Chemistry & Engineering. 2016;**4**(3):738-745

films. Nature. 1991;**353**(6346):737-740

in water treatment under solar light irradiation. Archives of Applied Science Research.

O4

nanocatalysts: Potential application

voltaics. Accounts of Chemical Research. 2017;**50**(3):527-531

version. Nature Reviews Materials. 2016;**1**:15010

Optical and photocatalytic properties of CdFe<sup>2</sup>

Technology. 2012;**2**(5):1033-1039

2013;**5**(2):42-51

colloidal TiO2

International Journal of Electrochemical Science. 2007;**2**:897-912

2006;**103**(43):15729-15735

146 Green Chemistry

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.70716

#### **Abstract**

The Toxics Release Inventory is a rich data source with nearly 30 years of reported data from industrial facilities located in the United States. Annually, these facilities report on their chemical waste management practices, including the quantities they release to air, water, and land; treat; combust for energy recovery; or recycle. Facilities are also required to disclose any green chemistry or other pollution prevention practices, and have the option to provide additional details on these practices or on barriers they encounter in implementing such practices. The Toxics Release Inventory (TRI) provides a means by which a facility's or industry sector's implementation of green chemistry practices can be tracked, and the impact that these practices have on environmental performance. This chapter describes analytical options for tracking implementation of green chemistry practices and assessing the environmental impact of such practices. Key TRI data elements are highlighted as well as where to obtain the information.

**Keywords:** green chemistry, codes, source reduction, toxics, chemicals, TRI, releases, reporting

#### **1. Introduction**

Facilities that are subject to the Toxics Release Inventory (TRI) reporting requirements are required to disclose any source reduction practices implemented at their facilities during the year for which they are reporting. Facilities report the newly implemented source reduction practices by choosing one or more predefined codes (W-codes) that correspond to a specific

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

practice within the eight established TRI source reduction categories (e.g., process modifications, substitution of raw materials).

Over the past 2 decades many facilities have implemented green chemistry practices in their operations that reduce or eliminate the use or generation of TRI-listed chemicals to prevent pollution at its source. In doing so, facilities improve their environmental performance while off-setting the continually rising costs of managing production-related toxic chemical wastes. Beginning with the 2012 TRI reporting year, in recognizing that none of the existing source reduction codes (W-codes) were specific to green chemistry, the U.S. Environmental Protection Agency (EPA) implemented six new codes to align closely with green chemistry practices (e.g., W15, introduced in-line product quality monitoring or other process analysis system and W43, substituted a feedstock or reagent chemical with a different chemical), to enable facilities to disclose adoption of these practices.

This chapter introduces the EPA's TRI program and how the TRI has evolved over the past 30 years into a pollution prevention resource. TRI data specific to source reduction will be described, followed by discussions on how these data can be used to assess industrial progress in implementing green chemistry practices and possible impacts on the reduction of TRI-listed chemical generation and releases to the environment.

#### **2. Toxics Release Inventory (TRI) Program**

The TRI program was established by the Emergency Planning and Community Right-to-Know Act (EPCRA) in 1986 [1], and TRI reporting commenced with the 1987 reporting year (first TRI reports due July 1st, 1988), and has continued to the present. The 2015 reporting year marked 29 years of available TRI data, resulting in a rich source of information on TRI-listed chemicals, which now exceeds over 650 discrete chemicals and 30 chemical categories [2].

For reporting year 2012, the TRI program, cognizant of the advancements in science and initiatives underway at facilities, expanded the codes available to facilities under the source reduction categories to better align with green chemistry practices. The addition of these six

Source Reduction

The Utility of the Toxic Release Inventory (TRI) in Tracking Implementation and Environmental…

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149

Recycling

Energy Recovery

Treatment

Disposal or Other Releases

Less Preferable

During this same time frame, the program made additional enhancements to the reporting form allowing facilities the option to specify barriers that were preventing them from implementing source reduction activities. Previously, facilities only had the opportunity to provide

Of greatest value perhaps to TRI data users are the open text data fields. Facilities (since 1991) can provide additional optional commentary to describe their source reduction activities, other environmental practices, or other activities reported to the TRI program such as reasons for increased releases. This field has the potential to be an important communication mechanism if used by industry. For this reason, the TRI encourages the submittal of optional information, for it not only augments understanding of industrial management, but provides a unique opportunity for facilities to showcase and further extend successful pollution pre-

Facilities have had the option to report on pollution prevention activities since the start of the TRI program. For the first 4 years (1987–1990) of the program, prior to implementation of the additional TRI reporting requirements established under the PPA, facilities could voluntarily

new codes is discussed in greater detail in the next section.

More

**Figure 1.** Waste management hierarchy.

Preferable

vention practices.

**2.1. Evolution of the TRI reporting form**

commentary without adequate data fields for tracking purposes.

The Pollution Prevention Act (PPA) of 1990 expanded TRI's authority to collect information beyond release quantities as specified in EPCRA Section 313 to include information specific to source reduction and preferred waste management techniques as described under Section 6607 of the PPA [3]. This change was significant giving the public a broader lens by which to evaluate and track corporate performance in their management of TRI-listed chemicals.

As illustrated in (**Figure 1**), the waste management hierarchy [4], since reporting year 1991, for a given chemical on the TRI list, facilities are *required* to report the quantities of the chemical recycled, used for energy recovery, or treated at the facility or elsewhere in addition to the original reporting requirements on releases emitted directly into the environment or transferred off-site to disposal, treatment, or storage facilities. Optional waste minimization information also transitions to a formal requirement where facilities must report any source reduction activities (e.g., process modifications, substitution of raw materials) newly implemented at the facility during the reporting year.

The Utility of the Toxic Release Inventory (TRI) in Tracking Implementation and Environmental… http://dx.doi.org/10.5772/intechopen.70716 149

**Figure 1.** Waste management hierarchy.

practice within the eight established TRI source reduction categories (e.g., process modifica-

Over the past 2 decades many facilities have implemented green chemistry practices in their operations that reduce or eliminate the use or generation of TRI-listed chemicals to prevent pollution at its source. In doing so, facilities improve their environmental performance while off-setting the continually rising costs of managing production-related toxic chemical wastes. Beginning with the 2012 TRI reporting year, in recognizing that none of the existing source reduction codes (W-codes) were specific to green chemistry, the U.S. Environmental Protection Agency (EPA) implemented six new codes to align closely with green chemistry practices (e.g., W15, introduced in-line product quality monitoring or other process analysis system and W43, substituted a feedstock or reagent chemical with a different chemical), to

This chapter introduces the EPA's TRI program and how the TRI has evolved over the past 30 years into a pollution prevention resource. TRI data specific to source reduction will be described, followed by discussions on how these data can be used to assess industrial progress in implementing green chemistry practices and possible impacts on the reduction of

The TRI program was established by the Emergency Planning and Community Right-to-Know Act (EPCRA) in 1986 [1], and TRI reporting commenced with the 1987 reporting year (first TRI reports due July 1st, 1988), and has continued to the present. The 2015 reporting year marked 29 years of available TRI data, resulting in a rich source of information on TRI-listed chemicals, which now exceeds over 650 discrete chemicals and 30 chemical

The Pollution Prevention Act (PPA) of 1990 expanded TRI's authority to collect information beyond release quantities as specified in EPCRA Section 313 to include information specific to source reduction and preferred waste management techniques as described under Section 6607 of the PPA [3]. This change was significant giving the public a broader lens by which to evaluate and track corporate performance in their management of TRI-listed

As illustrated in (**Figure 1**), the waste management hierarchy [4], since reporting year 1991, for a given chemical on the TRI list, facilities are *required* to report the quantities of the chemical recycled, used for energy recovery, or treated at the facility or elsewhere in addition to the original reporting requirements on releases emitted directly into the environment or transferred off-site to disposal, treatment, or storage facilities. Optional waste minimization information also transitions to a formal requirement where facilities must report any source reduction activities (e.g., process modifications, substitution of raw materials) newly imple-

tions, substitution of raw materials).

148 Green Chemistry

enable facilities to disclose adoption of these practices.

**2. Toxics Release Inventory (TRI) Program**

mented at the facility during the reporting year.

categories [2].

chemicals.

TRI-listed chemical generation and releases to the environment.

For reporting year 2012, the TRI program, cognizant of the advancements in science and initiatives underway at facilities, expanded the codes available to facilities under the source reduction categories to better align with green chemistry practices. The addition of these six new codes is discussed in greater detail in the next section.

During this same time frame, the program made additional enhancements to the reporting form allowing facilities the option to specify barriers that were preventing them from implementing source reduction activities. Previously, facilities only had the opportunity to provide commentary without adequate data fields for tracking purposes.

Of greatest value perhaps to TRI data users are the open text data fields. Facilities (since 1991) can provide additional optional commentary to describe their source reduction activities, other environmental practices, or other activities reported to the TRI program such as reasons for increased releases. This field has the potential to be an important communication mechanism if used by industry. For this reason, the TRI encourages the submittal of optional information, for it not only augments understanding of industrial management, but provides a unique opportunity for facilities to showcase and further extend successful pollution prevention practices.

#### **2.1. Evolution of the TRI reporting form**

Facilities have had the option to report on pollution prevention activities since the start of the TRI program. For the first 4 years (1987–1990) of the program, prior to implementation of the additional TRI reporting requirements established under the PPA, facilities could voluntarily provide information on waste minimization (pollution prevention) through the selection of one of eight codes shown in **Table 1** that best described their activities. Facilities could also indicate the effect of these activities on the quantities released by providing a waste minimization index helping to distinguish between business activities and minimization efforts. However, this optional data collected in Section 8 of the TRI form was highly underreported. Note that recycling was included within this category and later separated [5].

**Source reduction category**

Good operating practices

Inventory control

Spill and leak prevention

Raw material modifications

Process modifications **Source reduction code**

**Source reduction description**

W19 Other changes made in operating practices

W23 Eliminated shelf-life requirements for stable

W24 Instituted better labeling procedures

W29 Other changes made in inventory control

W31 Improved storage or stacking procedures

W33 Installed overflow alarms or automatic

transfer operations

W35 Installed vapor recovery systems

W41 Increased purity of raw materials

W53 Used a different process catalyst

W58 Other process modifications made

W49 Other raw material modifications made

W51 Instituted re-circulation within a process W52 Modified equipment, layout, or piping

discarding of empty containers

discarding of empty containers

shutoff valves

leak sources

W42 Substituted raw materials

W32 Improved procedures for loading, unloading, and

W39 Other changes made in spill and leak prevention

or procedures

changeovers

beyond shelf-life

still effective

materials

be discarded

W13 Improved maintenance scheduling, record keeping,

W22 Began to test outdated material — continue to use if

W14 Changed production schedule to minimize equipment and feedstock

The Utility of the Toxic Release Inventory (TRI) in Tracking Implementation and Environmental…

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151

W21 Instituted procedures to ensure that materials do not stay in inventory

W25 Instituted clearinghouse to exchange materials that would otherwise

W36 Implemented inspection or monitoring program of potential spill or

W54 Instituted better controls on operating bulk containers to minimize

W55 Changed from small volume containers to bulk containers to minimize


**Table 1.** Pre-PPA codes, waste minimization codes.

Recognizing the importance of this information as a possible way to address chemical wastes and operations at industrial facilities, regulators significantly expanded Section 8 of the TRI reporting form (Form R) and made mandatory the reporting of pollution prevention (P2) activities as of reporting year 1991. Source reduction activities implemented during a year would be reported through the selection of the appropriate code(s) indicating the type of actions taken to reduce chemical waste: disposed of or released, treated, used for energy recovery, or recycled. Facilities could select from the 43 codes listed in **Table 2** that correspond to eight source reduction categories [6].

The expanded Section 8 of the TRI Form R also includes other reporting requirements specified by the PPA on quantities of chemical waste managed as waste (which includes recycled, burned for energy recovery, treated, or released). This section often represents a summary of more detailed information presented in other sections, such as releases in Sections 5 and 6 or on-site treatment methods and efficiencies in Section 7. Beyond the additional report data elements, following the PPA, the reporting form was reorganized and condensed into two parts, combining previous Parts II and III into the current Part II on Chemical Information.

provide information on waste minimization (pollution prevention) through the selection of one of eight codes shown in **Table 1** that best described their activities. Facilities could also indicate the effect of these activities on the quantities released by providing a waste minimization index helping to distinguish between business activities and minimization efforts. However, this optional data collected in Section 8 of the TRI form was highly underreported.

M1 Recycling/reuse on-site Solvent recovery still; vapor recovery systems; reuse of materials in a process M2 Recycling/reuse off-site Commercial recycler; toll recycling; at an off-site company-owned facility M3 Equipment/technology modifications Change from solvent to mechanical stripping; modify spray

M4 Process procedure modifications Change production schedule to minimize equipment and

M5 Reformulation/redesign of product Change in product specifications; modify design or composition;

M6 Substitution of raw materials Change or eliminate additives; substitute water-based for solvent-

raw materials

minimization

M8 Other waste minimization technique Elimination of process; discontinuation of product

reduce or modify packaging

systems to reduce overspray losses; install floating roofs to reduce tank emissions; install float guards to prevent tank overflow

feedstock change-overs; improved control of operating conditions;

based coating materials, cleaners, and pigments; increase purity of

After maintenance frequency; institute leak detection program; improved inventory control; institute training program on waste

segregation of wastes to permit recycling

Recognizing the importance of this information as a possible way to address chemical wastes and operations at industrial facilities, regulators significantly expanded Section 8 of the TRI reporting form (Form R) and made mandatory the reporting of pollution prevention (P2) activities as of reporting year 1991. Source reduction activities implemented during a year would be reported through the selection of the appropriate code(s) indicating the type of actions taken to reduce chemical waste: disposed of or released, treated, used for energy recovery, or recycled. Facilities could select from the 43 codes listed in **Table 2** that correspond

The expanded Section 8 of the TRI Form R also includes other reporting requirements specified by the PPA on quantities of chemical waste managed as waste (which includes recycled, burned for energy recovery, treated, or released). This section often represents a summary of more detailed information presented in other sections, such as releases in Sections 5 and 6 or on-site treatment methods and efficiencies in Section 7. Beyond the additional report data elements, following the PPA, the reporting form was reorganized and condensed into two parts,

combining previous Parts II and III into the current Part II on Chemical Information.

to eight source reduction categories [6].

**Table 1.** Pre-PPA codes, waste minimization codes.

M7 Improved housekeeping, training, inventory control

Note that recycling was included within this category and later separated [5].

**Code Description Example**

150 Green Chemistry



**2.2. TRI data elements**

**Green chemistry code**

TRI Form R Section 8.11).

production associated with the chemical.

For analytical purposes to track the implementation and impact of green chemistry practices, five overarching data elements are important. Background on source reduction has already been provided and to a lesser extent on optional pollution prevention (P2) text. These first two elements along with production information help understand the quantitative values (waste

• **Optional P2 Text**, which includes narratives on P2-related activities and provide greater context for understanding source reduction activities, other environmental management practices, as well as barriers to source reduction implementation at the facility (reported in

• **Source Reduction**, which includes newly implemented activities that reduce or eliminate the generation of pollutants (reported in TRI Form R Section 8.10). Source reduction prac-

• **Production Ratio (PR) or Activity Index (AI)**, which specifies the level of increase or decrease from the previous year, of the production process or other activity in which the toxic chemical is manufactured, processed or otherwise used (reported in TRI Form R Section 8.9). This number is usually around 1.0. For example, a production ratio or activity index of 1.5 indicates about a 50% increase in production from the prior year associated with, for example, the use of the chemical, while a value of 0.3 indicates about a 70% decrease in

tices include for example process modifications and substitution of raw materials.

managed and releases) reported for TRI-listed chemicals. These elements are:

**Green chemistry code description Barrier** 

W15 Introduced in-line product quality

analysis system

W43 Substituted a feedstock or reagent

W50 Optimized reaction conditions or

W56 Reduced or eliminated use of an organic solvent

manufacturing process

**Table 3.** Green chemistry and barrier codes added in 2012.

to replace a previous chemical

W84 Developed a new chemical product

synthesis

W57 Used biotechnology in

product

monitoring or other process

chemical with a different chemical

otherwise increased efficiency of

**code**

**Barrier code description**

The Utility of the Toxic Release Inventory (TRI) in Tracking Implementation and Environmental…

activities/initiatives

production processes

were unsuccessful

result of source reduction

B5 Specific regulatory/permit burdens

economically feasible

B8 Other barriers

B1 Insufficient capital to install new source reduction equipment or implement new source reduction

http://dx.doi.org/10.5772/intechopen.70716

153

B2 Require technical information on pollution prevention techniques applicable to specific

B3 Concern that product quality may decline as a

B4 Source reduction activities were implemented but

B6 Pollution prevention previously implemented-

B7 No known substitutes or alternative technologies

additional reduction does not appear technically or

**Table 2.** Post-PPA codes, source reduction codes.

Since 1991, the TRI Form R has been fine-tuned with smaller improvements for clarification purposes and to reduce reporting burdens. The gradual transition from 2006 to 2014 from paper form reporting to an electronic-only system, with the exception of those facilities claiming trade secret information also helped greatly with data quality and increased reporting of optional descriptive information. Moreover, significant to pollution prevention and green chemistry are the additions for the 2012 reporting year [7]. The 2012 update allows for the tracking of green chemistry activities as well as better tracking of barriers to source reduction. As explained in the introduction, six green chemistry source reduction codes were added expanding the total number of source reduction codes to 49. Noticing that facilities were providing commentary on obstacles, the TRI Program also developed eight codes that enable facilities to disclose (voluntarily) the most common barriers to source reduction implementation. These additional codes are listed in **Table 3**.


**Table 3.** Green chemistry and barrier codes added in 2012.

#### **2.2. TRI data elements**

Since 1991, the TRI Form R has been fine-tuned with smaller improvements for clarification purposes and to reduce reporting burdens. The gradual transition from 2006 to 2014 from paper form reporting to an electronic-only system, with the exception of those facilities claiming trade secret information also helped greatly with data quality and increased reporting of optional descriptive information. Moreover, significant to pollution prevention and green chemistry are the additions for the 2012 reporting year [7]. The 2012 update allows for the tracking of green chemistry activities as well as better tracking of barriers to source reduction. As explained in the introduction, six green chemistry source reduction codes were added expanding the total number of source reduction codes to 49. Noticing that facilities were providing commentary on obstacles, the TRI Program also developed eight codes that enable facilities to disclose (voluntarily) the most common barriers to source reduction implementation. These additional codes are listed in **Table 3**.

**Source reduction category**

152 Green Chemistry

Surface preparation and finishing

Product modifications

Cleaning and degreasing

**Source reduction code**

**Source reduction description**

W59 Modified stripping/cleaning equipment

other materials)

W64 Improved draining procedures

W66 Modified or installed rinse systems W67 Improved rinse equipment design W68 Improved rinse equipment operation

W72 Modified spray systems or equipment W73 Substituted coating materials used W74 Improved application techniques W75 Changed from spray to other system

W81 Changed product specifications

W89 Other product modifications made

W83 Modified packaging

**Table 2.** Post-PPA codes, source reduction codes.

W82 Modified design or composition of product

W65 Redesigned parts racks to reduce drag out

W60 Changed to mechanical stripping/cleaning devices (from solvents or

W61 Changed to aqueous cleaners (from solvents or other materials)

W63 Modified containment procedures for cleaning units

W71 Other cleaning and degreasing modifications made

W78 Other surface preparation and finishing modifications made

For analytical purposes to track the implementation and impact of green chemistry practices, five overarching data elements are important. Background on source reduction has already been provided and to a lesser extent on optional pollution prevention (P2) text. These first two elements along with production information help understand the quantitative values (waste managed and releases) reported for TRI-listed chemicals. These elements are:


• **Waste Managed**, which includes all quantities of waste that are recycled, used for energy recovery, treated, or released whether on-site or transferred off-site (reported in TRI Form R Sections 8.1 through 8.7). Waste managed tracks production-related waste only and does not include quantities associated with accidental or remedial one-time events.

are recommended. For example, to fully understand the potential impact of green chemistry practices it is important to track the set of facilities that reported green chemistry for specific chemicals over a broad time frame. Gathering pre-source reduction quantities as well as post-

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**Production levels**: Consideration should also be given to production information and whether the facility is operating within normal ranges and not below or above for the time span being considered. The reported production ratio or activity index help understand the quantitative values reported and assess whether changes (increases or decreases) are due to shifts in production levels or attributable to other factors such as the implementation of new source reduction activities. Increasing or stable production coupled with decreasing releases

**Focus on subgroups**: To more profoundly understand the magnitude of the impact, segmenting the data by industry (e.g., specific industry sector or subsector) can inform on overall activities undertaken by similar businesses. Facilities reporting to the TRI can specify up to six North American Industrial Classification System (NAICS) codes with one as the primary NAICS code, corresponding to their primary business activity. More in-depth analysis using industry-chemical combinations may also be advantageous to more accurately assess green chemistry impacts of certain chemicals or types of chemicals. Geographic analysis as an additional layer to the industry studies or as a separate subgroup option may provide some insight on local policies or clustering of mutually-beneficial resources.

The TRI dataset, while very comprehensive as a multi-media inventory of releases and other waste management information, should not be studied in isolation. Consideration of TRI in conjunction with other data sources will allow for more holistic assessment of green chemistry impacts in light of other confounding factors. For example, external factors such as outsourcing (transferring manufacturing and production operations to facilities in other countries) and the state of the economy should also be evaluated. A study published in 2015 considering this same topic of assessing the implementation and effectiveness of green chemistry in industrial manufacture of chemicals, but focused on TRI and pharmaceutical manufacturers, describes how these external factors can be considered [10]. Another valuable resource that discusses more general details on limitations of

the TRI data is EPA's document on *Factors to Consider when using TRI Data* [11].

**in the US**

**3.1. Source reduction**

*such substances, pollutants, or contaminants."*

**3. Tracking implementation of source reduction and green chemistry** 

According to the Pollution Prevention Act of 1990, source reduction is any practice that:

*"reduces the amount of any hazardous substance, pollutant, or contaminant entering any waste stream or otherwise released into the environment (including fugitive emissions) prior to recycling, treatment, or disposal; and reduces the hazards to public health and the environment associated with the release of* 

source reduction quantities would give some insight as to the impact of the change.

is a positive indicator of effective pollution prevention practices.

• **Releases**, which includes all quantities disposed of or otherwise released to the environment through all release mechanisms to all media, whether on-site or transferred off-site to a publically owned treatment works (POTWs) or other facility for disposal, treatment, or storage (reported in TRI Form R Sections 5 and 6). Release quantities track both production and non-production related releases. Releases to air include stack and fugitive emissions. Releases to land include, for example, disposal in landfills and injection into underground wells. Releases to water include discharges into rivers, streams, or other bodies of water.

#### **2.3. TRI data reporting and access**

Before delving into analytical methodologies, it's important to understand the segment of industrial activity that TRI covers. TRI represents a slice of industrial activity. The inventory collects information from larger industrial facilities that meet the TRI reporting criteria for the employee threshold, the chemical manufacture, processing or otherwise use threshold, and operate within an industry covered sector. Specifically, facilities are subject to reporting if they (1) have ten or more full-time employees, (2) are in a TRI-covered industry NAICS code such as the manufacturing sector and other sectors (e.g., electric utilities, metal mining, and hazardous waste management) or are federal facilities, and (3) manufacture or process more than 25,000 lb., or otherwise uses more than 10,000 lb. of a TRI-listed chemical within a calendar year. Thresholds for persistent bioaccumulative toxic (PBT) chemicals are lower – as low as 0.1 g for dioxin – due to their potentially greater threat to human and environmental health.

Facilities subject to the TRI reporting requirements report annually by July 1st of each year to EPA's TRI Program, and state and tribal governments [8]. Each year, EPA's TRI Program receives approximately 80,000 form reports from approximately 20,000 facilities [9]. Form reports are chemical and chemical category specific and facilities that exceed the thresholds discussed above for a specific calendar year are required to report on the data elements outlined above as well as others.

EPA makes this information available and readily accessible to the public through various data tools, maintained by EPA's TRI Program. Various access options are discussed later in the chapter.

#### **2.4. Analytical considerations and methodologies**

In order to conduct sound analysis of green chemistry activities reported to the TRI Program, certain considerations are key for tailoring the research. Three considerations are outlined below using the data that can be derived from the TRI dataset.

**Tracking a set of facilities**: Analysis of the reported quantities for waste managed and released in the year the source reduction activity was reported may not lead to any significant insight as implementation of an action may not result in immediate effects. Therefore, instead of gathering data for the specific years associated with green chemistry codes, set analyses are recommended. For example, to fully understand the potential impact of green chemistry practices it is important to track the set of facilities that reported green chemistry for specific chemicals over a broad time frame. Gathering pre-source reduction quantities as well as postsource reduction quantities would give some insight as to the impact of the change.

**Production levels**: Consideration should also be given to production information and whether the facility is operating within normal ranges and not below or above for the time span being considered. The reported production ratio or activity index help understand the quantitative values reported and assess whether changes (increases or decreases) are due to shifts in production levels or attributable to other factors such as the implementation of new source reduction activities. Increasing or stable production coupled with decreasing releases is a positive indicator of effective pollution prevention practices.

**Focus on subgroups**: To more profoundly understand the magnitude of the impact, segmenting the data by industry (e.g., specific industry sector or subsector) can inform on overall activities undertaken by similar businesses. Facilities reporting to the TRI can specify up to six North American Industrial Classification System (NAICS) codes with one as the primary NAICS code, corresponding to their primary business activity. More in-depth analysis using industry-chemical combinations may also be advantageous to more accurately assess green chemistry impacts of certain chemicals or types of chemicals. Geographic analysis as an additional layer to the industry studies or as a separate subgroup option may provide some insight on local policies or clustering of mutually-beneficial resources.

The TRI dataset, while very comprehensive as a multi-media inventory of releases and other waste management information, should not be studied in isolation. Consideration of TRI in conjunction with other data sources will allow for more holistic assessment of green chemistry impacts in light of other confounding factors. For example, external factors such as outsourcing (transferring manufacturing and production operations to facilities in other countries) and the state of the economy should also be evaluated. A study published in 2015 considering this same topic of assessing the implementation and effectiveness of green chemistry in industrial manufacture of chemicals, but focused on TRI and pharmaceutical manufacturers, describes how these external factors can be considered [10]. Another valuable resource that discusses more general details on limitations of the TRI data is EPA's document on *Factors to Consider when using TRI Data* [11].

## **3. Tracking implementation of source reduction and green chemistry in the US**

#### **3.1. Source reduction**

• **Waste Managed**, which includes all quantities of waste that are recycled, used for energy recovery, treated, or released whether on-site or transferred off-site (reported in TRI Form R Sections 8.1 through 8.7). Waste managed tracks production-related waste only and does

• **Releases**, which includes all quantities disposed of or otherwise released to the environment through all release mechanisms to all media, whether on-site or transferred off-site to a publically owned treatment works (POTWs) or other facility for disposal, treatment, or storage (reported in TRI Form R Sections 5 and 6). Release quantities track both production and non-production related releases. Releases to air include stack and fugitive emissions. Releases to land include, for example, disposal in landfills and injection into underground wells. Releases to water include discharges into rivers, streams, or other bodies of water.

Before delving into analytical methodologies, it's important to understand the segment of industrial activity that TRI covers. TRI represents a slice of industrial activity. The inventory collects information from larger industrial facilities that meet the TRI reporting criteria for the employee threshold, the chemical manufacture, processing or otherwise use threshold, and operate within an industry covered sector. Specifically, facilities are subject to reporting if they (1) have ten or more full-time employees, (2) are in a TRI-covered industry NAICS code such as the manufacturing sector and other sectors (e.g., electric utilities, metal mining, and hazardous waste management) or are federal facilities, and (3) manufacture or process more than 25,000 lb., or otherwise uses more than 10,000 lb. of a TRI-listed chemical within a calendar year. Thresholds for persistent bioaccumulative toxic (PBT) chemicals are lower – as low as 0.1 g for dioxin – due to their potentially greater threat to human and environmental health. Facilities subject to the TRI reporting requirements report annually by July 1st of each year to EPA's TRI Program, and state and tribal governments [8]. Each year, EPA's TRI Program receives approximately 80,000 form reports from approximately 20,000 facilities [9]. Form reports are chemical and chemical category specific and facilities that exceed the thresholds discussed above for a specific calendar year are required to report on the data elements outlined above as well as others. EPA makes this information available and readily accessible to the public through various data tools, maintained by EPA's TRI Program. Various access options are discussed later in the chapter.

In order to conduct sound analysis of green chemistry activities reported to the TRI Program, certain considerations are key for tailoring the research. Three considerations are outlined

**Tracking a set of facilities**: Analysis of the reported quantities for waste managed and released in the year the source reduction activity was reported may not lead to any significant insight as implementation of an action may not result in immediate effects. Therefore, instead of gathering data for the specific years associated with green chemistry codes, set analyses

not include quantities associated with accidental or remedial one-time events.

**2.3. TRI data reporting and access**

154 Green Chemistry

**2.4. Analytical considerations and methodologies**

below using the data that can be derived from the TRI dataset.

According to the Pollution Prevention Act of 1990, source reduction is any practice that:

*"reduces the amount of any hazardous substance, pollutant, or contaminant entering any waste stream or otherwise released into the environment (including fugitive emissions) prior to recycling, treatment, or disposal; and reduces the hazards to public health and the environment associated with the release of such substances, pollutants, or contaminants."*

Pollution can be reduced at its source by a wide variety of techniques, prior to end-of-pipe pollution controls or recycling, such as by changing the product, materials, or processes that generate pollution in the first place. Because of the potential advantages of these preventative approaches, the U.S. EPA took steps to encourage industrial facilities to engage in source reduction. On their part, industrial facilities have engaged in substantial pollution prevention efforts, by carrying out 447,000 unique source reduction activities between 1991 and 2015 (as reported to the EPA's TRI Program).<sup>1</sup> **Figure 2** shows that many facilities (about 107,000) conducted these source reduction projects over the past 25 years [12].

**Economy and business** benefit from reduced waste generation, eliminating costly remediation in the event of accidental releases, hazardous waste disposal, and end-of-the-pipe treatments. Implementing green chemistry saves money by offsetting the costs associated with managing toxic or hazardous chemical waste. In terms of the chemicals, it reduces the need and demand for the manufacture of TRI-listed chemicals while incentivizing the creation of less toxic or non-toxic chemicals, improving competitiveness of chemical manufacturers and their customers. Use of green chemistry and associated safer-product labeling (e.g. Safer

1,578

Process Modifications

**The environment** benefits from reduced emissions of TRI-listed chemicals or other hazardous substances, signifying less chemical disruptions to ecosystems. Through green chemistry, the environment would benefit from reductions in emissions of toxics to air, water, and land such as reduced use of landfills, especially hazardous waste landfills. Plants and animals also suffer less

**Human health** also benefits from cleaner environmental conditions. Cleaner air resulting from reductions in hazardous chemicals released to air leads to reduced respiratory disease and other illnesses. Similarly, cleaner water resulting from reductions in hazardous chemicals released to water lead to cleaner drinking and recreational water. Application of green chemistry results in safer consumer products that enter the market and are available for purchase, thereby increasing the safety of consumers and society in general. These products may be new, replacements for less safe products (e.g., certain pesticides, cleaning products), or designed to be manufactured efficiently and with less accompanying waste (e.g., drugs). This preventive practice also benefits the workers in the chemical industry resulting in increased safety through less use of toxic materials, reduced potential for exposure and accidents (e.g.,

Choice labeling) [14] may also lead to increased consumer sales (by earnings).

182

Modifications 3,002

Surface Preparation and Finishing

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163

300

686

Cleaning and Degreasing

656

Product Modifications

Spill and Leak Prevention

**Figure 3.** Number of source reduction activities.

941

Raw Material

Inventory Control

harm from reductions in hazardous chemicals entering the environment.

fires or explosions), and reduced need for personal protective equipment.

**Figure 2.** Facilities with source reduction projects.

Based on the eight source reduction categories tracked, the trend graph above shows that the most reported source reduction category is good operating practices. Source reduction data reported for 2015 (**Figure 3**) show that good operating practices represents 40% followed by the process modifications category at 21%. The two least reported categories are surface preparation and finishing as well as cleaning and degreasing.

#### **3.2. Green chemistry**

According to the U.S. EPA, "Green chemistry is the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances. Green chemistry applies across the life cycle of a chemical product, including its design, manufacture, use, and ultimate disposal" [13].

There are many benefits to implementing green chemistry that are inextricably linked to its preventative premise. These include improved economy and business, environment, and human health conditions.

<sup>1</sup> The results have been updated from previously published results (Ranson et al. [16]) to include the 2013 to 2015 TRI data.

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**Figure 3.** Number of source reduction activities.

Pollution can be reduced at its source by a wide variety of techniques, prior to end-of-pipe pollution controls or recycling, such as by changing the product, materials, or processes that generate pollution in the first place. Because of the potential advantages of these preventative approaches, the U.S. EPA took steps to encourage industrial facilities to engage in source reduction. On their part, industrial facilities have engaged in substantial pollution prevention efforts, by carrying out 447,000 unique source reduction activities between 1991 and 2015 (as reported to the EPA's TRI Program).<sup>1</sup> **Figure 2** shows that many facilities (about 107,000) conducted these

Based on the eight source reduction categories tracked, the trend graph above shows that the most reported source reduction category is good operating practices. Source reduction data reported for 2015 (**Figure 3**) show that good operating practices represents 40% followed by the process modifications category at 21%. The two least reported categories are surface

According to the U.S. EPA, "Green chemistry is the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances. Green chemistry applies across the life cycle of a chemical product, including its design, manufacture, use,

There are many benefits to implementing green chemistry that are inextricably linked to its preventative premise. These include improved economy and business, environment, and

The results have been updated from previously published results (Ranson et al. [16]) to include the 2013 to 2015 TRI data.

preparation and finishing as well as cleaning and degreasing.

**3.2. Green chemistry**

and ultimate disposal" [13].

**Figure 2.** Facilities with source reduction projects.

human health conditions.

1

source reduction projects over the past 25 years [12].

156 Green Chemistry

**Economy and business** benefit from reduced waste generation, eliminating costly remediation in the event of accidental releases, hazardous waste disposal, and end-of-the-pipe treatments. Implementing green chemistry saves money by offsetting the costs associated with managing toxic or hazardous chemical waste. In terms of the chemicals, it reduces the need and demand for the manufacture of TRI-listed chemicals while incentivizing the creation of less toxic or non-toxic chemicals, improving competitiveness of chemical manufacturers and their customers. Use of green chemistry and associated safer-product labeling (e.g. Safer Choice labeling) [14] may also lead to increased consumer sales (by earnings).

**The environment** benefits from reduced emissions of TRI-listed chemicals or other hazardous substances, signifying less chemical disruptions to ecosystems. Through green chemistry, the environment would benefit from reductions in emissions of toxics to air, water, and land such as reduced use of landfills, especially hazardous waste landfills. Plants and animals also suffer less harm from reductions in hazardous chemicals entering the environment.

**Human health** also benefits from cleaner environmental conditions. Cleaner air resulting from reductions in hazardous chemicals released to air leads to reduced respiratory disease and other illnesses. Similarly, cleaner water resulting from reductions in hazardous chemicals released to water lead to cleaner drinking and recreational water. Application of green chemistry results in safer consumer products that enter the market and are available for purchase, thereby increasing the safety of consumers and society in general. These products may be new, replacements for less safe products (e.g., certain pesticides, cleaning products), or designed to be manufactured efficiently and with less accompanying waste (e.g., drugs). This preventive practice also benefits the workers in the chemical industry resulting in increased safety through less use of toxic materials, reduced potential for exposure and accidents (e.g., fires or explosions), and reduced need for personal protective equipment.

Given these benefits, it is not surprising to see industry advances in green chemistry. In 2012, the TRI program added six green chemistry source reduction codes to better track these ongoing activities and their possible improvements. These codes are captured within 4 of the 8 categories and are listed in (**Table 4**) along with guidance provided to reporters for increased data quality [15].


*3.2.2. Tracking green chemistry by industry sector*

27% All Others

> Transportation Equipment 9%

**Figure 5.** Green chemistry versus total source reduction by sector, 2012–2015.

Primary Metal 5%

Plastics and Rubber Products 6%

Computer and Electronic Product 6%

0

**Figure 4.** Green chemistry by year and code.

20

2

0

2

0

2

015

202

12

0

2

0

2

015

202

12

0

2

0

2

015

202

12

0

2

0

2

015

202

33% All Others

Plastics and

Rubber Products

Merchant Wholesalers,

> Nondurable Goods 6%

> > Transportation Equipment 7%

6%

12

0

14

13

14

13

14

13

14

13

12

50

100

Number of Activities

150

200

W15

W43

250

On an industry sector level, implementation of green chemistry and total source reduction activities reported from 2012 to 2015 is visible for the top six sectors shown in **Figure 5**. The chemical manufacturing industry makes up the greatest percentage of all green chemistry reporting and constitutes a greater percentage of green chemistry reporting than of total source reduction reporting for the sector (35% vs. 29%). Both metrics are consistent with Fabricated Metal Product Manufacturing in second place, respectively at 13 and 12%. Differences in industry reporting are notable at the third level and beyond with the following observations:

Chemical 34%

Fabricated 13% Metal Product

W50

W56

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W57

2

0

2

015

202

12

0

2

0

2

015

29% Chemical

Primary Metal 7%

Fabricated Metal Product 12%

14

13

14

13

W84

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• The Primary Metal Manufacturing dropping from 7% for all source reduction activities to nearly 5% for only green chemistry. A possible reason for this may be that the nature of the business may not be as amenable to green chemistry as it is in the chemical manufacturing industries. • The Transportation Equipment Manufacturing sector covers the Automotive Manufacturing sector (NAICS 3361-3363) and as expected given recent advances, the majority (70%) of green chemistry reporting is from the auto sector. Overall, the transportation sector represents a larger share of green chemistry reporting compared to total source reduction reporting (9% vs. 7%).

**Green Chemistry All Source Reduction**

**Table 4.** Green chemistry codes and reporting guidance.

#### *3.2.1. Tracking green chemistry by year and code*

From 2012 to 2015, TRI reporting rates by year and code show that of the 37,117 total source reduction activities reported, 1756 (5.1%) were reported as green chemistry (i.e., reported on a Form R using one of the six green chemistry codes). The vast majority were reported as W15 or W50 as shown in **Figure 4**. These relatively high reporting rates indicate that facilities are seizing opportunities for increased monitoring and efficiencies. Whereas a minimum number of facilities reported W57, demonstrating limited implementation of biotechnology in manufacturing processes.

**Figure 4.** Green chemistry by year and code.

Given these benefits, it is not surprising to see industry advances in green chemistry. In 2012, the TRI program added six green chemistry source reduction codes to better track these ongoing activities and their possible improvements. These codes are captured within 4 of the 8 categories and are listed in (**Table 4**) along with guidance provided to reporters for increased data quality [15].

**Green chemistry codes Guidance in TRI reporting forms**

Select code W15 if the introduction of such a system led to a reduction in the amount of the EPCRA Section 313

Select code W43 if the EPCRA Section 313 chemical was a feedstock or reagent chemical and you replaced it (in

• For raw material substitutions not at the level of the individual chemical (e.g., the substitution of natural gas for coal), select instead W42 *Substituted raw materials*. • If use of a feedstock or reagent chemical was reduced or eliminated because of a change in the final product, select instead one of the codes listed under

Select code W50 if the amount of the EPCRA Section 313 chemical generated as waste was reduced by increasing the overall efficiency of the synthesis. • If efficiency of syntheses was improved by using of a different catalyst, select instead W53 Used a different

Select code W56 if the EPCRA Section 313 chemical was used as a solvent in the process and the process was modified such that the EPCRA Section 313 chemical was either replaced or no longer used in as large a quantity. Select code W57 if the use of biotechnology in the process reduced or eliminated the use of the TRI chemical.

Select code W84 if the EPCRA Section 313 chemical had been produced at the facility but was replaced it (in whole or in part) with the production of a different

whole or in part) with a different chemical.

chemical generated as waste.

*Product Modifications*.

process catalyst.

chemical or chemicals.

**W15:** Introduced in-line product quality monitoring or other process analysis system

**W43:** Substituted a feedstock or reagent chemical with a different chemical

conditions or otherwise increased efficiency of synthesis **W56:** Reduced or eliminated use of an organic solvent **W57:** Used biotechnology in manufacturing process

**W84:** Developed a new chemical product to replace a previous chemical product

From 2012 to 2015, TRI reporting rates by year and code show that of the 37,117 total source reduction activities reported, 1756 (5.1%) were reported as green chemistry (i.e., reported on a Form R using one of the six green chemistry codes). The vast majority were reported as W15 or W50 as shown in **Figure 4**. These relatively high reporting rates indicate that facilities are seizing opportunities for increased monitoring and efficiencies. Whereas a minimum number of facilities reported W57, demonstrating limited implementation of biotechnology in manu-

*3.2.1. Tracking green chemistry by year and code*

**Table 4.** Green chemistry codes and reporting guidance.

**Process modifications W50:** Optimized reaction

facturing processes.

**Source reduction categories**

158 Green Chemistry

**Good operating practices**

**Raw material modifications**

**Production modifications**

#### *3.2.2. Tracking green chemistry by industry sector*

On an industry sector level, implementation of green chemistry and total source reduction activities reported from 2012 to 2015 is visible for the top six sectors shown in **Figure 5**. The chemical manufacturing industry makes up the greatest percentage of all green chemistry reporting and constitutes a greater percentage of green chemistry reporting than of total source reduction reporting for the sector (35% vs. 29%). Both metrics are consistent with Fabricated Metal Product Manufacturing in second place, respectively at 13 and 12%. Differences in industry reporting are notable at the third level and beyond with the following observations:

**Figure 5.** Green chemistry versus total source reduction by sector, 2012–2015.


• The Merchants and Wholesalers sector, while actively implementing source reduction activities and within the top six, is almost nil for ranking based on green chemistry with 0.2% representing three activities during the 4-year time period.

Case Study Focus: The study examined TRI data submitted for reporting years 2002 through 2011 and, hence did not include consideration of the green chemistry codes since the codes were implemented for reporting year 2012. Nonetheless, the analyses show that over the 2002–2011 timeframe the quantities of TRI chemicals reported annually by pharmaceutical manufacturing facilities to EPA's TRI Program as released to the environment or otherwise managed as waste declined steadily and by more than 60%. The downward trend was largely driven by reductions in the quantities reported for organic solvents. Five solvents (methanol, dichloromethane, toluene, dimethylformamide and acetonitrile) accounted for three-quarters of the declining trend in production-related waste managed, which includes environmental releases. Overall, the reductions in reported quantities are sector-wide, and it appears that factors such as outsourcing, production levels, regulations, shifts to other waste management practices, or larger pharmaceutical firms did not precipitate the decline. The authors concluded from their analyses and the extensive evidence in the literature of green chemistry advances within the pharma sector that implementation of green chemistry practices is a

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Green chemistry implementation can also be tracked on a chemical level. Industrial facilities reported green chemistry activities to reduce the generation of waste of the following chemicals. **Figure 7** shows the top 8 chemicals based on total green chemistry reporting from 2012 to 2015 and delineates the individual green chemistry codes selected. The majority of green chemistry codes were reported for methanol, toluene, copper, and ammonia, representing 21%. With the chemical manufacturing industry ranking first and the published solvent reduction advancements, TRI data confirm industries' efforts to implement projects to reduce methanol and toluene, the top two most reported chemicals [10]. The top W-codes selected were W50, optimized reaction conditions, followed by W15, in-line product quality monitoring.

0 20 40 60 80 100 120

Used (W57) biotechnology Developed new chemical product (W84)

Reduced an organic solvent (W56)

Optimized reaction (W50) conditions

major contributing factor to the large reductions [10].

Methanol Toluene Copper Ammonia Nickel

Lead Compounds

Nitrate Compounds

In-line product quality (W15) monitoring

**Figure 7.** Green chemistry by chemical.

Lead

Chemical (W43) Substitution

*3.2.3. Tracking green chemistry by chemical*

• The Computer and Electronic Product Manufacturing sector, while not delineated in the source reduction pie chart, falls in seventh position representing 5% of the "all others" category. This indicates that the computer manufacturing sector implemented a consistent share of green chemistry activities to source reduction activities.

How does reporting of green chemistry implementation compare to all TRI reporting? Tracking the implementation of green chemistry in the context of all TRI reports is important because it provides a lens as to sectors more amenable to green chemistry practices and where collaborative efforts may be more readily established. High TRI reporting rates from sectors that do not report green chemistry practices are likely indicators that such sectors face source reduction obstacles. Barriers are discussed in more detail later in the chapter. The pie charts in **Figure 6** show that three of the six sectors fall within the top ranking for both green chemistry and overall TRI reporting. Other sectors such as Petroleum and Coal Products Manufacturing and Utilities, while high in number of TRI forms submitted to TRI, do not report many source reduction activities or specific green chemistry practices for TRIlisted chemicals.

**Figure 6.** Green chemistry versus TRI reporting by sector, 2012–2015.

More in-depth analysis by NAICS code is recommended to help delineate more precisely green chemistry implementation by facilities within specific subsectors of a given industrial sector and their environmental impact. For example, the case study involving TRI and Pharmaceutical Manufacturers to assess the implementation and effectiveness of green chemistry practices focused on facilities classified in NAICS codes 325411 (Medicinal and Botanical Manufacturing) and 325412 (Pharmaceutical Preparation Manufacturing) [10]. This sector represents 16.5% of the chemical manufacturing sector or about 6% of all industry sectors that reported green chemistry practices to TRI from 2012 to 2015.

Case Study Focus: The study examined TRI data submitted for reporting years 2002 through 2011 and, hence did not include consideration of the green chemistry codes since the codes were implemented for reporting year 2012. Nonetheless, the analyses show that over the 2002–2011 timeframe the quantities of TRI chemicals reported annually by pharmaceutical manufacturing facilities to EPA's TRI Program as released to the environment or otherwise managed as waste declined steadily and by more than 60%. The downward trend was largely driven by reductions in the quantities reported for organic solvents. Five solvents (methanol, dichloromethane, toluene, dimethylformamide and acetonitrile) accounted for three-quarters of the declining trend in production-related waste managed, which includes environmental releases. Overall, the reductions in reported quantities are sector-wide, and it appears that factors such as outsourcing, production levels, regulations, shifts to other waste management practices, or larger pharmaceutical firms did not precipitate the decline. The authors concluded from their analyses and the extensive evidence in the literature of green chemistry advances within the pharma sector that implementation of green chemistry practices is a major contributing factor to the large reductions [10].

#### *3.2.3. Tracking green chemistry by chemical*

• The Merchants and Wholesalers sector, while actively implementing source reduction activities and within the top six, is almost nil for ranking based on green chemistry with 0.2%

• The Computer and Electronic Product Manufacturing sector, while not delineated in the source reduction pie chart, falls in seventh position representing 5% of the "all others" category. This indicates that the computer manufacturing sector implemented a consistent

How does reporting of green chemistry implementation compare to all TRI reporting? Tracking the implementation of green chemistry in the context of all TRI reports is important because it provides a lens as to sectors more amenable to green chemistry practices and where collaborative efforts may be more readily established. High TRI reporting rates from sectors that do not report green chemistry practices are likely indicators that such sectors face source reduction obstacles. Barriers are discussed in more detail later in the chapter. The pie charts in **Figure 6** show that three of the six sectors fall within the top ranking for both green chemistry and overall TRI reporting. Other sectors such as Petroleum and Coal Products Manufacturing and Utilities, while high in number of TRI forms submitted to TRI, do not report many source reduction activities or specific green chemistry practices for TRI-

> 39% All Others

6% Coal Products

Petroleum and

23% Chemical

9%

Primary 8% Metal

Utilities

Nondurable 7%

Fabricated

Merchant Wholesalers, Goods 8%

Metal Product

More in-depth analysis by NAICS code is recommended to help delineate more precisely green chemistry implementation by facilities within specific subsectors of a given industrial sector and their environmental impact. For example, the case study involving TRI and Pharmaceutical Manufacturers to assess the implementation and effectiveness of green chemistry practices focused on facilities classified in NAICS codes 325411 (Medicinal and Botanical Manufacturing) and 325412 (Pharmaceutical Preparation Manufacturing) [10]. This sector represents 16.5% of the chemical manufacturing sector or about 6% of all industry sectors that

**Green Chemistry All TRI**

Chemical 34%

Fabricated 13%

Metal Product

reported green chemistry practices to TRI from 2012 to 2015.

representing three activities during the 4-year time period.

share of green chemistry activities to source reduction activities.

listed chemicals.

160 Green Chemistry

27% All Others

> Transportation Equipment 9%

**Figure 6.** Green chemistry versus TRI reporting by sector, 2012–2015.

Primary Metal 5%

Plastics and Rubber Products 6%

Computer and Electronic Product 6%

Green chemistry implementation can also be tracked on a chemical level. Industrial facilities reported green chemistry activities to reduce the generation of waste of the following chemicals. **Figure 7** shows the top 8 chemicals based on total green chemistry reporting from 2012 to 2015 and delineates the individual green chemistry codes selected. The majority of green chemistry codes were reported for methanol, toluene, copper, and ammonia, representing 21%. With the chemical manufacturing industry ranking first and the published solvent reduction advancements, TRI data confirm industries' efforts to implement projects to reduce methanol and toluene, the top two most reported chemicals [10]. The top W-codes selected were W50, optimized reaction conditions, followed by W15, in-line product quality monitoring.

**Figure 7.** Green chemistry by chemical.

#### **3.3. Assessing impact of industrial green chemistry practices**

In practice, implementing source reduction activities aims to improve environmental performance, and as TRI-listed chemicals are eliminated or reduced in processes, facilities consequently reduce associated costs with managing production-related waste of those chemicals. However, what do the data indicate? Do the data confirm that implementation of green chemistry techniques results in reduced waste management and release quantities?

Based on a previous statistical analysis using the "differences-in-differences" methodology, all implemented source reduction is not equal, meaning all activities do not equally decrease the quantities of chemical waste managed. The study, which considered a wide range of TRI data from 1987 to 2012, shows that there is considerable variation in how the implementation of different source reduction activities affects releases. For example, good operating practices, which is the category corresponding to green chemistry code W15, has only a small effect (roughly −4%). In contrast, source reduction activities focused on raw material modifications, which contains green chemistry code W53, shows a large decrease in releases of −20%. Similarly, product modifications, including W84 shows a −13% decrease. The other green chemistry codes fall under the process modifications category, which has shown moderate decreases of −5% [16]. One can infer from this study that to quantify the effectiveness of source reduction, different green chemistry practices would result in different environmental impacts.

BASF CORP-SAVANNAH OPERATIONS, TRIFID 31404KTLST1800E, NAICS 327992: Ground or Treated Mineral and Earth Manufacturing. Facility reported green chemistry code, W50, for nitrate compounds for 2012. The 3 years following show highest releases for 2014,

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ARKEMA INC CLEAR LAKE, TRIFID 77507DWCHM952BB, NAICS 325110: Petrochemical Manufacturing. Facility reported green chemistry code, W50, for two chemicals: butyl acrylate and n-butyl alcohol for 2012. The years following show the highest treatment quantities of butyl acrylate for 2013 with 3,848,260 pounds, 28% of the total treated waste. For n-butyl alcohol, 1,732,045 pounds were treated during 2014, representing 11% of total treated waste during the

The formula used to calculate the normalized trend is as follows. It is applied to all yearfacility-chemical combinations to obtain a normalized production value for each. Year 2009,

*PIyear x* = *PIyear x* − 1 ∗ *PRyear x* (1)

*PIyear <sup>X</sup>* <sup>=</sup> *Wyear <sup>X</sup>*

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

*PIyear <sup>X</sup>* <sup>−</sup> <sup>1</sup> <sup>∗</sup> *PRyear <sup>X</sup>* <sup>−</sup> 1 (2)

*Wyear X*

with 2,860,000 pounds (55% of total releases) discharged to water.

**Figure 8.** Production normalized waste managed, 2009–2015.

as the first year in the series, is set as the base year equal to 1.

PR = production ratio (provided by facility. relative to previous year.)

year.

P = absolute production

W = absolute waste quantity

General formulas:

**Example 1:**

PNW2009 = W2009

PI<sup>2009</sup> = 1

PI = production index relative to 2009

PNW = production normalized waste quantity

*PNWyear X* = \_\_\_\_\_\_\_\_\_\_\_\_

This study also shows that impacts may be experienced up to 5 years following the implementation of a source reduction project. Conducting a similar type of analysis focused on green chemistry practices, especially now that codes are available to clearly track any associated projects would serve as a good case study to verify the overall results. However, additional data is needed to apply this methodology and conduct a robust statistical analysis to observe the long-term impact of green chemistry practices. Within 3–5 years from the time of this writing, sufficient data will be available to evaluate the effectiveness of those activities implemented from 2012 to 2015. As mentioned previously, tracking the same set of facilities over time will ensure visibility of any impacts associated with green chemistry approaches.

#### *3.3.1. Impact of green chemistry on waste managed quantities*

Analysis of the green chemistry practices implemented during 2012 and the impact these practices had on the quantities of TRI chemical waste managed is presented below. To account for at least one factor that could influence changes in the quantities of chemical waste managed, the analysis normalizes based on reported production values. Considering only those facilities that reported green chemistry codes for 2012 and reported production ratios within the normal range (greater than 0.2 and less than 3) and consistently for all years in the time span, the normalized production-related waste managed trend in **Figure 8** shows 7 years of data with 3 years prior to 2012 and 3 years after 2012. The decrease in waste managed during 2012 indicates that green chemistry actions implemented during that year could have contributed to the observed reduction. Investigation into the release quantities for 2013 and 2014 indicates that two facilities are primarily responsible for increases in releases and treatment.

**Figure 8.** Production normalized waste managed, 2009–2015.

BASF CORP-SAVANNAH OPERATIONS, TRIFID 31404KTLST1800E, NAICS 327992: Ground or Treated Mineral and Earth Manufacturing. Facility reported green chemistry code, W50, for nitrate compounds for 2012. The 3 years following show highest releases for 2014, with 2,860,000 pounds (55% of total releases) discharged to water.

ARKEMA INC CLEAR LAKE, TRIFID 77507DWCHM952BB, NAICS 325110: Petrochemical Manufacturing. Facility reported green chemistry code, W50, for two chemicals: butyl acrylate and n-butyl alcohol for 2012. The years following show the highest treatment quantities of butyl acrylate for 2013 with 3,848,260 pounds, 28% of the total treated waste. For n-butyl alcohol, 1,732,045 pounds were treated during 2014, representing 11% of total treated waste during the year.

The formula used to calculate the normalized trend is as follows. It is applied to all yearfacility-chemical combinations to obtain a normalized production value for each. Year 2009, as the first year in the series, is set as the base year equal to 1.

P = absolute production

**3.3. Assessing impact of industrial green chemistry practices**

quantities?

162 Green Chemistry

treatment.

In practice, implementing source reduction activities aims to improve environmental performance, and as TRI-listed chemicals are eliminated or reduced in processes, facilities consequently reduce associated costs with managing production-related waste of those chemicals. However, what do the data indicate? Do the data confirm that implementation of green chemistry techniques results in reduced waste management and release

Based on a previous statistical analysis using the "differences-in-differences" methodology, all implemented source reduction is not equal, meaning all activities do not equally decrease the quantities of chemical waste managed. The study, which considered a wide range of TRI data from 1987 to 2012, shows that there is considerable variation in how the implementation of different source reduction activities affects releases. For example, good operating practices, which is the category corresponding to green chemistry code W15, has only a small effect (roughly −4%). In contrast, source reduction activities focused on raw material modifications, which contains green chemistry code W53, shows a large decrease in releases of −20%. Similarly, product modifications, including W84 shows a −13% decrease. The other green chemistry codes fall under the process modifications category, which has shown moderate decreases of −5% [16]. One can infer from this study that to quantify the effectiveness of source reduction,

different green chemistry practices would result in different environmental impacts.

*3.3.1. Impact of green chemistry on waste managed quantities*

This study also shows that impacts may be experienced up to 5 years following the implementation of a source reduction project. Conducting a similar type of analysis focused on green chemistry practices, especially now that codes are available to clearly track any associated projects would serve as a good case study to verify the overall results. However, additional data is needed to apply this methodology and conduct a robust statistical analysis to observe the long-term impact of green chemistry practices. Within 3–5 years from the time of this writing, sufficient data will be available to evaluate the effectiveness of those activities implemented from 2012 to 2015. As mentioned previously, tracking the same set of facilities over time will ensure visibility of any impacts associated with green chemistry approaches.

Analysis of the green chemistry practices implemented during 2012 and the impact these practices had on the quantities of TRI chemical waste managed is presented below. To account for at least one factor that could influence changes in the quantities of chemical waste managed, the analysis normalizes based on reported production values. Considering only those facilities that reported green chemistry codes for 2012 and reported production ratios within the normal range (greater than 0.2 and less than 3) and consistently for all years in the time span, the normalized production-related waste managed trend in **Figure 8** shows 7 years of data with 3 years prior to 2012 and 3 years after 2012. The decrease in waste managed during 2012 indicates that green chemistry actions implemented during that year could have contributed to the observed reduction. Investigation into the release quantities for 2013 and 2014 indicates that two facilities are primarily responsible for increases in releases and PR = production ratio (provided by facility. relative to previous year.)

PI = production index relative to 2009

W = absolute waste quantity

PNW = production normalized waste quantity

General formulas:

$$\text{Plyear } \mathbf{x} = \text{Plyear } \mathbf{x} - \mathbf{1} \* \text{PRyear } \mathbf{x} \tag{1}$$

$$\begin{array}{l} \text{Player x} = \text{Player x} - 1 \ast \text{PRyear x} \\\\ \text{PNNWyear X} = \frac{\text{Wyear X}}{\text{Player X}} = \frac{\text{Wyear X}}{\text{Player X} - 1 \ast \text{PRyear X} - 1} \end{array} \tag{2}$$

#### **Example 1:**

PI<sup>2009</sup> = 1 PNW2009 = W2009

#### **Example 2:**

PI2010 = PI2009\*PR2010 = PR2010

*PNW*2010 = *W*2010/*PI*2010 = *W*2010/*PR*2010

#### **Example 3:**

PI2011 = PI2010\*PR2011 = PR2009\*PR2010\*PR2011

*PNW*2011 = *W*2011/*PI*2011 = *W*2011/(*PR* 2010<sup>∗</sup> *PR*2011)

In the realm of pollution prevention data, the best way to explore all available P2 information is through **TRI's Pollution Prevention Search Tool** [18]. A user can easily query for all information reported for a specific year or can further limit to a specific chemical or industry. The results table shows the source reductions codes reported along with any optional text. The P2 text filter box can be adjusted to display all comments. This data can then be downloaded and more easily filtered to show only those facilities that reported green chemistry. The P2 tool is also a great way to explore the data on a facility level or to compare to other industries. For general instructions on how to conduct an industry analysis using the P2 tool, see the How-to Guidance [19]. For downloading a comprehensive set of P2 data per reporting year, the **TRI National Analysis supporting data files** are a good resource. Refer to the file "Additional P2 Data" [20]. A quick link is available from TRI's P2 webpage [4] or can be obtained directly from the National Analysis Download Report tab. The Excel workbook packages the P2 data used for EPA's interpretation of the data for the given year's National Analysis report. It is a well-organized workbook with P2 data presented over several tabs including a dedicated tab on 8.10 entries (source reduction

TRI Pollution Prevention Search Tool Easiest method to explore and access P2 related information by

TRI Customized Search Tool Most robust tool for ad-hoc querying of all TRI reported data fields

year

facility and conduct comparisons on an industry scale

The Utility of the Toxic Release Inventory (TRI) in Tracking Implementation and Environmental…

Pre-formatted downloadable P2 data file for a specific reporting

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165

**TRI data resources Description**

**Table 5.** TRI data resources to access green chemistry data.

TRI National Analysis Supporting Data File

"Additional P2 Data" Download

codes reported). These codes can be filtered to those specific to green chemistry.

alternatives to the manufacture, processing, or use of TRI-listed chemicals.

other tables.

**5. Conclusion**

The most robust option to download all possible data fields associated with all facilities that reported green chemistry is **TRI's Customized Search Tool** [21]. This tool provides access to all publicly available TRI reported fields and can be tailored to your data needs. The most comprehensive table is the "flat" view (v\_tri\_form\_r\_ez) and can be selected along with

This chapter describes the utility of the TRI as a useful tool for measuring the impact of green chemistry practices on reducing releases and other waste management quantities of chemicals reportable to the TRI Program, and assessing progress toward sustainability goals. As discussed, the TRI is uniquely well-suited for assessing the progress made by specific industry sectors or specific facilities therein in implementing green chemistry practices. Green chemistry codes as a new data field will become richer with time allowing for more comprehensive analysis of impact. Three to four more years of data will be especially valuable for trend analysis and longer-term assessment of effectiveness. The TRI will continue to be an excellent source for gauging progress toward sustainability as well as for promoting possible

A more direct analysis of the data without consideration of production indicates implementation of green chemistry practices as favorable to lowering waste management quantities. Comparing the 2012 subset of facilities that reported green chemistry codes to all other facilities that reported to the TRI Program for the same year, shows that facilities reporting green chemistry have a larger decrease in their waste managed compared to all facilities. Out of 249 facilities that reported implementation of a green chemistry practice during 2012, 59.2% of those facilities decreased their waste from 2011 to 2015. While 47.6% of facilities that did not report implementation of a green chemistry practice during 2012 decreased their waste from 2011 to 2015.

Assessing impact is both a beneficial exercise and a difficult one because facilities do not directly report the extent to which green chemistry impacts production-related waste managed. However, the optional text that facilities may include in their reports does provide additional insight as to the specific practices implemented and their success. As an example, Cathay Industries USA Inc., in Valparaiso, Indiana in the Chemicals Manufacturing sector, Synthetic Dye and Pigment Manufacturing (NAICS 325130), reported green chemistry code, W50, "Optimized reaction conditions or otherwise increased efficiency of synthesis" for both 2012 and 2013 for ammonia. Normalized production waste management trends of ammonia show decreases in those years, and continued low levels in 2014–2015. Additionally, Cathay Industries noted "Improved measurement and control of reactant / reaction" in the source reduction optional text field for the Form R filed for reporting year 2013 [17]. This additional context could be useful for encouraging similar best practices at other facilities.

More focused analysis by industry sector or green chemistry code would provide more insightful findings as well as more accurate estimates of impact. Analysis of waste managed quantities help to track the overall performance of the facility and more granular analysis of each of the waste management methods, particularly the releases portion, which would inform on progress toward reducing the emission of toxic chemicals to environmental media.

#### **4. Accessing TRI green chemistry data**

Over the time span of the TRI program various tools for accessing and analyzing TRI data have been developed comprising the TRI tool suite available today. Depending on data user objectives, some tools are better suited for certain purposes than others. Three resources are described below and summarized in **Table 5**.


**Table 5.** TRI data resources to access green chemistry data.

**Example 2:**

164 Green Chemistry

**Example 3:**

PI2010 = PI2009\*PR2010 = PR2010

PI2011 = PI2010\*PR2011 = PR2009\*PR2010\*PR2011

similar best practices at other facilities.

**4. Accessing TRI green chemistry data**

described below and summarized in **Table 5**.

*PNW*2010 = *W*2010/*PI*2010 = *W*2010/*PR*2010

*PNW*2011 = *W*2011/*PI*2011 = *W*2011/(*PR* 2010<sup>∗</sup> *PR*2011)

A more direct analysis of the data without consideration of production indicates implementation of green chemistry practices as favorable to lowering waste management quantities. Comparing the 2012 subset of facilities that reported green chemistry codes to all other facilities that reported to the TRI Program for the same year, shows that facilities reporting green chemistry have a larger decrease in their waste managed compared to all facilities. Out of 249 facilities that reported implementation of a green chemistry practice during 2012, 59.2% of those facilities decreased their waste from 2011 to 2015. While 47.6% of facilities that did not report implementation of a green chemistry practice during 2012 decreased their waste from 2011 to 2015.

Assessing impact is both a beneficial exercise and a difficult one because facilities do not directly report the extent to which green chemistry impacts production-related waste managed. However, the optional text that facilities may include in their reports does provide additional insight as to the specific practices implemented and their success. As an example, Cathay Industries USA Inc., in Valparaiso, Indiana in the Chemicals Manufacturing sector, Synthetic Dye and Pigment Manufacturing (NAICS 325130), reported green chemistry code, W50, "Optimized reaction conditions or otherwise increased efficiency of synthesis" for both 2012 and 2013 for ammonia. Normalized production waste management trends of ammonia show decreases in those years, and continued low levels in 2014–2015. Additionally, Cathay Industries noted "Improved measurement and control of reactant / reaction" in the source reduction optional text field for the Form R filed for reporting year 2013 [17]. This additional context could be useful for encouraging

More focused analysis by industry sector or green chemistry code would provide more insightful findings as well as more accurate estimates of impact. Analysis of waste managed quantities help to track the overall performance of the facility and more granular analysis of each of the waste management methods, particularly the releases portion, which would inform on progress toward reducing the emission of toxic chemicals to environmental media.

Over the time span of the TRI program various tools for accessing and analyzing TRI data have been developed comprising the TRI tool suite available today. Depending on data user objectives, some tools are better suited for certain purposes than others. Three resources are In the realm of pollution prevention data, the best way to explore all available P2 information is through **TRI's Pollution Prevention Search Tool** [18]. A user can easily query for all information reported for a specific year or can further limit to a specific chemical or industry. The results table shows the source reductions codes reported along with any optional text. The P2 text filter box can be adjusted to display all comments. This data can then be downloaded and more easily filtered to show only those facilities that reported green chemistry. The P2 tool is also a great way to explore the data on a facility level or to compare to other industries. For general instructions on how to conduct an industry analysis using the P2 tool, see the How-to Guidance [19].

For downloading a comprehensive set of P2 data per reporting year, the **TRI National Analysis supporting data files** are a good resource. Refer to the file "Additional P2 Data" [20]. A quick link is available from TRI's P2 webpage [4] or can be obtained directly from the National Analysis Download Report tab. The Excel workbook packages the P2 data used for EPA's interpretation of the data for the given year's National Analysis report. It is a well-organized workbook with P2 data presented over several tabs including a dedicated tab on 8.10 entries (source reduction codes reported). These codes can be filtered to those specific to green chemistry.

The most robust option to download all possible data fields associated with all facilities that reported green chemistry is **TRI's Customized Search Tool** [21]. This tool provides access to all publicly available TRI reported fields and can be tailored to your data needs. The most comprehensive table is the "flat" view (v\_tri\_form\_r\_ez) and can be selected along with other tables.

#### **5. Conclusion**

This chapter describes the utility of the TRI as a useful tool for measuring the impact of green chemistry practices on reducing releases and other waste management quantities of chemicals reportable to the TRI Program, and assessing progress toward sustainability goals. As discussed, the TRI is uniquely well-suited for assessing the progress made by specific industry sectors or specific facilities therein in implementing green chemistry practices. Green chemistry codes as a new data field will become richer with time allowing for more comprehensive analysis of impact. Three to four more years of data will be especially valuable for trend analysis and longer-term assessment of effectiveness. The TRI will continue to be an excellent source for gauging progress toward sustainability as well as for promoting possible alternatives to the manufacture, processing, or use of TRI-listed chemicals.

## **Disclaimer**

This chapter was prepared by Sandra D. Gaona of the United States Environmental Protection Agency. The contents of this chapter do not necessarily reflect the views, rules or policies of the United States Environmental Protection Agency, nor does mention of any chemical substance necessarily constitute Agency endorsement or recommendation for use. In addition, mention of any companies does not necessarily constitute Agency endorsement.

[9] U.S. Environmental Protection Agency. Toxics Release Inventory (TRI) National Analysis [Internet]. January 2017. https://www.epa.gov/trinationalanalysis. 2015 TRI National

The Utility of the Toxic Release Inventory (TRI) in Tracking Implementation and Environmental…

http://dx.doi.org/10.5772/intechopen.70716

167

[10] DeVito SC, Keenan C, Lazarus D. Can pollutant release and transfer registers (PRTRs) be used to assess implementation and effectiveness of green chemistry practices? A case study involving the Toxics Release Inventory (TRI) and pharmaceutical manufacturers.

[11] U.S. Environmental Protection Agency. Factors to Consider When Using TRI Data [Internet]. 2015. Available from: https://www.epa.gov/sites/production/files/2015-06/

[12] U.S. Environmental Protection Agency. Toxics Release Inventory- 2015 National Analysis Dataset. Retrieved February 2017 from: https://www.epa.gov/toxics-release-inventory-

[13] U.S. Environmental Protection Agency. Basics of Green Chemistry [Internet]. https://www.

[14] U.S. Environmental Protection Agency. Safer Choice. Learn about the Safer Choice Label [Internet]. Available from: https://www.epa.gov/saferchoice/learn-about-safer-choice-label

[15] U.S. Environmental Protection Agency. Toxics Release Inventory Reporting Forms and Instructions. Revised 2015 Version. December 2015. EPA 260-R-15-001. Available from: https://www.epa.gov/sites/production/files/2016-01/documents/ry\_2015\_tri\_reporting\_

[16] Ranson M, Cox B, Keenan C, Teitelbaum D. The impact of pollution prevention on toxic environmental releases from U.S. manufacturing facilities. Environmental Science &

[17] U.S. Environmental Protection Agency. Envirofacts. TRI Pollution Prevention (P2) Search Tool. Cathay Industries Inc.; Ammonia profile. Available from: https://oaspub.epa.gov/ enviro/P2\_EF\_Query.p2\_report?FacilityId=46383PFZRP4901E&ChemicalId=007664417

[18] U.S. Environmental Protection Agency. Envirofacts. TRI Pollution Prevention (P2) Search

[19] U.S. Environmental Protection Agency. TRI Pollution Prevention Resources [Internet]. Available from: https://www.epa.gov/toxics-release-inventory-tri-program/tri-pollution-

[20] U.S. Environmental Protection Agency. TRI National Analysis. Supporting Data Files for the 2015 National Analysis [Internet]. Available from: https://www.epa.gov/trinationalanalysis/

[21] U.S. Environmental Protection Agency. Envirofacts. TRI Customized Search Tool. Available from: https://www.epa.gov/enviro/tri-customized-searchTRIcustomized

Tool. Available from: https://www3.epa.gov/enviro/facts/tri/p2.html

Analysis

Green Chemistry. 2015;**17**:2679-2692

tri-program/download-trinet

forms\_and\_instructions.pdf

prevention-p2-resources

Technology. 2015;**49**(21):12951-12957

&ReportingYear=2014&DocCtrlNum=&Opt=0

supporting-data-files-2015-tri-national-analysis

documents/factors\_to\_consider\_6.15.15\_final.pdf

epa.gov/greenchemistry/basics-green-chemistry#definition

#### **Author details**

Sandra Duque Gaona

Address all correspondence to: gaona.sandra@epa.gov

United States Environmental Protection Agency, Washington, DC, USA

#### **References**


[9] U.S. Environmental Protection Agency. Toxics Release Inventory (TRI) National Analysis [Internet]. January 2017. https://www.epa.gov/trinationalanalysis. 2015 TRI National Analysis

**Disclaimer**

166 Green Chemistry

**Author details**

**References**

Sandra Duque Gaona

listed-chemicals

chap133.pdf

basics-tri-reporting

This chapter was prepared by Sandra D. Gaona of the United States Environmental Protection Agency. The contents of this chapter do not necessarily reflect the views, rules or policies of the United States Environmental Protection Agency, nor does mention of any chemical substance necessarily constitute Agency endorsement or recommendation for use. In addition,

[1] United States Code Title 42. §11001 et seq. Emergency Planning and Community Rightto-Know [Internet]. 1986. Available from: https://www.gpo.gov/fdsys/pkg/USCODE-

[2] U.S. Environmental Protection Agency. Toxics Release Inventory Program. TRI-Listed Chemicals [Internet]. https://www.epa.gov/toxics-release-inventory-tri-program/tri-

[3] United States Code Title 42. §13101 et seq. Pollution Prevention [Internet]. 1990. Available from: https://www.gpo.gov/fdsys/pkg/USCODE-1999-title42/pdf/USCODE-1999-title42-

[4] U.S. Environmental Protection Agency. Toxics Release Inventory Program. Pollution Prevention (P2) and TRI [Internet]. https://www.epa.gov/toxics-release-inventory-tri-

[5] U.S. Environmental Protection Agency. Toxic Chemical Release Inventory Reporting

[6] U.S. Environmental Protection Agency. Toxic Chemical Release Inventory Reporting Form R and Instructions. Revised 1991 Version. [May 1992] EPA 700-K-92-002

[7] U.S. Environmental Protection Agency. Toxics Release Inventory Reporting Forms and Instructions. Revised 2012 Version. February 2013. EPA 260-R-13-001. Available from:

[8] U.S. Environmental Protection Agency. Toxics Release Inventory (TRI) Program. Basics of TRI Reporting [Internet]. https://www.epa.gov/toxics-release-inventory-tri-program/

https://www.epa.gov/sites/production/files/documents/ry2012rfi.pdf

mention of any companies does not necessarily constitute Agency endorsement.

United States Environmental Protection Agency, Washington, DC, USA

2011-title42/html/USCODE-2011-title42-chap116.htm, 2011 Edition

Address all correspondence to: gaona.sandra@epa.gov

program/pollution-prevention-p2-and-tri

Package for 1990. [January 1991] EPA 560/4-91-001


**Section 6**

**Green Approach in Click Chemistry**

**Green Approach in Click Chemistry**

**Chapter 9**

**Provisional chapter**

**Green Approach in Click Chemistry**

**Green Approach in Click Chemistry**

DOI: 10.5772/intechopen.72928

The aim of the topic on click chemistry is used to synthesize various derivatives of 1, 2, 3-triazol-1-yl piperazine, 1, 2, 3-triazol-1-yl quinoxaline, one pot 1,2,3-triazole and bistriazole. These various synthesized compounds were biologically active such as antimicrobial, anti-oxidant, anticancer, antiviral, anti HIV and antitubercular activates. The heterocyclic compounds which are pharmacological active were synthesized by the Cu (I)-catalyzed Huisgen 1, 3-dipolar cycloaddition is a major example based on the click chemistry philosophy. The click chemistry in a broad sense is about using easier reactions to make compounds for certain functions of drugs. The click chemistry used as a green synthesis, because it allows the basic principles of green chemistry given by Anastas and Warner.

**Keywords:** click reaction, sodium ascorbate, cupper sulphate, water, room temperature

In 2001, a Nobel Prize winner K. Barry Sharpless published a landmark review describing a new strategy for organic chemistry [1]. Click reaction advantages of that are high yielding, wide in scope, create only inoffensive byproducts that can be removed without chromatography, are stereo specific, simple to perform, and can be conducted in easily removable or

The environmentally amiable route to carbon-hetero atom bond formation, described as a click chemistry, has become known as a fast, modular, wide in scope, efficient, reliable, simple to perform to the synthesis of novel compounds with desired functionalities [2]. The name "Click Chemistry" was coined to describe this guiding principle – a principle born to meet the demands of modern day chemistry. Among the listed click reactions, Huisgen 1, 3-dipolar cycloaddition between an azide and alkyne have been widely explored due to, among others,

Sachin P. Shirame and Raghunath B. Bhosale

Additional information is available at the end of the chapter

Sachin P. Shirame and Raghunath B. Bhosale

Additional information is available at the end of the chapter

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

© 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

its efficiency, versatility and inertness toward other functional groups.

http://dx.doi.org/10.5772/intechopen.72928

**Abstract**

**1. Introduction**

benign solvents.

**Provisional chapter**

## **Green Approach in Click Chemistry**

**Green Approach in Click Chemistry**

Sachin P. Shirame and Raghunath B. Bhosale Sachin P. Shirame and Raghunath B. Bhosale Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72928

#### **Abstract**

The aim of the topic on click chemistry is used to synthesize various derivatives of 1, 2, 3-triazol-1-yl piperazine, 1, 2, 3-triazol-1-yl quinoxaline, one pot 1,2,3-triazole and bistriazole. These various synthesized compounds were biologically active such as antimicrobial, anti-oxidant, anticancer, antiviral, anti HIV and antitubercular activates. The heterocyclic compounds which are pharmacological active were synthesized by the Cu (I)-catalyzed Huisgen 1, 3-dipolar cycloaddition is a major example based on the click chemistry philosophy. The click chemistry in a broad sense is about using easier reactions to make compounds for certain functions of drugs. The click chemistry used as a green synthesis, because it allows the basic principles of green chemistry given by Anastas and Warner.

DOI: 10.5772/intechopen.72928

**Keywords:** click reaction, sodium ascorbate, cupper sulphate, water, room temperature

**1. Introduction**

In 2001, a Nobel Prize winner K. Barry Sharpless published a landmark review describing a new strategy for organic chemistry [1]. Click reaction advantages of that are high yielding, wide in scope, create only inoffensive byproducts that can be removed without chromatography, are stereo specific, simple to perform, and can be conducted in easily removable or benign solvents.

The environmentally amiable route to carbon-hetero atom bond formation, described as a click chemistry, has become known as a fast, modular, wide in scope, efficient, reliable, simple to perform to the synthesis of novel compounds with desired functionalities [2]. The name "Click Chemistry" was coined to describe this guiding principle – a principle born to meet the demands of modern day chemistry. Among the listed click reactions, Huisgen 1, 3-dipolar cycloaddition between an azide and alkyne have been widely explored due to, among others, its efficiency, versatility and inertness toward other functional groups.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**1.4. Significance of Cu (I)-catalyzed for azide-alkyne cycloaddition reaction**

**1.5. Synthesis of 1, 5-disubstututed 1, 2, 3-triazoles without copper catalyst**

2, 3-triazole are not stable, so we have selected 1, 4-disubstituted 1, 2, 3-triazole.

**Prevention**: Huisgen cycloadditon addition reaction and high yielding.

incorporation of all materials used in the process into the final product.

The cycloaddition was affected by the catalyst RuCl (PPh<sup>3</sup>

thetic route to the requisite triazole.

**Figure 1.** Copper catalyzed azide-alkyne cycloaddition.

**1.6. Click chemistry acts as a green approach**

Chemistry", by Anastas and Warner [9].

desired function while minimizing their toxicity.

**Figure 2.** Ruthenium catalyzed azide alkyne cycloaddition.

Rulf Huisgen 1, 3-dipolar cycloaddition reaction is the copper (I)-catalyzed in which organic azides and terminal alkynes are combined to form 1, 4-regioisomers of 1, 2, 3-triazoles as sole products. This reaction is better termed the Copper (I)-catalyzed Azide-Alkyne Cycloaddition (CuAAC). The Cu (I) species may either be introduced as preformed complexes, or are otherwise generated in the one pot reaction itself by one of the following ways: A copper compound is present in the (+2) oxidation state is added to the reaction in presence of a reducing agent of sodium ascorbate which reduces the Cu from the (+2) oxidation state transfer to the (+1) oxidation state.

There are reported that the formation of regioselective 1, 5-disubstituted triazoles (as shown in **Figure 2**) being mediated by Torne [7, 8], or stereoelectronic effects, but only under harsh conditions. The chemoselectivity of the 1, 3-dipolar cycloaddition enables a convergent syn-

effective for the cycloaddition of secondary azides. The disadvantages of 1, 5-disubstituted 1,

Click Green chemistry has been in place for long as a scientific term without much advantages until recent times when everything wants or needs to be "green". To be scientific, not fancy here, we have try to connect and compare these two, using the "Principles of Green

**Atom economy**: Click chemistry synthetic methods should be designed to maximize the

**Designing safer chemicals**: Huisgen reaction products should be designed to affect their

), which had been reported to be

Green Approach in Click Chemistry

173

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**Mechanism of the click Chemistry**

Rulf Huisgen reported that copper (I) salts were able to accelerate the rate of reaction. More importantly, at room temperature or at moderate temperature, the copper catalyst directs the formation of only one of them regioisomers, the 1, 4-disubstituted as shown in [3, 4].

#### **1.1. Huisgen 1, 3-dipolar cycloaddition reaction**

Rolf Huisgen, is a German chemist his major achievements was the development of the 1,3-dipolar cycloaddition reaction, also known as the Huisgen cycloaddition or Huisgen reaction. The Huisgen 1, 3-dipolar cycloaddition reaction of organic azides and alkynes, has gained considerable attention in recent years due to the introduction in 2001 of Cu (I)-catalysis by Sharpless, a major improvement in both reaction rate and chemoselectivity of the reaction, as realized by the Meldal and the Sharpless laboratories. The great success of the Cu (I)-catalyzed reaction is a quantitative, very robust, insensitive, general and orthogonal ligation reaction and use for even bio-molecular ligation [5].

#### **1.2. Importance of Huisgen 1, 3-dipolar cycloaddition**

Thermodynamic and kinetically favorable (50 and 26 kcal/mol, respectively), Regiospecific, Chemoselective, 107 rate enhancement over non-catalyzed reaction and triazole stable to oxidation and acid hydrolysis.

One pot reactions are reactions where three or more substrates combine in one step to give a product that contains essential parts of all of them [6]. The idea of using a one pot reactions followed by a Huisgen [3+2] copper catalyzed reaction was first presented by Barbas and coworkers.

#### **1.3. Synthesis of 1, 4-disubstituted 1, 2, 3-triazoles with copper catalyst**

The copper (I)-catalyzed union of terminal alkynes and organic azides to give 1, 4-disubstituted 1, 2, 3-triazoles (as shown in **Figure 1**) exhibits remarkably broad scope and exquisite selectivity. Particularly, 1, 4-disubstituted 1, 2, 3-triazole fragment exhibit is useful for potent biological properties.

**Figure 1.** Copper catalyzed azide-alkyne cycloaddition.

**Mechanism of the click Chemistry**

Rulf Huisgen reported that copper (I) salts were able to accelerate the rate of reaction. More importantly, at room temperature or at moderate temperature, the copper catalyst directs the

Rolf Huisgen, is a German chemist his major achievements was the development of the 1,3-dipolar cycloaddition reaction, also known as the Huisgen cycloaddition or Huisgen reaction. The Huisgen 1, 3-dipolar cycloaddition reaction of organic azides and alkynes, has gained considerable attention in recent years due to the introduction in 2001 of Cu (I)-catalysis by Sharpless, a major improvement in both reaction rate and chemoselectivity of the reaction, as realized by the Meldal and the Sharpless laboratories. The great success of the Cu (I)-catalyzed reaction is a quantitative, very robust, insensitive, general and orthogonal liga-

Thermodynamic and kinetically favorable (50 and 26 kcal/mol, respectively), Regiospecific,

One pot reactions are reactions where three or more substrates combine in one step to give a product that contains essential parts of all of them [6]. The idea of using a one pot reactions followed by a Huisgen [3+2] copper catalyzed reaction was first presented by Barbas and coworkers.

The copper (I)-catalyzed union of terminal alkynes and organic azides to give 1, 4-disubstituted 1, 2, 3-triazoles (as shown in **Figure 1**) exhibits remarkably broad scope and exquisite selectivity. Particularly, 1, 4-disubstituted 1, 2, 3-triazole fragment exhibit is useful for potent

**1.3. Synthesis of 1, 4-disubstituted 1, 2, 3-triazoles with copper catalyst**

rate enhancement over non-catalyzed reaction and triazole stable to oxi-

formation of only one of them regioisomers, the 1, 4-disubstituted as shown in [3, 4].

**1.1. Huisgen 1, 3-dipolar cycloaddition reaction**

tion reaction and use for even bio-molecular ligation [5].

**1.2. Importance of Huisgen 1, 3-dipolar cycloaddition**

Chemoselective, 107

172 Green Chemistry

biological properties.

dation and acid hydrolysis.

#### **1.4. Significance of Cu (I)-catalyzed for azide-alkyne cycloaddition reaction**

Rulf Huisgen 1, 3-dipolar cycloaddition reaction is the copper (I)-catalyzed in which organic azides and terminal alkynes are combined to form 1, 4-regioisomers of 1, 2, 3-triazoles as sole products. This reaction is better termed the Copper (I)-catalyzed Azide-Alkyne Cycloaddition (CuAAC). The Cu (I) species may either be introduced as preformed complexes, or are otherwise generated in the one pot reaction itself by one of the following ways: A copper compound is present in the (+2) oxidation state is added to the reaction in presence of a reducing agent of sodium ascorbate which reduces the Cu from the (+2) oxidation state transfer to the (+1) oxidation state.

#### **1.5. Synthesis of 1, 5-disubstututed 1, 2, 3-triazoles without copper catalyst**

There are reported that the formation of regioselective 1, 5-disubstituted triazoles (as shown in **Figure 2**) being mediated by Torne [7, 8], or stereoelectronic effects, but only under harsh conditions. The chemoselectivity of the 1, 3-dipolar cycloaddition enables a convergent synthetic route to the requisite triazole.

The cycloaddition was affected by the catalyst RuCl (PPh<sup>3</sup> ), which had been reported to be effective for the cycloaddition of secondary azides. The disadvantages of 1, 5-disubstituted 1, 2, 3-triazole are not stable, so we have selected 1, 4-disubstituted 1, 2, 3-triazole.

#### **1.6. Click chemistry acts as a green approach**

Click Green chemistry has been in place for long as a scientific term without much advantages until recent times when everything wants or needs to be "green". To be scientific, not fancy here, we have try to connect and compare these two, using the "Principles of Green Chemistry", by Anastas and Warner [9].

**Prevention**: Huisgen cycloadditon addition reaction and high yielding.

**Atom economy**: Click chemistry synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.

**Designing safer chemicals**: Huisgen reaction products should be designed to affect their desired function while minimizing their toxicity.

**Figure 2.** Ruthenium catalyzed azide alkyne cycloaddition.

**Safer solvents and auxiliaries**: Click chemistry in reaction medium is used water as the solvent.

on nucleophilic substitution reaction in the presence of NaN3

**Reaction conditions**: **(a)** 1-bromo-3-chloropropane, aq.NaOH, acetone RT, 24 h. **(b)** NaN3

O, Copper sulfate, sodium ascorbate, RT, 10–12 h.

**Step (i)**: To the solution of 1-(3-chlorophenyl)-piperazine **(1)** (0.43 mmol) in water (5 mL) was added sodium hydroxide (1.15 mmol) followed by 1-bromo-3-chloropropane (0.911 mmol) under stirring at 25–30°C. The reaction mixture was further stirred for 24 h at same temperature and progress of reaction was monitored by TLC. After completion of the reaction, the reaction mass was extracted with ethyl acetate. The organic layer was separated and dried over sodium sulfate to obtain pale yellow oily product **(2)** after evaporation of ethyl

**Step (ii)**: Sodium azide (6.5 mmol) was added to a solution of 1-(3-chlorophenyl)-4-(3-chloropropyl) piperazine (**2**) (5.0 mmol) in 30 mL DMSO under stirring. The reaction mixture was stirred for 3–4 h at 50–55°C. The reaction progress was monitored by TLC. After completion of reaction, the reaction mixture was poured on crushed ice, which was extracted with ethyl acetate. The organic layer was separated and washed with water and brine solution, dried over sodium sulfate to obtain yellow oily crude product. The crude product was purified by column chromatography (ethyl acetate: n-hexane) to obtain pure yellow oily product (**3**).

3-dipolar cycloaddition reaction.

reaction, R-Substituted alkynes, THF: H2

**2.2. General procedure**

acetate.

azide intermediated 1-(3-azidopropyl)-4-(3-chlorophenyl) piperazine in good to excellent yield. We have prepared the piperazine triazole by the Huisgen 1, 3-dipolar cycloaddition reaction of 1-(3-azidopropyl) 4-(3-chlorophenyl) piperazine with various substituted alkynes which was prepared reported method in the presence of Cu (I)-catalyst and we got very high yield. The continued interest for the development of efficient and environmentally friendly procedures for the synthesis of heterocyclic compounds, used copper sulfate with its easy availability, cheap cost and operational simplicity prompted us to explore the synthesis of 1,

and DMSO at 40–45°C, to afford

http://dx.doi.org/10.5772/intechopen.72928

Green Approach in Click Chemistry

175

, DMSO, 50–55°C, 4–5 h. **(c)** Click

**Design for energy efficiency**: Click chemistry is a lot of reactions can be done without much heating.

**Reduce derivatives**: Click chemistry is a biggest for its superior selectivity and tolerance of most functional groups.

**Catalysis**: Click chemistry is used for chemical or light catalysts.

**Inherently safer chemistry for accident prevention**: The use of azides in 1,3 dipolar cycloaddition reaction are minimize the chemical accident.

Advantages of click chemistry:

	- **IX.** Reaction work-up and product isolation must be simple, without requiring chromatographic purification [10].

#### **1.7. Pharmaceutical applications of Triazoles**

Heterocyclic compounds containing nitrogen plays an important role in agrochemical and pharmaceuticals. The basic heterocyclic rings present in the various medicinal agents are mainly 1, 2, 3-triazole and 1, 2, 4-triazole [11]. Derivatives of 1, 2, 3-triazole have found to anti-HIV, anti-allergenic, antimicrobial, cytostatic, virostatic, anti-inflammatory and antibacterial [12] activities. Triazoles are also being studied for the treatment of obesity and osteoarthritis.

#### **2. Experimental section**

#### **2.1. Synthesis of piperazine using click chemistry**

In the present investigation, the synthesis of 1-(3-azidopropyl)-4-(3-chlorophenyl) piperazine were synthesized from 1-(3-chlorophenyl)-4-(3-chloropropyl) piperazine compound which on nucleophilic substitution reaction in the presence of NaN3 and DMSO at 40–45°C, to afford azide intermediated 1-(3-azidopropyl)-4-(3-chlorophenyl) piperazine in good to excellent yield. We have prepared the piperazine triazole by the Huisgen 1, 3-dipolar cycloaddition reaction of 1-(3-azidopropyl) 4-(3-chlorophenyl) piperazine with various substituted alkynes which was prepared reported method in the presence of Cu (I)-catalyst and we got very high yield. The continued interest for the development of efficient and environmentally friendly procedures for the synthesis of heterocyclic compounds, used copper sulfate with its easy availability, cheap cost and operational simplicity prompted us to explore the synthesis of 1, 3-dipolar cycloaddition reaction.

**Reaction conditions**: **(a)** 1-bromo-3-chloropropane, aq.NaOH, acetone RT, 24 h. **(b)** NaN3 , DMSO, 50–55°C, 4–5 h. **(c)** Click reaction, R-Substituted alkynes, THF: H2 O, Copper sulfate, sodium ascorbate, RT, 10–12 h.

#### **2.2. General procedure**

**Safer solvents and auxiliaries**: Click chemistry in reaction medium is used water as the solvent. **Design for energy efficiency**: Click chemistry is a lot of reactions can be done without much

**Reduce derivatives**: Click chemistry is a biggest for its superior selectivity and tolerance of

**Inherently safer chemistry for accident prevention**: The use of azides in 1,3 dipolar cycload-

**VII.** Click reaction must be of wide scope, giving consistently high yields with a variety of

**VIII.** It must be easy to perform, be insensitive to oxygen or water and use only readily avail-

**IX.** Reaction work-up and product isolation must be simple, without requiring chromato-

Heterocyclic compounds containing nitrogen plays an important role in agrochemical and pharmaceuticals. The basic heterocyclic rings present in the various medicinal agents are mainly 1, 2, 3-triazole and 1, 2, 4-triazole [11]. Derivatives of 1, 2, 3-triazole have found to anti-HIV, anti-allergenic, antimicrobial, cytostatic, virostatic, anti-inflammatory and antibacterial [12] activities. Triazoles are also being studied for the treatment of obesity and osteoarthritis.

In the present investigation, the synthesis of 1-(3-azidopropyl)-4-(3-chlorophenyl) piperazine were synthesized from 1-(3-chlorophenyl)-4-(3-chloropropyl) piperazine compound which

**Catalysis**: Click chemistry is used for chemical or light catalysts.

**III.** To form a desired product in a simple and quantitative way.

dition reaction are minimize the chemical accident.

**I.** The mixture owns only stable compounds.

**IV.** Energetically highly favorable linking reaction.

**V.** The purification can be done on large scale.

heating.

174 Green Chemistry

most functional groups.

Advantages of click chemistry:

**II.** The reaction owns a high yield.

**VI.** The linkage is chemoselective.

graphic purification [10].

**1.7. Pharmaceutical applications of Triazoles**

**2.1. Synthesis of piperazine using click chemistry**

starting materials.

able reagents.

**2. Experimental section**

**Step (i)**: To the solution of 1-(3-chlorophenyl)-piperazine **(1)** (0.43 mmol) in water (5 mL) was added sodium hydroxide (1.15 mmol) followed by 1-bromo-3-chloropropane (0.911 mmol) under stirring at 25–30°C. The reaction mixture was further stirred for 24 h at same temperature and progress of reaction was monitored by TLC. After completion of the reaction, the reaction mass was extracted with ethyl acetate. The organic layer was separated and dried over sodium sulfate to obtain pale yellow oily product **(2)** after evaporation of ethyl acetate.

**Step (ii)**: Sodium azide (6.5 mmol) was added to a solution of 1-(3-chlorophenyl)-4-(3-chloropropyl) piperazine (**2**) (5.0 mmol) in 30 mL DMSO under stirring. The reaction mixture was stirred for 3–4 h at 50–55°C. The reaction progress was monitored by TLC. After completion of reaction, the reaction mixture was poured on crushed ice, which was extracted with ethyl acetate. The organic layer was separated and washed with water and brine solution, dried over sodium sulfate to obtain yellow oily crude product. The crude product was purified by column chromatography (ethyl acetate: n-hexane) to obtain pure yellow oily product (**3**).

**Step (iii)**: The azide compound **(3)** (1.0 mmol) and alkyne (1.1 mmol) were dissolved in THF/ H2 O (1:1), CuSO4 ·5H2 O (0.05 mmol) and sodium ascorbate (0.40 mmol). The reaction mixture was stirred for 10 h at room temperature. The progress of reaction was monitored by TLC. After completion of reaction, reaction mixture was poured on crushed ice. The solid obtained was extracted with ethyl acetate. The organic extract was washed with water and brine. The solvent was removed under reduced pressure to afford crude product, which was purified from ethanol to obtain pure compounds.

H2 SO4

H2

compounds.

halides, NaN3

**Reagent and conditions: (a)** NaN3

dle azides.

O (9:1). To this solution, CuSO4

 (3 mL) at 0°C over 5 min. The reaction mixture was stirred at 0°C for 30 min. Then added solution of sodium azide (4.40 mmol) in water (5 mL). The solution was allowed to attain room temperature and keep stirring for 5 h. The progress of reaction was monitored by TLC. The reaction mass was precipitated, filtered and washed with water. Brown colored crude product was recrystallized from aqueous methanol to obtain pure azide

**Step (ii)**: The azide compound (1.0 mmol) and alkyne (1.1 mmol) were dissolved in DMF/

added. The reaction mixture was stirred for 11 h at room temperature. The progress of reaction was monitored by TLC. After completion of reaction, reaction mixture was poured on crushed ice. The solid product was extracted with ethyl acetate. The organic extract was washed with water and brine. The solvent was removed under reduced pressure to afford crude product,

The chemoselective azide and alkyne cycloadditions at room temperature in organic medium. K. Barry Sharpless and co-workers have reported a high yielding synthesis of triazoles using a Cu (I)-catalyst with an excellent 1, 4-regioselectivity. The resulting "clicked" products can even be obtained via in situ generation of the corresponding organic azides,

in the presence of an alkyne and a copper catalyst, avoiding the need to han-

O (0.05 mmol) and sodium ascorbate (0.40 mmol) were

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·5H2

which was recrystallized from methanol to obtain pure compound.

, CUI (10%), PEG-400.

**2.5. Synthesis of 1, 2, 3-triazoles by one pot method by using click chemistry**

#### **2.3. Synthesis of quinoxaline by using click chemistry**

In the present investigation, the 6-azido-5-bromo quinoxaline were synthesized from 5-bromo quinoxalin-6-amine compound, which on diazotization in the presence of concentrated sulfuric acid, water and sodium nitrite at temperature 0–5°C which undergoes and nucleophilic substitution reaction with sodium azide to afford the 6-azido-5-bromo quinoxaline in good to excellent yield. The quinoxaline 1, 2, 3 triazole derivatives were prepared by the copper catalyzed azide and alkyne cycloaddition reaction of 6-azido-5-bromoquinoxaline with various substituted alkynes were prepared by reported method using copper sulfate and sodium ascorbate in DMF:H2 O as a reaction medium at room temperature to obtain 1,2,3-triazole quinoxaline as shown scheme. The synthesized products were obtained in good to excellent yields. The progress of the reaction was monitored by TLC. Some synthesized compounds were characterized by IR, 1 H NMR, 13C NMR and Mass spectroscopy methods. Some synthesized compounds are antioxidant, antibacterial and antifungal activities have been evaluated.

**Reaction conditions: (a)** H2 O, H2 SO4 , NaNO2 , NaN3 , 0–5°C to RT, 3 h. **(b)** Click reaction, RTHF: H2 O, Copper sulfate, sodium ascorbate, RT, 10–13 h.

#### **2.4. General procedure**

**Step (i)**: A solution of sodium nitrate (3.13 mmol) in water (8 mL) was added dropwise to a solution of 4-amino-5-bromoquinoxaline **(i)** (2.45 mmol) in water (5 mL) and concentrated H2 SO4 (3 mL) at 0°C over 5 min. The reaction mixture was stirred at 0°C for 30 min. Then added solution of sodium azide (4.40 mmol) in water (5 mL). The solution was allowed to attain room temperature and keep stirring for 5 h. The progress of reaction was monitored by TLC. The reaction mass was precipitated, filtered and washed with water. Brown colored crude product was recrystallized from aqueous methanol to obtain pure azide compounds.

**Step (ii)**: The azide compound (1.0 mmol) and alkyne (1.1 mmol) were dissolved in DMF/ H2 O (9:1). To this solution, CuSO4 ·5H2 O (0.05 mmol) and sodium ascorbate (0.40 mmol) were added. The reaction mixture was stirred for 11 h at room temperature. The progress of reaction was monitored by TLC. After completion of reaction, reaction mixture was poured on crushed ice. The solid product was extracted with ethyl acetate. The organic extract was washed with water and brine. The solvent was removed under reduced pressure to afford crude product, which was recrystallized from methanol to obtain pure compound.

#### **2.5. Synthesis of 1, 2, 3-triazoles by one pot method by using click chemistry**

The chemoselective azide and alkyne cycloadditions at room temperature in organic medium. K. Barry Sharpless and co-workers have reported a high yielding synthesis of triazoles using a Cu (I)-catalyst with an excellent 1, 4-regioselectivity. The resulting "clicked" products can even be obtained via in situ generation of the corresponding organic azides, halides, NaN3 in the presence of an alkyne and a copper catalyst, avoiding the need to handle azides.

**Reagent and conditions: (a)** NaN3 , CUI (10%), PEG-400.

**Step (iii)**: The azide compound **(3)** (1.0 mmol) and alkyne (1.1 mmol) were dissolved in THF/

ture was stirred for 10 h at room temperature. The progress of reaction was monitored by TLC. After completion of reaction, reaction mixture was poured on crushed ice. The solid obtained was extracted with ethyl acetate. The organic extract was washed with water and brine. The solvent was removed under reduced pressure to afford crude product, which was

In the present investigation, the 6-azido-5-bromo quinoxaline were synthesized from 5-bromo quinoxalin-6-amine compound, which on diazotization in the presence of concentrated sulfuric acid, water and sodium nitrite at temperature 0–5°C which undergoes and nucleophilic substitution reaction with sodium azide to afford the 6-azido-5-bromo quinoxaline in good to excellent yield. The quinoxaline 1, 2, 3 triazole derivatives were prepared by the copper catalyzed azide and alkyne cycloaddition reaction of 6-azido-5-bromoquinoxaline with various substituted alkynes were prepared by reported method using copper sulfate and sodium

quinoxaline as shown scheme. The synthesized products were obtained in good to excellent yields. The progress of the reaction was monitored by TLC. Some synthesized compounds

sized compounds are antioxidant, antibacterial and antifungal activities have been evaluated.

O (0.05 mmol) and sodium ascorbate (0.40 mmol). The reaction mix-

O as a reaction medium at room temperature to obtain 1,2,3-triazole

H NMR, 13C NMR and Mass spectroscopy methods. Some synthe-

, 0–5°C to RT, 3 h. **(b)** Click reaction, RTHF: H2

O, Copper sulfate,

H2

176 Green Chemistry

O (1:1), CuSO4

ascorbate in DMF:H2

**Reaction conditions: (a)** H2

sodium ascorbate, RT, 10–13 h.

**2.4. General procedure**

O, H2 SO4

, NaNO2

, NaN3

**Step (i)**: A solution of sodium nitrate (3.13 mmol) in water (8 mL) was added dropwise to a solution of 4-amino-5-bromoquinoxaline **(i)** (2.45 mmol) in water (5 mL) and concentrated

were characterized by IR, 1

·5H2

purified from ethanol to obtain pure compounds.

**2.3. Synthesis of quinoxaline by using click chemistry**

#### **2.6. General procedure**

Substituted halide (1.0 mmol), sodium azide (1.4 mmol) and Substituted alkynes (1.1 mmol) were charged into the single neck R.B. flask contains polyethylene glycol-400 (5 mL). Catalytic amount of copper iodide (10 mol %) were added into the reaction mixture and maintain it for 6 h at 40–45°C. The progress of reaction was monitored by TLC. After completion of reaction, the mixture was poured on crushed ice. The isolated product was extracted with ethyl acetate. The organic layer was separated and washed with water and brine solution. The solvent was removed under reduced pressure and the isolated crude product was recrystallized from ethanol to obtain pure compounds.

and dried by MgSO4

**3. Result and discussion**

several research groups.

**4. Conclusion**

**1**

. The organic solvent was evaporated under reduced pressure to get crude

and DMSO-d6

) stretching

179

showed spectra the

Green Approach in Click Chemistry

http://dx.doi.org/10.5772/intechopen.72928

product. The isolated crude product was recrystallized from ethanol to obtain pure compound.

vibrations. IR spectrums in azido and alkyne peak are disappeared to confirmed 1, 2, 3-triazole formation, of compounds. These assignments are in agreement with those observed by

proton in triazole ring significantly observed in the region at δ 8.62–7.81 ppm and adjacent sp<sup>2</sup> hybridized carbon of that proton at δ 129.68–127.86 ppm in <sup>13</sup>C NMR. These findings are in

The mass spectra of corresponding 1, 2, 3-triazol-1-yl piperazine show their molecular for-

We have successfully introduced azide-alkyne 1, 3-dipolar cycloaddition reaction in heterocyclic chemistry. Due to the presence of triazole it observed that enhancing the bioactivity of basic moieties at different heterocycles. We have concluded that a series of novel 1, 2, 3-triazol-1-yl piperazine, quinoxaline, one pot 1,2,3-triazole and bistriazole derivatives by using click chemistry. These derivatives we have achieved by using Husign 1, 3-dipolar cycloaddition which is green chemistry approach because of high yield, high purity, stereo specific,

I gratefully acknowledge my deep gratitude to the **Prof. N. N. Maldar**, Vice Chancellor, Solapur University and **Prof. R. B. Bhosale** research guide & Director, School of Chemical

Sciences, Solapur University Solapur for providing necessary laboratory facilities.

School of Chemical Sciences, Solapur University, Solapur, Maharashtra State, India

**IR** spectra of azide showed characteristic band at near region 2113 cm−1 due to (–N3

**H NMR** spectra of compounds were studied in CDCl3

agreements with those observed by different workers.

simple to perform, using green solvents.

Sachin P. Shirame\* and Raghunath B. Bhosale

\*Address all correspondence to: sachinshirame@gmail.com

**Acknowledgements**

**Author details**

mula weight and found to be in agreement with the literature.

#### **2.7. Synthesis of 1, 2, 3-bistriazoles by using click chemistry**

Present investigation in the synthesis of 1, 2, 3-bistriazole, the most widely used is the Cu (I)-catalyzed 1, 3 dipolar cycloaddition reaction in which the condensation of a bis-halide with an substituted alkynes were prepared by reported method in the presence of NaN3 , Na2 CO3, CuSO4 ·5H2 O, ascorbic acid, DMF: H2 O, 15–20 h, r.t. We have synthesized the 1, 2, 3-bistriazole derivatives by changing the pharmacophore and changing the position of the pharmacophore on substituted alkynes. These synthesized new drug scaffold. The synthesized compounds were evaluated for antibacterial activity and carcinogenicity study.

**Reagents and condition: (a)** NaN3 , DMSO, 45–50°C, 4–5 h. **(b)** CuI, DIPEA, DMF, 5–6 h, 55–60°C.

#### **2.8. General procedure**

To a stirred solution of 1, 3-dibromopropane (1.5 mmol) in DMF: H2 O (4:1) 15 mL; NaN3 (3.2 mmol), Na2 CO3 (2.2 mmol), CuSO4 ·5H2 O (0.6 mmol), ascorbic acid (2.2 mmol) and phenyl acetylene (3.1 mmol) were added. The reaction mixture was stirred at room temperature for 20 h. The progress of reaction monitored by TLC. Then, aqueous NH4 OH and CH2 Cl2 were added in the reaction mixture and the organic layer was separated and washed with water, brine solution and dried by MgSO4 . The organic solvent was evaporated under reduced pressure to get crude product. The isolated crude product was recrystallized from ethanol to obtain pure compound.

## **3. Result and discussion**

**2.6. General procedure**

178 Green Chemistry

CuSO4

·5H2

**Reagents and condition: (a)** NaN3

CO3

**2.8. General procedure**

(3.2 mmol), Na2

ethanol to obtain pure compounds.

**2.7. Synthesis of 1, 2, 3-bistriazoles by using click chemistry**

were evaluated for antibacterial activity and carcinogenicity study.

To a stirred solution of 1, 3-dibromopropane (1.5 mmol) in DMF: H2

·5H2

acetylene (3.1 mmol) were added. The reaction mixture was stirred at room temperature for 20 h.

the reaction mixture and the organic layer was separated and washed with water, brine solution

(2.2 mmol), CuSO4

The progress of reaction monitored by TLC. Then, aqueous NH4

O, ascorbic acid, DMF: H2

Substituted halide (1.0 mmol), sodium azide (1.4 mmol) and Substituted alkynes (1.1 mmol) were charged into the single neck R.B. flask contains polyethylene glycol-400 (5 mL). Catalytic amount of copper iodide (10 mol %) were added into the reaction mixture and maintain it for 6 h at 40–45°C. The progress of reaction was monitored by TLC. After completion of reaction, the mixture was poured on crushed ice. The isolated product was extracted with ethyl acetate. The organic layer was separated and washed with water and brine solution. The solvent was removed under reduced pressure and the isolated crude product was recrystallized from

Present investigation in the synthesis of 1, 2, 3-bistriazole, the most widely used is the Cu (I)-catalyzed 1, 3 dipolar cycloaddition reaction in which the condensation of a bis-halide with

derivatives by changing the pharmacophore and changing the position of the pharmacophore on substituted alkynes. These synthesized new drug scaffold. The synthesized compounds

, DMSO, 45–50°C, 4–5 h. **(b)** CuI, DIPEA, DMF, 5–6 h, 55–60°C.

O, 15–20 h, r.t. We have synthesized the 1, 2, 3-bistriazole

, Na2 CO3,

O (4:1) 15 mL; NaN3

were added in

Cl2

O (0.6 mmol), ascorbic acid (2.2 mmol) and phenyl

OH and CH2

an substituted alkynes were prepared by reported method in the presence of NaN3

**IR** spectra of azide showed characteristic band at near region 2113 cm−1 due to (–N3 ) stretching vibrations. IR spectrums in azido and alkyne peak are disappeared to confirmed 1, 2, 3-triazole formation, of compounds. These assignments are in agreement with those observed by several research groups.

**1 H NMR** spectra of compounds were studied in CDCl3 and DMSO-d6 showed spectra the proton in triazole ring significantly observed in the region at δ 8.62–7.81 ppm and adjacent sp<sup>2</sup> hybridized carbon of that proton at δ 129.68–127.86 ppm in <sup>13</sup>C NMR. These findings are in agreements with those observed by different workers.

The mass spectra of corresponding 1, 2, 3-triazol-1-yl piperazine show their molecular formula weight and found to be in agreement with the literature.

#### **4. Conclusion**

We have successfully introduced azide-alkyne 1, 3-dipolar cycloaddition reaction in heterocyclic chemistry. Due to the presence of triazole it observed that enhancing the bioactivity of basic moieties at different heterocycles. We have concluded that a series of novel 1, 2, 3-triazol-1-yl piperazine, quinoxaline, one pot 1,2,3-triazole and bistriazole derivatives by using click chemistry. These derivatives we have achieved by using Husign 1, 3-dipolar cycloaddition which is green chemistry approach because of high yield, high purity, stereo specific, simple to perform, using green solvents.

#### **Acknowledgements**

I gratefully acknowledge my deep gratitude to the **Prof. N. N. Maldar**, Vice Chancellor, Solapur University and **Prof. R. B. Bhosale** research guide & Director, School of Chemical Sciences, Solapur University Solapur for providing necessary laboratory facilities.

#### **Author details**

Sachin P. Shirame\* and Raghunath B. Bhosale

\*Address all correspondence to: sachinshirame@gmail.com

School of Chemical Sciences, Solapur University, Solapur, Maharashtra State, India

#### **References**


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