**6**

## **Greener Solvent-Free Reactions on ZnO**

## Mona Hosseini-Sarvari

*Department of Chemistry, Faculty of Science, Shiraz University, Shiraz, I. R. Iran* 

### **1. Introduction**

102 Green Chemistry – Environmentally Benign Approaches

Venzke, D.; Flores, A. F. C.; Quina, F. H.; Pizzuti, L. & Pereira, C. M. P. (2011). Ultrasound

Yuan, Y.-Q. & Guo, S.-R. (2011). TMSCl/Fe(NO3)3-Catalyzed synthesis of 2-

Zang, H.; Su, Q.; Mo, Y.; Cheng, B.-W. & Jun, S. (2010). Ionic liquid [emim]OAc under

Zou, Y.; Wu, H.; Hu, Y.; Liu, H.; Zhao, X.; Ji, H. & Shi, D. (2011). A novel and environment-

ultrasound irradiation. *Ultrasonics Sonochemistry*, Vol. 18, pp. 708-712.

phenylthiazoles. *Ultrasonics Sonochemistry*, Vol. 18, pp. 370-374.

*Communications*, Vol. 41, pp. 2169-2177.

*Ultrasonics Sonochemistry*, Vol. 17, pp. 749-751.

pp. 911-916.

aqueous solution under ultrasound irradiation. *Ultrasonics Sonochemistry*, Vol. 18,

promoted greener synthesis of 2-(3,5-diaryl-4,5-dihydro-1*H*-pyrazol-1-yl)-4-

arylbenzothiazoles and 2-arylbenzimidazoles under ultrasonic irradiation. *Synthetic* 

ultrasonic irradiation towards the first synthesis of trisubstituted imidazoles.

friendly method for preparing dihydropyrano[2,3-*c*]pyrazoles in water under

Due to the growing concern for the influence of the organic solvent on the environment as well as on human body, organic reactions without use of conventional organic solvents have attracted the attention of synthetic organic chemists. Although a number of modern solvents, such as fluorous media, ionic liquids and water have been extensively studied recently, not using a solvent at all is definitely the best option. Development of solvent-free organic reactions is thus gaining prominence.

During the last decades, a central objective in synthetic organic chemistry has been to develop greener and more economically competitive processes for the efficient synthesis of biologically active compounds with potential application in the pharmaceutical or agrochemical industries. In this context, the solventless approach is simple with amazing versatility. It reduces the use of organic solvents and minimizes the formation of other waste. The reactions occur under mild conditions and usually require easier workup procedures and simpler equipment. Moreover, it may allow access to compounds that require harsh reaction conditions under traditional approaches or when the yields are too low to be of practical convenience. Because of economy and pollution, solvent-free reactions are of great interest in order to modernize classical procedures making them more clean, safe and easy to perform. Reactions on solid mineral supports, reactions without any solvent/support or catalyst, and solid-liquid phase transfer catalysis can be thus employed with noticeable increases in reactivity and selectivity. Therefore the following benefits could be mentioned for solvent-free conditions:


Zinc oxide was known for a long time, since it was a by-product of copper smelting. ZnO has been intensively studied since 1935 (Bunn, 1935) and the theory of semiconductors got a firm start. The interest in ZnO is fueled and fanned by its direct wide band gap (Eg ~ 3.3 eV at 300 K), (Kakiuchi et al., 2006). ZnO also has much simpler crystal-growth technology, resulting in a potentially lower cost for ZnO base devices. ZnO has wide applications in the field of optoelectronics, (Kong & Wang, 2004) spintronics, (Sharma et al., 2003) piezoelectric

Greener Solvent-Free Reactions on ZnO 105

thiols are an important transformation in organic synthesis, (Greene & Wuts, 1999). Acylation of such functional groups is often necessary during the course of various transformations in a synthetic sequence, especially in the construction of poly functional

Hosseini-Sarvari and Sharghi, reported the acylation reaction of alcohols, phenols and amines under solvent-free conditions employing ZnO as catalyst (Scheme 2), (Hosseini-

ZnO, rt, solvent-free RXCOR'

R = alkyl and aryl; R' = Ph, Me; X=O, NH

The catalyst was successfully applied for acylation of a diverse range of alcohols, phenols and amines. In the case of alcohols and phenols, an acid chloride was preferred over the corresponding acidic anhydride. The reaction with acid anhydride was too slow to have practical application. Both primary and secondary alcohols react very well and tertiary alcohol is also acylated smoothly without any side products observed. Also, the reactions of amines with Ac2O were so fast in comparison to those of the aliphatic alcohols that the selective protection of an amine in the presence of aliphatic alcohols appeared to be a distinct

HO

Similarly, in another studies, *O-*acylation of alcohols and phenols with acid chlorides were performed employing ZnO and nano ZnO, (Moghaddam & Saeidian 2007; Tammaddon et

Recently, Bandgar and co-workers reported a convenient and efficient synthesis of thiol esters *via* the reaction of acyl chlorides with thiols using ZnO as catalyst under solvent-free conditions at room temperature. Major advantages associate with this protocol includes mild reaction conditions, short reaction time, excellent yields and recyclability of the

NHCOCH3

NHCOCH3

ZnO, rt, solvent-free (40 min., 90%)

(10 min., 90%)

(10 min., 87%)

possibility. Also, the amino group in aminophenol was selectivity acylated (Scheme 3).

molecules such as nucleosides, carbohydrates, steroids and natural products.

RXH RCOCl or (R'CO)2O

Scheme 2. Protection of alcohols, phenols, and amines by ZnO

ZnO, rt, solvent-free

HO NH2 HO NHCOPh (PhCO)2O

(MeCO)2O

NH2

NH2

Scheme 3. Selectivity in the protection by ZnO

catalyst, (Scheme 4) (Bandgar et al., 2009).

HO HO

Sarvari & Sharghi, 2005).

HO

al., 2005; Tayebee et al., 2010).

transducers, (Catti et al., 2003) and ultraviolet optoelectronics, (Wang et al., 2004). Consequently, ZnO is widely used as an additive into numerous materials and products including plastics, glass, rubber, ceramics, lubricants, paints, ointments, pigments, etc. In addition, with the development of industrialization, organic chemists have been confronted with a new challenge of finding novel methods in organic synthesis that can reduce and finally eliminate the impact of volatile organic solvents and hazardous toxic chemicals on the environment. So, use of non-toxic, environmentally friendly, and inexpensive solid catalysts to perform organic reactions has attracted considerable interest. Due to this, great efforts have been made by different research groups to achieve the goal of making the ZnO as catalyst in organic transformations. Interesting results have been achieved, such as the use of catalytic amounts of ZnO alone or mixed metals and metal oxides with ZnO as catalysts. In fact, ZnO as a heterogeneous catalysts can be easily separated from the reaction mixture and reused; it is generally not corrosive and do not produce problematic side products. Different classes of organic transformations have been studied and utilized using ZnO as heterogeneous catalysts, mainly exploited in the production of fine chemicals, is the subject of intensive studies in this area. Many catalytic ability of ZnO have been explored for various organic reactions facilitating synthesis of fine and specially chemicals. The application of ZnO catalyst not only is industrially important but also has academic merit. The present chapter review deal with the development in the use of ZnO as catalyst for a diverse range of organic transformations in solvent free conditions. Solvent-free organic reactions envisaged in the literature by utilizing ZnO catalyst are organized and are outline as below.

### **2. Solvent-free reactions catalyzed by ZnO**

#### **2.1 Friedel-Crafts acylation**

Aromatic ketones are valuable intermediates in the production of various fine chemicals, which are synthesized mainly by Friedel-Crafts acylation of aromatics with acid chlorides or carboxylic anhydrides (Jackson & Hargreaves, 2009). Traditionally, these reactions have been carried out using stoichiometric amounts of liquid Bronsted acids or Lewis acids. Also aromatic ketones are the valuable intermediates or final compounds used in the production of pharmaceuticals, cosmetics, agrochemicals, dyes, and specialty chemicals. Nowadays, the restrictions imposed by the waste-minimization laws and economic considerations driven to the development of new catalytic technologies. Modern processes are in fact, based on solid catalysts.

Different researcher groups have been reported that ZnO exhibit one of the best performance in the Friedel-Crafts acylation of various benzene derivatives in solvent freeconditions, (Ashoka et al., 2010; Hosseini-Sarvari & Sharghi, 2004; Thakuria et al., 2007; Wang et al., 2008), (Scheme 1).

$$\text{RCHO} + \text{Ar-H} \xrightarrow[\text{rt}, \text{solvent-free}]{\text{ZnO}} \text{ArCOR} + \text{HCl}$$

Scheme 1. Friedel-Crafts acylation on ZnO

#### **2.2 Protection reactions**

The use of protecting groups is very important in organic synthesis, often being the key for the success of many synthetic enterprises. The acylation of alcohols, phenols, amines, and

transducers, (Catti et al., 2003) and ultraviolet optoelectronics, (Wang et al., 2004). Consequently, ZnO is widely used as an additive into numerous materials and products including plastics, glass, rubber, ceramics, lubricants, paints, ointments, pigments, etc. In addition, with the development of industrialization, organic chemists have been confronted with a new challenge of finding novel methods in organic synthesis that can reduce and finally eliminate the impact of volatile organic solvents and hazardous toxic chemicals on the environment. So, use of non-toxic, environmentally friendly, and inexpensive solid catalysts to perform organic reactions has attracted considerable interest. Due to this, great efforts have been made by different research groups to achieve the goal of making the ZnO as catalyst in organic transformations. Interesting results have been achieved, such as the use of catalytic amounts of ZnO alone or mixed metals and metal oxides with ZnO as catalysts. In fact, ZnO as a heterogeneous catalysts can be easily separated from the reaction mixture and reused; it is generally not corrosive and do not produce problematic side products. Different classes of organic transformations have been studied and utilized using ZnO as heterogeneous catalysts, mainly exploited in the production of fine chemicals, is the subject of intensive studies in this area. Many catalytic ability of ZnO have been explored for various organic reactions facilitating synthesis of fine and specially chemicals. The application of ZnO catalyst not only is industrially important but also has academic merit. The present chapter review deal with the development in the use of ZnO as catalyst for a diverse range of organic transformations in solvent free conditions. Solvent-free organic reactions envisaged in the literature by utilizing

Aromatic ketones are valuable intermediates in the production of various fine chemicals, which are synthesized mainly by Friedel-Crafts acylation of aromatics with acid chlorides or carboxylic anhydrides (Jackson & Hargreaves, 2009). Traditionally, these reactions have been carried out using stoichiometric amounts of liquid Bronsted acids or Lewis acids. Also aromatic ketones are the valuable intermediates or final compounds used in the production of pharmaceuticals, cosmetics, agrochemicals, dyes, and specialty chemicals. Nowadays, the restrictions imposed by the waste-minimization laws and economic considerations driven to the development of new catalytic technologies. Modern processes are in fact, based on solid

Different researcher groups have been reported that ZnO exhibit one of the best performance in the Friedel-Crafts acylation of various benzene derivatives in solvent freeconditions, (Ashoka et al., 2010; Hosseini-Sarvari & Sharghi, 2004; Thakuria et al., 2007;

The use of protecting groups is very important in organic synthesis, often being the key for the success of many synthetic enterprises. The acylation of alcohols, phenols, amines, and

rt, solvent-freeArCOR + HCl

RCHO +Ar-H ZnO

ZnO catalyst are organized and are outline as below.

**2. Solvent-free reactions catalyzed by ZnO** 

**2.1 Friedel-Crafts acylation** 

Wang et al., 2008), (Scheme 1).

**2.2 Protection reactions** 

Scheme 1. Friedel-Crafts acylation on ZnO

catalysts.

thiols are an important transformation in organic synthesis, (Greene & Wuts, 1999). Acylation of such functional groups is often necessary during the course of various transformations in a synthetic sequence, especially in the construction of poly functional molecules such as nucleosides, carbohydrates, steroids and natural products.

Hosseini-Sarvari and Sharghi, reported the acylation reaction of alcohols, phenols and amines under solvent-free conditions employing ZnO as catalyst (Scheme 2), (Hosseini-Sarvari & Sharghi, 2005).

$$\text{RXH} \xrightarrow[\text{ZnO/rt/sol/t-free}]{\text{RCOCl or (R/CO)\_2O}} \text{RXCOR'}$$

R = alkyl and aryl; R' = Ph, Me; X=O, NH

Scheme 2. Protection of alcohols, phenols, and amines by ZnO

The catalyst was successfully applied for acylation of a diverse range of alcohols, phenols and amines. In the case of alcohols and phenols, an acid chloride was preferred over the corresponding acidic anhydride. The reaction with acid anhydride was too slow to have practical application. Both primary and secondary alcohols react very well and tertiary alcohol is also acylated smoothly without any side products observed. Also, the reactions of amines with Ac2O were so fast in comparison to those of the aliphatic alcohols that the selective protection of an amine in the presence of aliphatic alcohols appeared to be a distinct possibility. Also, the amino group in aminophenol was selectivity acylated (Scheme 3).

$$\gamma\_{\rm HO} \sim \text{NH}\_2 \xrightarrow[\text{ZnO, rt, solvent-free}]{(\text{PhCO})\_2\text{O}} \text{HO} \sim \text{NHCOPh} \text{ (40 \,\text{min.} , 90\%)}$$

Scheme 3. Selectivity in the protection by ZnO

Similarly, in another studies, *O-*acylation of alcohols and phenols with acid chlorides were performed employing ZnO and nano ZnO, (Moghaddam & Saeidian 2007; Tammaddon et al., 2005; Tayebee et al., 2010).

Recently, Bandgar and co-workers reported a convenient and efficient synthesis of thiol esters *via* the reaction of acyl chlorides with thiols using ZnO as catalyst under solvent-free conditions at room temperature. Major advantages associate with this protocol includes mild reaction conditions, short reaction time, excellent yields and recyclability of the catalyst, (Scheme 4) (Bandgar et al., 2009).

Greener Solvent-Free Reactions on ZnO 107

Entry Ar R1 R2 Time (min) Isolated Yields (%) 1 Ph CN CN 210 90 2 4-MeC6H4 CN CN 180 90 3 4-MeOC6H4 CN CN 150 90 4 2-MeOC6H4 CN CN 180 95 5 4-ClC6H4 CN CN 10 98 6 4-HOC6H4 CN CN 180 90 7 4-NO2C6H4 CN CN 10 98 8 3-ClC6H4 CN CN 180 90 9 2-ClC6H4 CN CN 30 90 10 2-Thienyl CN CN 120 90 11 4-Pyridyl CN CN 5 98 12 2- Furyl CN CN 180 95 13 4-ClC6H4 CN CO2Et 240 90 14 4-ClC6H4 CN OMe 1440 0 15 4-ClC6H4 CO2Et Cl 60 90 16 4-ClC6H4 CO2Et CO2Et 300 90 Table 1. Knoevenagel condensation using nano flake ZnO (0.004 g) at 25 oC under solvent-

strong acidic conditions to furnish 3,4-dihydropyrimidin-2(1*H*) was known as the Biginelli

Bahrami and co-workers reported a simple, efficient and practical procedure for the Biginelli reaction using ZnO as a novel and reusable catalyst under solvent-free conditions (Bahrami et al., 2009). The reaction proceeds efficiently under these conditions, and the

Described more than one century ago by Hantzsch, (Hantzsch, 1881) dialkyl 1,4-dihydro-2,6 dimethylpyridine-3,5-dicarboxylates (1,4-DHP) have now been recognized as vital drugs. 1,4-DHP derivatives possess a variety of biological activities such as vasodilator, bronchodilator, anti-atherosclerotic, anti-tumor, geroprotective, hepatoprotective and antidiabetic activity. In addition, recently preceding studies have suggested that 1,4-DHP

HN

Y

N H

R2

COR<sup>1</sup>

ketoester, and urea under

free conditions

reaction.

**2.4 Biginelli reaction** 

The three-component condensation reaction between aldehyde,

dihydropyrimidiones were produced in high yields (Scheme 7).

Y

NH2

Scheme 7. Solvent-free synthesis of dihydro pyrimidinones catalyzed by ZnO

<sup>+</sup> ZnO, neat, 80 oC, (8-35 min)

H2N

<sup>R</sup>2CHO <sup>+</sup> <sup>R</sup><sup>1</sup>

O

**2.5 Hantzsch condensation** 

O

Scheme 4. Synthesis of thiol esters using zinc oxide

In addition, ZnO as economical and heterogeneous catalyst was reported for the silylation of alcohols, phenols and naphthols (Shaterian & Ghashang, 2007) (Scheme 5).

$$\text{ROH} + \text{ (Me}\_3\text{Si)}\_2\text{NH} \xrightarrow[\text{Solvent-free, rt}]{\text{ZnO (cat.)}} \text{R-OTMS}$$

R= Aryl, primary, secondary, and tertiary aliphatic

Scheme 5. Silylation of alcohols, phenols, and naphthols using ZnO

#### **2.3 Knoevenagel condensations**

*Knoevenagel (*Knoevenagel, 1898) condensations which are one of the most important C-C bond forming reactions have been widely used in the synthesis of important intermediates or products for coumarin derivatives, cosmetics, perfumes, pharmaceuticals, calcium antagonists, and polymers.

Hosseini-Sarvari and co-workers (Hosseini-Sarvari et al., 2008) were reported that nano powder ZnO could be used as catalyst for *Knoevenagel* condensation. This condensation was performed using various aliphatic, aromatic, and heterocyclic aldehydes with malononitrile under solvent-free conditions in a one-step process. Most of the reactions investigated with nano ZnO catalysts were almost complete in 5 min to 3 h duration to produce the corresponding electrophilic alkenes in 90-98% yield (Scheme 6, and Table 1).

$$\underset{\text{Ar}}{\underset{\text{Ar}}{\bigtimes}} \overset{\text{O}}{\underset{\text{H}}{\bigtimes}}\_{\overset{\text{H}}{\underset{\text{solvent-free}}{\rightleftharpoons}}}^{\text{R}^{1}} \underset{\text{solvent-free}}{\underset{\text{solvent-free}}{\rightleftharpoons}} \underset{\text{R}^{1}}{\overset{\text{H}}{\underset{\text{Ar}}{\bigtimes}}}^{\text{H}}$$

Scheme 6. Knovenagel condensation using nano ZnO

R1, R2 = -Ph 94% R1 = -t-Bu R2 = -Et 76% R1 = -t-Bu R2 = -Ph 96% R1 = -Me R2 = -Ph 97% R1 = -Ph R2 = -Et 89% R1 = -p-ClC6H4 R2 = -Et 90% R1 = -p-OMeC6H4 R2 = -Et 90% R1 = -CH2Ph R2 = -Et 90% R1 = -p-NO2C6H4 R2 = -Ph 80%

R<sup>1</sup> S

HO

S

alcohols, phenols and naphthols (Shaterian & Ghashang, 2007) (Scheme 5).

Scheme 5. Silylation of alcohols, phenols, and naphthols using ZnO

O

In addition, ZnO as economical and heterogeneous catalyst was reported for the silylation of

Solvent-free, rt ROH (Me3Si)2NH R-OTMS

R= Aryl, primary, secondary, and tertiary aliphatic

*Knoevenagel (*Knoevenagel, 1898) condensations which are one of the most important C-C bond forming reactions have been widely used in the synthesis of important intermediates or products for coumarin derivatives, cosmetics, perfumes, pharmaceuticals, calcium

Hosseini-Sarvari and co-workers (Hosseini-Sarvari et al., 2008) were reported that nano powder ZnO could be used as catalyst for *Knoevenagel* condensation. This condensation was performed using various aliphatic, aromatic, and heterocyclic aldehydes with malononitrile under solvent-free conditions in a one-step process. Most of the reactions investigated with nano ZnO catalysts were almost complete in 5 min to 3 h duration to produce the

corresponding electrophilic alkenes in 90-98% yield (Scheme 6, and Table 1).

O nanoflake ZnO R<sup>1</sup>

+ rt

R<sup>2</sup> Ar

solvent-free

(5 mol%)

R<sup>2</sup> H

R1

Ar H

Scheme 6. Knovenagel condensation using nano ZnO

ZnO (cat.)

R R<sup>2</sup> <sup>2</sup> SH

ZnO, neat, 25 oC

O

ZnO, neat, 25 oC

Cl

Scheme 4. Synthesis of thiol esters using zinc oxide

+

**2.3 Knoevenagel condensations** 

antagonists, and polymers.

O

R<sup>1</sup> Cl

SH

HO

O


Table 1. Knoevenagel condensation using nano flake ZnO (0.004 g) at 25 oC under solventfree conditions

## **2.4 Biginelli reaction**

The three-component condensation reaction between aldehyde, ketoester, and urea under strong acidic conditions to furnish 3,4-dihydropyrimidin-2(1*H*) was known as the Biginelli reaction.

Bahrami and co-workers reported a simple, efficient and practical procedure for the Biginelli reaction using ZnO as a novel and reusable catalyst under solvent-free conditions (Bahrami et al., 2009). The reaction proceeds efficiently under these conditions, and the dihydropyrimidiones were produced in high yields (Scheme 7).

Scheme 7. Solvent-free synthesis of dihydro pyrimidinones catalyzed by ZnO

### **2.5 Hantzsch condensation**

Described more than one century ago by Hantzsch, (Hantzsch, 1881) dialkyl 1,4-dihydro-2,6 dimethylpyridine-3,5-dicarboxylates (1,4-DHP) have now been recognized as vital drugs. 1,4-DHP derivatives possess a variety of biological activities such as vasodilator, bronchodilator, anti-atherosclerotic, anti-tumor, geroprotective, hepatoprotective and antidiabetic activity. In addition, recently preceding studies have suggested that 1,4-DHP

Greener Solvent-Free Reactions on ZnO 109

nano flake ZnO exhibits the best performance in the phospha-Michael addition of

The authors were shown that, two kinds of ZnO (commercial ZnO and nano flake prepared ZnO, (20-30 nm)) were screened in the reaction between diethyphosphite and 2-((4 chlorophenyl)methylene)malononitrile (Table 3). As shown in Table 3, nano flake ZnO was found to be more effective than commercially ZnO in mediating the phospha Michael addition under solvent-free conditions. In order to examine the solvent effect and in quest for the deployment of a benign reaction medium, the reaction was explored in CH2Cl2, CH3CN, THF and water. The reaction in solvents required relatively longer reaction times

Entry Catalyst Solvent Time (min) Isolated Yield (%) 1 Commercially ZnO Non 120 80 2 Nano flake ZnO Non 30 98 3 Nano flake ZnO CH2Cl2 180 43 4 Nano flake ZnO CH3CN 180 40 5 Nano flake ZnO THF 180 40 6 Nano flake ZnO H2O 180 0

Table 3. Reaction between 2-((4-chlorophenyl)methylene)malononitrile with diethyl

Formamides are a class of important intermediates in organic synthesis. They have been widely used in the synthesis of pharmaceutically important compounds. A numerous methods have been reported for the formation of formamides (Green & Wuts, 1999). However, there are several factors such as low yield, difficulties in workup procedure and use of expensive reagents limiting their applications. This transformation was thoroughly

Recently, ZnO under solvent-free conditions have proved to be useful and reusable catalyst for *N-*formylation of amines using aqueous formic acid (85%) as formylating agent. This reaction was performed using various aliphatic, aromatic, heterocyclic primary and secondary amines under solvent-free conditions (Scheme 10) (Hosseini-Sarvari & Sharghi,

phosphite catalyzed by different crystallite of ZnO at 50 oC

nanoflake-ZnO

(5 mol %)

solvent free, 50 oC

unsaturated malonates under solvent-free conditions at 50

R1

R<sup>2</sup> (EtO)2P

O

Ar

phosphorus nucleophile to

oC (Scheme 9) (Hosseini-Sarvari & Etemad, 2008).

R2

+

R1 = CN; R2 = CN, CO2Et

Scheme 9. Phospha-Michael addition over nano ZnO

and afforded moderate yields of the product.

**2.7** *N***-Formylation of amines** 

investigated employing ZnO catalyst.

2006).

HP(O)(OEt)2

Ar R<sup>1</sup>

derivatives also provide an antioxidant protective effect that may contribute to their pharmacological activities. Oxidation of 1,4-DHP to pyridines has also been extensively studied. These examples clearly indicate the remarkable potential of novel 1,4-DHP and polyhydroquinoline derivatives as a source of valuable drug candidates and useful intermediates in organic chemistry. Many homogeneous and heterogeneous catalysts have been reported for the preparation of 1,4-DHP *via* the Hantzsch condensation, (Heravi et al., 2007; Kumar & Mauria, 2007).

Hantzsch condensation was thoroughly investigated employing ZnO catalyst, (Katkar et al., 2010, 2011; Moghaddam et al., 2009). Kassaee and co-workers employed ZnO nano particles as an efficient and heterogeneous catalyst for synthesis of polyhydroquinoline derivatives under solvent free conditions at room temperature (Kassaee et al., 2010). They were shown that in comparison with the same reaction catalyzed by commercially bulk ZnO (Moghaddam et al., 2009), use of ZnO nano particles reduced the reaction time with higher yields (Scheme 8).

Scheme 8. Hantsch condensation catalyzed by nano ZnO

The catalytic activity and the ability to recycle and reuse ZnO nano particles were studied in this system (Table 2). The catalyst was separated by centrifuging the aqueous layer at 3,000 rpm at 20 oC for 3 min, and was reused as such for subsequent experiments under similar reaction conditions.


Table 2. Reusability of the ZnO nano particles catalyst

### **2.6 Phospha-Michael addition**

Similar to the Michaelis-Arbuzov and the Michaelis-Becker reaction the phospha-Michael addition, *i.e.* the addition of a phosphorus nucleophile to an acceptor-substituted alkene or alkyne, certainly represents one of the most versatile and powerful tools for the formation of P-C bonds since many different electrophiles and P nucleophiles can be combined with each other. This offers the possibility to access many diversely functionalized products. This reaction was investigated employing nano ZnO catalyst. Hosseini-Sarvari et al.reported that

derivatives also provide an antioxidant protective effect that may contribute to their pharmacological activities. Oxidation of 1,4-DHP to pyridines has also been extensively studied. These examples clearly indicate the remarkable potential of novel 1,4-DHP and polyhydroquinoline derivatives as a source of valuable drug candidates and useful intermediates in organic chemistry. Many homogeneous and heterogeneous catalysts have been reported for the preparation of 1,4-DHP *via* the Hantzsch condensation, (Heravi et al.,

Hantzsch condensation was thoroughly investigated employing ZnO catalyst, (Katkar et al., 2010, 2011; Moghaddam et al., 2009). Kassaee and co-workers employed ZnO nano particles as an efficient and heterogeneous catalyst for synthesis of polyhydroquinoline derivatives under solvent free conditions at room temperature (Kassaee et al., 2010). They were shown that in comparison with the same reaction catalyzed by commercially bulk ZnO (Moghaddam et al., 2009), use of ZnO nano particles reduced the reaction time with higher

O O

RCHO

NH4OAc

The catalytic activity and the ability to recycle and reuse ZnO nano particles were studied in this system (Table 2). The catalyst was separated by centrifuging the aqueous layer at 3,000 rpm at 20 oC for 3 min, and was reused as such for subsequent experiments under similar

Run Yields (%) Recovery of nano ZnO (%)

Similar to the Michaelis-Arbuzov and the Michaelis-Becker reaction the phospha-Michael addition, *i.e.* the addition of a phosphorus nucleophile to an acceptor-substituted alkene or alkyne, certainly represents one of the most versatile and powerful tools for the formation of P-C bonds since many different electrophiles and P nucleophiles can be combined with each other. This offers the possibility to access many diversely functionalized products. This reaction was investigated employing nano ZnO catalyst. Hosseini-Sarvari et al.reported that

1 98 99 2 97 99 3 97 98 4 93 96

+

R' R' CN

ZnO nano <sup>+</sup> solvent-free, rt

O

R'

O

N H

O R O

2007; Kumar & Mauria, 2007).

yields (Scheme 8).

O R

N H

reaction conditions.

**2.6 Phospha-Michael addition** 

R'

NH2

ZnO nano solvent-free, rt

Scheme 8. Hantsch condensation catalyzed by nano ZnO

Table 2. Reusability of the ZnO nano particles catalyst

nano flake ZnO exhibits the best performance in the phospha-Michael addition of phosphorus nucleophile to unsaturated malonates under solvent-free conditions at 50 oC (Scheme 9) (Hosseini-Sarvari & Etemad, 2008).

$$\begin{array}{c} \stackrel{\text{R}^2}{\underset{\text{Ar}}{\overset{\text{R}^2}{\rightleftharpoons}}} \stackrel{\text{nanoflake-ZnO}}{\underset{\text{solvent}}{\overset{\text{(5 mol \text{\textdegree}}}{\longrightarrow}}} \stackrel{\text{nanoflake-ZnO}}{\underset{\text{solvent}}{\underset{\text{solvent}}{\overset{\text{(50)}}{\rightleftharpoons}}} \stackrel{\text{(EtO)}\_2\text{P}}{\underset{\text{Ar}}{\overset{\text{R}^2}{\rightleftharpoons}}} \stackrel{\text{\text{O}}^2}{\text{Ar}^2} $$

R1 = CN; R2 = CN, CO2Et

Scheme 9. Phospha-Michael addition over nano ZnO

The authors were shown that, two kinds of ZnO (commercial ZnO and nano flake prepared ZnO, (20-30 nm)) were screened in the reaction between diethyphosphite and 2-((4 chlorophenyl)methylene)malononitrile (Table 3). As shown in Table 3, nano flake ZnO was found to be more effective than commercially ZnO in mediating the phospha Michael addition under solvent-free conditions. In order to examine the solvent effect and in quest for the deployment of a benign reaction medium, the reaction was explored in CH2Cl2, CH3CN, THF and water. The reaction in solvents required relatively longer reaction times and afforded moderate yields of the product.


Table 3. Reaction between 2-((4-chlorophenyl)methylene)malononitrile with diethyl phosphite catalyzed by different crystallite of ZnO at 50 oC

#### **2.7** *N***-Formylation of amines**

Formamides are a class of important intermediates in organic synthesis. They have been widely used in the synthesis of pharmaceutically important compounds. A numerous methods have been reported for the formation of formamides (Green & Wuts, 1999). However, there are several factors such as low yield, difficulties in workup procedure and use of expensive reagents limiting their applications. This transformation was thoroughly investigated employing ZnO catalyst.

Recently, ZnO under solvent-free conditions have proved to be useful and reusable catalyst for *N-*formylation of amines using aqueous formic acid (85%) as formylating agent. This reaction was performed using various aliphatic, aromatic, heterocyclic primary and secondary amines under solvent-free conditions (Scheme 10) (Hosseini-Sarvari & Sharghi, 2006).

Greener Solvent-Free Reactions on ZnO 111

useful catalyst for the preparation of 2-oxazolines from carboxylic acids (Dotani, 1997;

Recently, Garcia-tellado and co-workers (Garcia-tellado et al., 2003) investigated the synthesis of 4, 4-disubstituted-2-oxazoline using ZnO in solvent-free microwave-assisted conditions. They were shown that zinc oxide was found to be the most efficient. It acts both as a solid support and as a soft Lewis acid catalyst. Other acidic solid supports (montmorillonites KSF and K10, calcinated Al2O3, SiO2) were unsuccessful. They also described that the zinc oxide seems to play a double role: it creates a polar environment for the microwave catalysis (polar solid support) and activates the carbonyl group for the

OH

Recently, a synthesized nano particle ZnO catalyzes the synthesis of benzimidazoles with formic acid in excellent yields (Scheme 13) (Alinezhad et al., 2012). Benzimidazoles are important natural and synthetic heterocyclic compounds. Some of their derivatives are marketed as antifungal, antihelmintic, and antipsychotic drugs and other derivatives have been found to possess some interesting bioactivities. The method which was reported by Alinezhad and co-workers avoids the use of expensive reagents and the reaction is performed under solvent-free condition, making it efficient and environmentally benign. The advantages of this method include the ease of preparation of nano particle ZnO; reusable, nontoxic, and inexpensive heterogeneous nano catalyst; mild reaction conditions;

ZnO-nps, 70 oC, solvent-free

<sup>R</sup> NH2 <sup>R</sup> <sup>N</sup>

Quinolines are well known for a wide range of medicinal properties being used as antimalarial, antiasthmatic, antihypertensive, antibacterial and tyrosine kinase inhibiting agent. Recently, the author reported syntheses wide range of quinolines have investigated by using nano ZnO as a heterogeneous solid catalyst under solvent-free condition (Scheme

ZnO, Mw -2H2O

N

R

O

H

N

R1 R2

R H <sup>2</sup> 2N

R1

Ishikawa, 1999; Morimoto & Ishikawa, 1997).

condensation (Lewis acid catalyst) (Scheme 12).

**2.10 Synthesis of benzimidazole derivatives** 

easy and clean workup; and convenient procedure.

+ HCO2H

Scheme 13. Synthesis of benzimidazoles by nano particle ZnO

NH2

**2.11 Synthesis of quinolines** 

14) (Hosseini-Sarvari, 2011).

R OH

+

Scheme 12. Synthesis of 4, 4-disubstituted-2-oxazoline using ZnO

O

RNHR' + HCO2H ZnO <sup>70</sup>oC, solvent-free <sup>R</sup> N R' O R= aryl, alkyl R'=aryl, alkyl, H

Scheme 10. *N*-Formylation of amines over ZnO

Also, prepared macroporous ZnO in presence of agar gel as template, later heated to 600 oC to produce the ZnO, has been used for the *N-*formylation of aniline (1 mmol) with formic acid (2.5 mmol) in solvent free conditions as indicated in Table 4 (Thakuria et al., 2007).


Table 4. Comparison of *N*-formylation of aniline (1 mmol) with formic acid (2.5 mmol) by using ZnO as catalyst

#### **2.8** *N***-Alkylation of imidazoles**

Imidazole-4-carboxaldehyde and 4-cyanoimidazole were *N*-benzylated and *N*-methylated using benzyl chloride and methyl iodide on ZnO under basic conditions without solvent (Oresmaa et al., 2007). Oresmaa et al. reported that Et3N or K2CO3 was added as base in the reaction on ZnO. They also investigated the effect of bases and catalyst on the product distribution of 1,4- and 1,5- substituted compounds (Scheme 11).

Scheme 11. *N-*Alkylation of imidazoles over ZnO

#### **2.9 Synthesis of oxazolines**

Oxazolines have been of great interest due to their versatility as protecting groups, as chiral auxiliaries in asymmetric synthesis, and as ligands for asymmetric catalysis. ZnO was a

Also, prepared macroporous ZnO in presence of agar gel as template, later heated to 600 oC to produce the ZnO, has been used for the *N-*formylation of aniline (1 mmol) with formic acid (2.5 mmol) in solvent free conditions as indicated in Table 4 (Thakuria et al., 2007).

Entry Catalyst Catalyst (mmol) Time (min) Isolated Yield (%) 1 Commercial ZnO 0.50 10 99 2 ZnO (macroporous) 0.50 08 99 3 ZnO (macroporous) 0.25 120 55

Table 4. Comparison of *N*-formylation of aniline (1 mmol) with formic acid (2.5 mmol) by

Imidazole-4-carboxaldehyde and 4-cyanoimidazole were *N*-benzylated and *N*-methylated using benzyl chloride and methyl iodide on ZnO under basic conditions without solvent (Oresmaa et al., 2007). Oresmaa et al. reported that Et3N or K2CO3 was added as base in the reaction on ZnO. They also investigated the effect of bases and catalyst on the product

<sup>N</sup> CHO

N

Bn

+

N

Bn

+

N H CN

N H CHO

41% (50:50)

50% (69:31)

N

N

Bn

<sup>N</sup> CN

Oxazolines have been of great interest due to their versatility as protecting groups, as chiral auxiliaries in asymmetric synthesis, and as ligands for asymmetric catalysis. ZnO was a

Bn

distribution of 1,4- and 1,5- substituted compounds (Scheme 11).

Bn-Cl ZnO, NEt3, 25 oC

ZnO, NEt3, 25 oC

CN Bn-Cl

Scheme 11. *N-*Alkylation of imidazoles over ZnO

<sup>70</sup>oC, solvent-free <sup>R</sup>

N R'

O

RNHR' + HCO2H ZnO

R= aryl, alkyl R'=aryl, alkyl, H

Scheme 10. *N*-Formylation of amines over ZnO

using ZnO as catalyst

N

N H

N

N H

**2.9 Synthesis of oxazolines** 

CHO

**2.8** *N***-Alkylation of imidazoles** 

useful catalyst for the preparation of 2-oxazolines from carboxylic acids (Dotani, 1997; Ishikawa, 1999; Morimoto & Ishikawa, 1997).

Recently, Garcia-tellado and co-workers (Garcia-tellado et al., 2003) investigated the synthesis of 4, 4-disubstituted-2-oxazoline using ZnO in solvent-free microwave-assisted conditions. They were shown that zinc oxide was found to be the most efficient. It acts both as a solid support and as a soft Lewis acid catalyst. Other acidic solid supports (montmorillonites KSF and K10, calcinated Al2O3, SiO2) were unsuccessful. They also described that the zinc oxide seems to play a double role: it creates a polar environment for the microwave catalysis (polar solid support) and activates the carbonyl group for the condensation (Lewis acid catalyst) (Scheme 12).

$$\underbrace{\text{O}}\_{\text{R}}\underbrace{\text{O}}\_{\text{OH}^{+}+\text{H}\_{2}\text{N}\xrightleftharpoons}\underbrace{\text{O}^{\text{H}}}\_{\text{R}^{1}}\underbrace{\text{ZnO}}\_{\text{-2H}\_{2}\text{O}}\underbrace{\text{N}^{1}}\_{\text{N}}\underbrace{\text{R}^{2}}\_{\text{N}}$$

Scheme 12. Synthesis of 4, 4-disubstituted-2-oxazoline using ZnO

#### **2.10 Synthesis of benzimidazole derivatives**

Recently, a synthesized nano particle ZnO catalyzes the synthesis of benzimidazoles with formic acid in excellent yields (Scheme 13) (Alinezhad et al., 2012). Benzimidazoles are important natural and synthetic heterocyclic compounds. Some of their derivatives are marketed as antifungal, antihelmintic, and antipsychotic drugs and other derivatives have been found to possess some interesting bioactivities. The method which was reported by Alinezhad and co-workers avoids the use of expensive reagents and the reaction is performed under solvent-free condition, making it efficient and environmentally benign. The advantages of this method include the ease of preparation of nano particle ZnO; reusable, nontoxic, and inexpensive heterogeneous nano catalyst; mild reaction conditions; easy and clean workup; and convenient procedure.

Scheme 13. Synthesis of benzimidazoles by nano particle ZnO

#### **2.11 Synthesis of quinolines**

Quinolines are well known for a wide range of medicinal properties being used as antimalarial, antiasthmatic, antihypertensive, antibacterial and tyrosine kinase inhibiting agent. Recently, the author reported syntheses wide range of quinolines have investigated by using nano ZnO as a heterogeneous solid catalyst under solvent-free condition (Scheme 14) (Hosseini-Sarvari, 2011).

Greener Solvent-Free Reactions on ZnO 113

Due to the biological activities of *α*-aminophosphonates, the search for new catalysts leading to an efficient and practical methodology for the synthesis of these compounds is highly desired. Kassaee et al. reported that zinc oxide nanoparticles were used as an effective catalyst in the solvent-free, three-component couplings of aldehydes, aromatic amines and dialkyl phosphites at room temperature to produce various *α*-amino phosphonates. Major advantages with this protocol include short reaction times, mild reaction conditions, easy

> PhNH2 ZnO (20 mol%),neat, 25 oC

More recently, the author has utilized the nano ZnO catalyst for synthesis of

Entry Catalyst Time (h) Conversion (%) Yield (%) 1 Bulky ZnO 12 90 84 2 Bulky Fe2O3 24 0 0 3 Bulky basic-Al2O3 12 49 45 4 Bulky CuO 24 6 Trace 5 Bulky MgO 24 0 0 6 Bulky CaO 24 0 0 7 Bulky TiO2 12 56 50 8 Nano TiO2 12 58 50 9 Nano MgO 24 0 0 10 Mg(ClO4)2 12 7 Trace 11 H3PW12O40 24 0 0 12 No catalyst 24 4 Trace 13 Nano ZnO 2 100 95 Table 6. Comparison of catalytic activity of nano ZnO catalyst with several other catalysts

aminophosphonic esters bearing a ferrocenyl moiety revealed that only few papers have been published on the synthesis of these compounds (Hosseini-Sarvari, 2011). To expand the scope of this novel transformation, the author used nano ZnO as catalyst for the synthesis of a range of new ferrocenyl aminophosphonates. A mechanistic proposal for the role of nano ZnO as the catalyst was also investigated. The activities of several other nano and bulky metal oxides and catalysts reported recently have been compared with nano ZnO. This study shows that the yield of desired product in the presence of nano ZnO is comparably

P

Ar

OR<sup>1</sup> OR<sup>1</sup>

O

NHPh


**2.13 Synthesis of** 

ArCHO +

higher than other catalysts used (Table 6).

**aminophosphonates** 

workup and generality (Scheme 16) (Kassaee et al., 2009).

O

OR<sup>1</sup> OR<sup>1</sup>

for the synthesis of diethyl anilino(ferrocenyl)methyl phosphonate

H P

Scheme 16. ZnO nanoparticle catalyzed the synthesis of

Scheme 14. Synthesis of quinolines catalyzed by nano ZnO

From Table 5, the author examined some other metal oxides in the synthesis of ethyl 2,4 dimethylquinoline-3-carboxylate. Also, in order to examine the solvent effect, the reaction was explored in toluene, THF, CH3CN, and water. The reaction in organic solvents required relatively longer reaction times and afforded trace yields of the product.


Table 5. Synthesis of ethyl 2,4-dimethylquinoline-3-carboxylate at 100 oC

#### **2.12 Synthesis of nitriles**

The cyano moiety is a highly important not only due to its synthetic value as precursor to other functionalities but also due to its presence in a variety of natural products, pharmaceuticals and novel materials. Although a plethora of methods are known for access to the cyano functionality, dehydration of aldoximes remains a convenient route. ZnO has been used for the synthesis of Nitriles from the dehydration of aldehydes under solvent-free conditions (Hosseini-Sarvari, 2005; Reddy & Pasha, 2010). The author reported the combination of ZnO and acetyl chloride accelerated the catalytic dehydration of aldoximes into nitriles dramatically (Scheme 15).

$$\text{R(Ar)CHO} \xrightarrow[\text{OH}^-]{\text{ZnO}} \text{R(Ar)CH=NOH} \xrightarrow[\text{R(O}^-)]{\text{ZnO}} \text{RCN}$$

Scheme 15. Synthesis of nitriles using ZnO

no solvent, 100 oC

From Table 5, the author examined some other metal oxides in the synthesis of ethyl 2,4 dimethylquinoline-3-carboxylate. Also, in order to examine the solvent effect, the reaction was explored in toluene, THF, CH3CN, and water. The reaction in organic solvents required

Entry Catalyst (mol %) Solvent Time (h) Isolated Yield (%) 1 Nano-flake ZnO (10) None 4 98 2 Nano-flake ZnO (10) Toluene 24 trace 3 Nano-flake ZnO (10) THF 24 trace 4 Nano-flake ZnO (10) CH3CN 24 trace 5 Nano-flake ZnO (10) H2O 24 0 6 Nano-flake ZnO (5) None 12 85 7 Nano-flake ZnO (2) None 24 67 8 Nano-flake ZnO (20) None 4 95 9 Nano-particle ZnO (10) None 12 80 10 Commercially ZnO (10) None 11 90 11 Commercially MgO (10) None 24 40 12 Commercially TiO2 (10) None 8 75 13 Commercially CaO (10) None 24 73

The cyano moiety is a highly important not only due to its synthetic value as precursor to other functionalities but also due to its presence in a variety of natural products, pharmaceuticals and novel materials. Although a plethora of methods are known for access to the cyano functionality, dehydration of aldoximes remains a convenient route. ZnO has been used for the synthesis of Nitriles from the dehydration of aldehydes under solvent-free conditions (Hosseini-Sarvari, 2005; Reddy & Pasha, 2010). The author reported the combination of ZnO and acetyl chloride accelerated the catalytic dehydration of aldoximes

R(Ar)CHO R(Ar)CH=NOH RCN NH2OH.HCl,

ZnO 80 oC N

R1

R2

R3

nano-flake ZnO (10 mol%)

NH2

R1

O

+

O R<sup>3</sup>

Scheme 14. Synthesis of quinolines catalyzed by nano ZnO

R2

relatively longer reaction times and afforded trace yields of the product.

Table 5. Synthesis of ethyl 2,4-dimethylquinoline-3-carboxylate at 100 oC

60 oC

ZnO

**2.12 Synthesis of nitriles** 

into nitriles dramatically (Scheme 15).

Scheme 15. Synthesis of nitriles using ZnO

#### **2.13 Synthesis of aminophosphonates**

Due to the biological activities of *α*-aminophosphonates, the search for new catalysts leading to an efficient and practical methodology for the synthesis of these compounds is highly desired. Kassaee et al. reported that zinc oxide nanoparticles were used as an effective catalyst in the solvent-free, three-component couplings of aldehydes, aromatic amines and dialkyl phosphites at room temperature to produce various *α*-amino phosphonates. Major advantages with this protocol include short reaction times, mild reaction conditions, easy workup and generality (Scheme 16) (Kassaee et al., 2009).

$$\begin{array}{c} \text{(ArCHO + H-} \underset{\underset{\text{OR}}{\overset{\text{-}}{\text{-}}} \text{OR}}{\overset{\text{-}}{\text{-}}} \text{OR} \text{-} \underset{\text{ZnO}}{\overset{\text{-}}{\text{ZnO}} \text{(20 mol\%)}} \text{,} \underset{\text{25}}{\overset{\text{-}}{\text{-}}} \text{\{\}}^{\text{NHPh}} \underset{\underset{\text{~}}{\overset{\text{-}}{\text{-}}} \text{\{}}^{\text{N}}}{\overset{\text{-}}{\text{-}}} \text{OR}^{1} \\ \text{OR}^{1} \end{array}$$

Scheme 16. ZnO nanoparticle catalyzed the synthesis of -amino phosphonates

More recently, the author has utilized the nano ZnO catalyst for synthesis of aminophosphonic esters bearing a ferrocenyl moiety revealed that only few papers have been published on the synthesis of these compounds (Hosseini-Sarvari, 2011). To expand the scope of this novel transformation, the author used nano ZnO as catalyst for the synthesis of a range of new ferrocenyl aminophosphonates. A mechanistic proposal for the role of nano ZnO as the catalyst was also investigated. The activities of several other nano and bulky metal oxides and catalysts reported recently have been compared with nano ZnO. This study shows that the yield of desired product in the presence of nano ZnO is comparably higher than other catalysts used (Table 6).


Table 6. Comparison of catalytic activity of nano ZnO catalyst with several other catalysts for the synthesis of diethyl anilino(ferrocenyl)methyl phosphonate

Greener Solvent-Free Reactions on ZnO 115

simplicity, neutral reaction conditions, reusability of the catalyst, avoidance of solvents, reduced environmental and economic impacts, and chemo selectivity. No toxic reagent or by product were involved and no laborious purifications were necessary (Hosseini-Sarvari

solvent-free

Amino alcohols are synthesized by acid catalyzed ring-opening of epoxides. Hosseini-Sarvari carried out the ring-opening of cyclohexene oxide, phenoxy oxide, styrene oxide,

alcohols catalyzed by ZnO, affording high yields of products under solvent-free conditions

ZnO (5 mol %)

amino alcohols catalyzed by ZnO

The Beckmann rearrangement is a fundamental and useful reaction, long recognized as an extremely valuable and versatile method for the preparation of amides or lactams, and often employed even in industrial processes. The conventional Beckmann rearrangement usually requires the use of strong Bronsted or Lewis acids, *i.e.* concentrated sulfuric acid, phosphorus pentachloride in diethyl ether, hydrogen chloride in acetic anhydride, causing large amounts of byproducts and serious corrosion problems. The ZnO catalyzed Beckmann rearrangement of various aldehydes and ketones in solvent-free conditions (Scheme 21) in good-to-excellent yields (60-95 %) (Sharghi & Hosseini, 2002). It was found that various types of aldehydes in the presence of ZnO were condensed cleanly, rapidly and selectively with hydroxylamine hydrochloride at 80°C in 5–15 min to afford the corresponding *Z*isomer of the oximes (OH *syn* to aryl) in excellent yields. Only a small amount of *E*-isomer*,* 

NH2OH.HCl <sup>R</sup><sup>2</sup>

R<sup>1</sup> ZnO,140-170 oC,

H N

O

solvent free, 70 oC <sup>R</sup>

ZnO

R1

O

H

Cl

R2

N H

OH

amino

rt

and epichlorohydrine oxide with various aromatic amines toward the synthesis of

and the reaction is also regioselective (Scheme 20) (Hosseini-Sarvari, 2008).

O R-NH2

+

+H R<sup>2</sup>

Scheme 19. Addition of acid chlorides to terminal alkynes, catalyzed by ZnO

& Mardaneh, 2011).

R<sup>1</sup> Cl

**2.17 Ring-opening of epoxides** 

Scheme 20. Synthesis of

**2.18 Beckmann rearrangement** 

*i.e.* ca. 10–20% was obtained. (Scheme 22).

R<sup>2</sup> R<sup>1</sup>

Scheme 21. Beckmann rearrangement catalyzed by ZnO

Solvent-free,

O

O

#### **2.14 Synthesis of bis(indolyl)methanes**

Bis(indolyl)methanes are the most active and highly recommended cruciferous substances for promoting beneficial estrogen metabolism and inducing apoptosis in human cancer cells. The electrophilic substitution reaction of indoles with aldehydes is one of the most simple and straightforward approaches for the synthesis of bis(indolyl)methanes. Hosseini-Sarvari successfully synthesized bis(indolyl) methanes by the reaction of indole with various aldehydes in the presence of ZnO catalyst in solvent-free conditions (Scheme 17). It was observed from this study that ZnO is an efficient catalyst for the synthesis of bis(indolyl)methanes in terms of product yields, reaction temperature, and reaction times ( Hosseini-Sarvari, 2008).

Scheme 17. Synthesis of bis(indolyl)methanes by ZnO

#### **2.15 Synthesis of** *N***-Sulfonylaldimines**

*N*-sulfonylimines have been increasing importance because they are one of the few types of electron-deficient imines that are stable enough to be isolated but reactive enough to undergo addition reactions. ZnO was reported as a mediated for preparations of *N*sulfonylimines under solvent-free conditions by conventional heating (Scheme 18). The advantages of this method are as follows: *i*) there is no need of toxic and waste producing Lewis acids; *ii*) work-up is simple; *iii*) the reaction procedure is not requiring specialized equipment; *iv*) zinc oxide powder can be re-used; and *v*) solvent-free condition (Hosseini-Sarvari & Sharghi, 2007).

Scheme 18. Preparations of *N*-sulfonylimines under solvent-free conditions by ZnO

#### **2.16 Synthesis of Chloro--unsaturated Ketones**

A useful reaction for the synthesis of Chloro--unsaturated unsaturated ketones (as synthetic intermediates particularly for the synthesis of heterocyclic systems) involves the addition of acid chloride derivatives to terminal alkynes. However, the addition of acid chlorides to alkynes often proceeds with concomitant decarbonylation. Recently, ZnO was shown a useful catalyst for the addition of acid chlorides to terminal alkynes, afforded (Z) adducts selectively without decarbonylation at room temperature under solvent-free conditions (Scheme 19). This protocol benefits from short reaction times, operational

Bis(indolyl)methanes are the most active and highly recommended cruciferous substances for promoting beneficial estrogen metabolism and inducing apoptosis in human cancer cells. The electrophilic substitution reaction of indoles with aldehydes is one of the most simple and straightforward approaches for the synthesis of bis(indolyl)methanes. Hosseini-Sarvari successfully synthesized bis(indolyl) methanes by the reaction of indole with various aldehydes in the presence of ZnO catalyst in solvent-free conditions (Scheme 17). It was observed from this study that ZnO is an efficient catalyst for the synthesis of bis(indolyl)methanes in terms of product yields, reaction temperature, and reaction times (

*N*-sulfonylimines have been increasing importance because they are one of the few types of electron-deficient imines that are stable enough to be isolated but reactive enough to undergo addition reactions. ZnO was reported as a mediated for preparations of *N*sulfonylimines under solvent-free conditions by conventional heating (Scheme 18). The advantages of this method are as follows: *i*) there is no need of toxic and waste producing Lewis acids; *ii*) work-up is simple; *iii*) the reaction procedure is not requiring specialized equipment; *iv*) zinc oxide powder can be re-used; and *v*) solvent-free condition (Hosseini-

ZnO

R<sup>1</sup> H

N

SO2R<sup>2</sup>


HN N

Ar

H

**2.14 Synthesis of bis(indolyl)methanes** 

10 mol% ZnO Ar

Scheme 17. Synthesis of bis(indolyl)methanes by ZnO

O

N H

<sup>2</sup> solvent free, 80 oC

R<sup>2</sup> + SO2NH2

110 o R<sup>1</sup> H C

Scheme 18. Preparations of *N*-sulfonylimines under solvent-free conditions by ZnO

**-unsaturated Ketones** 

Chloro-

synthetic intermediates particularly for the synthesis of heterocyclic systems) involves the addition of acid chloride derivatives to terminal alkynes. However, the addition of acid chlorides to alkynes often proceeds with concomitant decarbonylation. Recently, ZnO was shown a useful catalyst for the addition of acid chlorides to terminal alkynes, afforded (Z) adducts selectively without decarbonylation at room temperature under solvent-free conditions (Scheme 19). This protocol benefits from short reaction times, operational

Hosseini-Sarvari, 2008).

O

Sarvari & Sharghi, 2007).

**2.16 Synthesis of** 

A useful reaction for the synthesis of

**Chloro-**

H

**2.15 Synthesis of** *N***-Sulfonylaldimines** 

simplicity, neutral reaction conditions, reusability of the catalyst, avoidance of solvents, reduced environmental and economic impacts, and chemo selectivity. No toxic reagent or by product were involved and no laborious purifications were necessary (Hosseini-Sarvari & Mardaneh, 2011).

$$\bigcup\_{\mathbf{R}^1}^{\mathbf{O}} \underbrace{\llcorner}\_{\mathbf{Cl} + \mathbf{H} - \mathbf{H} - \mathbf{R}^2} \xrightarrow[\underset{\mathbf{rt}}{\mathbf{R}^2}]{\mathbf{ZnO}} \xrightarrow[\underset{\mathbf{R}^1}{\mathbf{R}^1}]{\mathbf{O}} \sideset{}{\mathbf{R}^1}$$

Scheme 19. Addition of acid chlorides to terminal alkynes, catalyzed by ZnO

#### **2.17 Ring-opening of epoxides**

Amino alcohols are synthesized by acid catalyzed ring-opening of epoxides. Hosseini-Sarvari carried out the ring-opening of cyclohexene oxide, phenoxy oxide, styrene oxide, and epichlorohydrine oxide with various aromatic amines toward the synthesis of amino alcohols catalyzed by ZnO, affording high yields of products under solvent-free conditions and the reaction is also regioselective (Scheme 20) (Hosseini-Sarvari, 2008).

Scheme 20. Synthesis of amino alcohols catalyzed by ZnO

#### **2.18 Beckmann rearrangement**

The Beckmann rearrangement is a fundamental and useful reaction, long recognized as an extremely valuable and versatile method for the preparation of amides or lactams, and often employed even in industrial processes. The conventional Beckmann rearrangement usually requires the use of strong Bronsted or Lewis acids, *i.e.* concentrated sulfuric acid, phosphorus pentachloride in diethyl ether, hydrogen chloride in acetic anhydride, causing large amounts of byproducts and serious corrosion problems. The ZnO catalyzed Beckmann rearrangement of various aldehydes and ketones in solvent-free conditions (Scheme 21) in good-to-excellent yields (60-95 %) (Sharghi & Hosseini, 2002). It was found that various types of aldehydes in the presence of ZnO were condensed cleanly, rapidly and selectively with hydroxylamine hydrochloride at 80°C in 5–15 min to afford the corresponding *Z*isomer of the oximes (OH *syn* to aryl) in excellent yields. Only a small amount of *E*-isomer*, i.e.* ca. 10–20% was obtained. (Scheme 22).

$$\mathop{\textstyle \underset{\text{R}^2}{\coprod}}^{\text{O}} \mathop{\textstyle \underset{\text{R}^1}{\underset{\text{NonO},140-170 \text{ }^\circ \text{C}}{\text{ZnO},140-170 \text{ }^\circ \text{C}}}^{\text{O}} \mathop{\textstyle \text{R}^1}\_{\text{N}^1} \mathop{\textstyle \text{R}^2}\_{\text{N}^2} \mathop{\textstyle \text{R}^1}\_{\text{O}} \mathop{\textstyle \text{R}^1}\_{\text{O}}$$

Scheme 21. Beckmann rearrangement catalyzed by ZnO

Greener Solvent-Free Reactions on ZnO 117

This chapter review describes various organic reactions on ZnO. During the past decades, numerous organic reactions have been developed using ZnO as a non-toxic metal oxide in response to the demand for more environmentally benign organic syntheses. This development promotes the use of ZnO because of its unique properties, as described in this review. ZnO appear to be attractive for conducting organic reactions in solvent-free condition, reusability of ZnO, especially nano ZnO. When a new reaction is discovered, a devoted chemist can no longer ignore the possibility of performing the reaction using the

In addition, many efforts could be found in the literature to improve the activity and stability of the ZnO catalysts, including promotion of the catalyst with transition metals like Pt, Pd, Fe, Mn, and etc. and mixed metal oxides such as TiO2, ZrO2, CaO, CuO, etc. which was not mentioned here. ZnO and its promoted versions are much more promising for various organic reactions of practical significance and are expected to gain great interest in

ZnO. Thus, ZnO is a new, useful, and powerful catalyst for organic reactions.

The author thank the Shiraz University Research Council for their financial support.

(September 2011), pp. 102-108, ISSN 0039-7911

No. 10, (April 2009), pp. 1801-1808, ISSN 0039-7911

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Bandgar, B. P., More, P. E., Kamble, V. T., & Sawant, S. S. (2009). Convenient and efficient

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**3. Conclusion** 

the coming years.

**5. References** 

**4. Acknowledgment** 

ISSN 0004-9425

$$\underset{\text{H}}{\underset{\text{H}}{\overset{\text{O}}{\text{N}}}} \underset{\text{H}}{\underset{\text{SO}}{\text{N}}} + \underset{\text{H}}{\underset{\text{NO}}{\overset{\text{N}}{\text{O}}}} \underset{\text{H}}{\underset{\text{NO}}{\text{N}}} \underset{\text{O}}{\underset{\text{O}}{\text{N}}} \text{-} \underset{\text{O}}{\underset{\text{O}}{\text{N}}} \text{-} \underset{\text{H}}{\underset{\text{O}}{\text{N}}}$$

Scheme 22. Synthesis of oximes catalyzed by ZnO

#### **2.19 Oxidation reactions**

Oxygen anions on metal oxide surfaces can act as Lewis as well as Brønsted bases. As such, they may oxidize adsorbed organics. The most common examples of such reactions in the metal oxide surface science literature are nucleophilic oxidations of carbonyl compounds. Aldehydes are oxidized to the corresponding carboxylates on a number of oxide surfaces such as ZnO. Higher alcohols and aldehydes also form carboxylate intermediates on ZnO (Vohs et al., 1986, 1988, 1989). Other related species such as esters exhibit similar chemistry; oxidation of methyl formate on the ZnO (001) surface (Scheme 23).

Scheme 23. Oxidation of methyl formate on the ZnO surface

Recently, a new synthetic method for the oxidation of sulfides on ZnO surface has been reported (Shiv et al*.,* 2009) in the presence of H2O2 under solvent-free conditions (Scheme 24). The results reveal that PANI/ZnO composite has high activity and selectivity compared to the raw ZnO.

$$\begin{array}{l} \stackrel{\text{\tiny\text{\tiny}}}{\text{\tiny}} \stackrel{\text{\tiny\text{\tiny}}}{\text{\tiny}} \text{\text{\tiny}}^{2} + 0.18 \text{-} 1 \text{ mol\text{\textquotedblleft}} \text{\textquotedblright} \text{ (ZnO/PAND)} \frac{1 \text{ mol\textquotedblright} \text{H}\_{2}\text{O}\_{2}}{\text{rt\textquotedblright} \text{solvent-free}} \text{\textquotedblleft} \text{\textquotedblleft} \text{\textquotedblright} \text{\textquotedblleft} \\\\ \stackrel{\text{\tiny\text{\tiny}}}{\text{R}^{2}} = \text{aryl, alkyl} \\\\ \stackrel{\text{\tiny\text{\tiny}}}{\text{R}^{2}} = \text{alkyl} \end{array}$$

Scheme 24. Selective oxidation of sulfide with ZnO

## **3. Conclusion**

116 Green Chemistry – Environmentally Benign Approaches

Oxygen anions on metal oxide surfaces can act as Lewis as well as Brønsted bases. As such, they may oxidize adsorbed organics. The most common examples of such reactions in the metal oxide surface science literature are nucleophilic oxidations of carbonyl compounds. Aldehydes are oxidized to the corresponding carboxylates on a number of oxide surfaces such as ZnO. Higher alcohols and aldehydes also form carboxylate intermediates on ZnO (Vohs et al., 1986, 1988, 1989). Other related species such as esters exhibit similar chemistry;

R H

R H

N OH

N HO

+

C O O

Zn

O

C O O

R

Zn

Recently, a new synthetic method for the oxidation of sulfides on ZnO surface has been reported (Shiv et al*.,* 2009) in the presence of H2O2 under solvent-free conditions (Scheme 24). The results reveal that PANI/ZnO composite has high activity and selectivity compared

<sup>R</sup><sup>2</sup> <sup>R</sup><sup>1</sup> <sup>S</sup>

<sup>R</sup> + 0.18-1 mol% (ZnO/PANI) <sup>2</sup> 1 mol% H2O2

rt, solvent-free

H

H

NH2OH.HCl

oxidation of methyl formate on the ZnO (001) surface (Scheme 23).

H2C O

+ZnO

R H

O


Scheme 23. Oxidation of methyl formate on the ZnO surface

ZnO, 80 oC, Solvent-free,

R H

Scheme 22. Synthesis of oximes catalyzed by ZnO

**2.19 Oxidation reactions** 

to the raw ZnO.

<sup>R</sup><sup>1</sup> <sup>S</sup>

R1 = aryl, alkyl R2 = alkyl

Scheme 24. Selective oxidation of sulfide with ZnO

O

This chapter review describes various organic reactions on ZnO. During the past decades, numerous organic reactions have been developed using ZnO as a non-toxic metal oxide in response to the demand for more environmentally benign organic syntheses. This development promotes the use of ZnO because of its unique properties, as described in this review. ZnO appear to be attractive for conducting organic reactions in solvent-free condition, reusability of ZnO, especially nano ZnO. When a new reaction is discovered, a devoted chemist can no longer ignore the possibility of performing the reaction using the ZnO. Thus, ZnO is a new, useful, and powerful catalyst for organic reactions.

In addition, many efforts could be found in the literature to improve the activity and stability of the ZnO catalysts, including promotion of the catalyst with transition metals like Pt, Pd, Fe, Mn, and etc. and mixed metal oxides such as TiO2, ZrO2, CaO, CuO, etc. which was not mentioned here. ZnO and its promoted versions are much more promising for various organic reactions of practical significance and are expected to gain great interest in the coming years.

## **4. Acknowledgment**

The author thank the Shiraz University Research Council for their financial support.

### **5. References**


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**7** 

**New Green Oil-Field Agents** 

The current state of environmental conditions on planet Earth is a substantial basis for modification as the cleaning and disposal of waste and emissions, and fundamental changes in processes and technology industries. Recently, the transition from administrative methods required to control unwanted emissions and destroy formed by chemical processes harmful substances to a fundamentally different method - the method of green chemistry. Green chemistry in its best incarnation - is an art form that allows not just to get the right stuff, but ideally to get it in a way, which does not harm the environment at any stage of

Like any perfected motion requires less force for its implementation and use of methods of green chemistry leads to a reduction of production costs, if only because they do not need to enter the stage of destruction and recycling of hazardous by-products, used solvents and other wastes, as they are simply not formed. Reducing the number of stages leading to energy savings, and this is also a positive impact on environmental and economic assessment of the production. It is important to note that the view of ongoing research from the viewpoint of green chemistry can be useful in purely scientific terms. Often, such a change of paradigm allows scientists to see their own research in a new light and open up

Introduction is a difficult task even for developed countries. In Britain, for example, is now a strongly encouraged interaction between scientists and chemical technologists. Even a joint center for the introduction of «green chemistry» has been created. At the University of Nottingham for the first time in the world to teach a course on green chemistry for chemistry students and chemists and technologists of the last school year. Undergraduates are taught to consider the chemical process as a whole and not fragmented. It is not enough that the specialist can choose the traditional or the most expensive reagent for the industrial synthesis, it is necessary to keep in mind the entire process from beginning to end. The primary sources of the initial reagent (extracted or renewable) as the reagent prepared, nuclear reaction efficiency, solvents, minimizing their use or non-toxic solvents, the selectivity of output allows the costs of by-products to be at a low level, what will ensure the

production. Of course, the substance itself must also be friendly to biosphere.

new opportunities that benefit science in general.

**2. How to implement "green" process** 

viability of the process.

**1. Introduction** 

Arkadiy Zhukov and Salavat Zaripov

*R&D Center, GC «Mirrico»* 

*Russian Federation* 


## **New Green Oil-Field Agents**

Arkadiy Zhukov and Salavat Zaripov *R&D Center, GC «Mirrico» Russian Federation* 

## **1. Introduction**

120 Green Chemistry – Environmentally Benign Approaches

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Vohs, J. M., & Barteau, M. A. (1988). Spectroscopic characterization of surface formates

*Surface Science,* Vol. 201, No. 3, (July 1988), pp. 481-502, ISSN 00396028 Vohs, J. M., & Barteau, M. A. (1988). Alkyl elimination from aldehydes on zinc oxide:

Vohs, J. M., & Barteau, M. A. (1989). Formation of stable alkyl and carboxylate intermediates

Vohs, J. M., & Barteau, M. A. (1989). Activation of aromatics on the polar surfaces of zinc

Wang, X. Ding, Y. Summers, C. J., & Wang, Z. L. (2004). Large-Scale Synthesis of Six-

Wang, R., Hong, X., & Shan, Z. (2008). A novel, convenient access to acylferrocenes:

*Letters*, Vol. 49, No. 4, (January 2008), pp. 636-641, ISSN 0040-4039

Vol. 183, No. 1, (February 2008), pp. 194-204, ISSN 1042-6507

ISSN 0039-7881

1566-7367

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ketones and aldehydes by zinc oxide. *Synthesis*, No. 8, (April 2002), pp. 1057-1060,

alcohols, phenols, and naphthols using HMDS in the presence of zinc oxide (ZnO) as economical heterogeneous catalyst. *Phosphorus Sulfur Silicon Related Elements*,

N. S. (2009). [PANI/ZnO] composite: Catalyst for solvent-free selective oxidation of sulfides. *Catalysis Communication*, Vol. 10, No. 6, (February 2009), pp. 905-912, ISSN

chemoselective *O*-acylation in the presence of zinc oxide as a heterogeneous, reusable and eco-friendly catalyst. *Tetrahedron Letters*, Vol. 46, No. 45, (Vovember

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produced via reaction of HCOOH and HCOOCH3 on the (0001) surface of zinc oxide. *Surface Science,* Vol. 197, No. 1-2, (January 1988), pp. 109-122, ISSN 00396028 Vohs, J. M., & Barteau, M. A. (1988). Reaction pathways and intermediates in the

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Nanometer-Wide ZnO Nanobelts*. Journal of Physical Chemistry: B*, Vol. 108, No. 26,

acylation of ferrocene with acyl chlorides in the presence of zinc oxide. *Tetrahedron* 

The current state of environmental conditions on planet Earth is a substantial basis for modification as the cleaning and disposal of waste and emissions, and fundamental changes in processes and technology industries. Recently, the transition from administrative methods required to control unwanted emissions and destroy formed by chemical processes harmful substances to a fundamentally different method - the method of green chemistry. Green chemistry in its best incarnation - is an art form that allows not just to get the right stuff, but ideally to get it in a way, which does not harm the environment at any stage of production. Of course, the substance itself must also be friendly to biosphere.

Like any perfected motion requires less force for its implementation and use of methods of green chemistry leads to a reduction of production costs, if only because they do not need to enter the stage of destruction and recycling of hazardous by-products, used solvents and other wastes, as they are simply not formed. Reducing the number of stages leading to energy savings, and this is also a positive impact on environmental and economic assessment of the production. It is important to note that the view of ongoing research from the viewpoint of green chemistry can be useful in purely scientific terms. Often, such a change of paradigm allows scientists to see their own research in a new light and open up new opportunities that benefit science in general.

## **2. How to implement "green" process**

Introduction is a difficult task even for developed countries. In Britain, for example, is now a strongly encouraged interaction between scientists and chemical technologists. Even a joint center for the introduction of «green chemistry» has been created. At the University of Nottingham for the first time in the world to teach a course on green chemistry for chemistry students and chemists and technologists of the last school year. Undergraduates are taught to consider the chemical process as a whole and not fragmented. It is not enough that the specialist can choose the traditional or the most expensive reagent for the industrial synthesis, it is necessary to keep in mind the entire process from beginning to end. The primary sources of the initial reagent (extracted or renewable) as the reagent prepared, nuclear reaction efficiency, solvents, minimizing their use or non-toxic solvents, the selectivity of output allows the costs of by-products to be at a low level, what will ensure the viability of the process.

New Green Oil-Field Agents 123

wastewater averaging 777 thousand m3, including cuttings 221.9 thousand m3. Significant damage to aquatic ecosystems causing a flowing drilling and drilling fluid from the barns, accidents at oil pipelines and fishing facilities. Accidents on main oil and gas pipelines have a catastrophic impact on the environment. However, most of the Russian pipelines operated by longer regulatory period, it makes them targets of environmental risk. Thus, in Russia on gas pipelines from 1960 to 1990, there were 1,200 accidents. The accident at the Western Siberian oil product in 1989 led to a major train accident, accompanied by a powerful explosion, fire, and many large-scale casualties. In 1994, as a result of an accident on an oil pipeline in the Komi Republic were contaminated with large surface area and significant volumes of oil got into streams and rivers. Oil and gas facilities emit greenhouse gases, nitrogen oxides, sulfur dioxide and other toxic and natural hydrocarbons themselves.

The structure of the oil is changed for the worse. Despite the advances in technology, methods, Geophysics, effort and investments aimed at exploration, a large-scale increase in lung stocks are not observed, but on the contrary, the future of oil production is associated with heavy oil onshore, offshore production (including the Arctic) and production of deepsea oil. Russian oil and gas producers are is the second largest country after Saudi Arabia. Currently in Russia there is a problem structure of proven oil reserves: the current oil reserves, the share of hard-to-oil exceeded 60%. In this regard, increased production of heavy oil: in 2005, was produced 42.5 million tons heavy and extra heavy oil. These are hard-to-oil, or mode of occurrence or the quality of raw materials. This category should also include most of the oil reserves in undergas deposits. If to this be added to the extraction yield in underdeveloped areas with difficult climatic conditions and the near absence of economic and transport infrastructure, the production could be on the verge of economic efficiency. To some extent, this is a world problem. The deterioration of the structure of

United States opened for the development of offshore deposits of the Pacific, Atlantic oceans, which have long been "locked up" officially "for environmental reasons." But after a major accident in the Gulf of Mexico in April 2010 on a platform of deep «Deep Horizon», Congress was forced to ban the further development of offshore fields until the development of regulations safety. There is no doubt that in the near future, the ban will be lifted, but the fact that the offshore fields have been opened for development, said that other more lucrative prospects of large-scale production in the U.S. has no land. In addition, in itself a step toward increasing production of deep oil suggests that the U.S. government are convinced that oil prices will remain high in the future, i.e. the proportion of hard-to-oil in

Renewable energy projects are actively promoted. The program of development of wind, solar and biofuels are set up all around the world. The leaders are the United States, China and the European Union. For example in Europe in 2020 is planned to increase the share of renewable energy to 20%. Officially this is because "the reduction of human impact on climate change and reducing emissions of CO2 in the atmosphere." But in order for these programs earned, and renewable energy has become competitive, you need high prices for oil and gas. A rise in prices, in turn, negatively affects economic growth. With all that research on human impacts on climate are controversial, as there was much talk, so to some extent is illogical rush to develop renewable energy (with the creation of objective difficulties for the economy). On the other hand, if we take into account the possibility of

inventories in the future will inevitably affect the price rise in oil

world production will increase.

## **3. Oil production**

Modern man can not exist without the consumption of large amounts of energy. Historical progress of the international community was determined by first of all that mankind has managed to use for practical purposes fossil fuels: coal, oil and natural gas. In the 60s of last century, about three-quarters of world consumption of fuel wood and covered with vegetable substitutes, almost a quarter - coal. The share of oil and gas accounted for about 1%. At the end of the century came the "era of coal." In 1900, its share in energy balance (FEB), the world has risen to 57%, the share of oil and gas was at 2.3% and 0.9%.

Until the mid-nineteenth century, oil was extracted in small amounts (2-5 tons per year) from shallow wells near its natural outlets to the surface. The Industrial Revolution, based on extensive use of steam engines, determined the broad demand for lubricants and light sources (kerosene). There was an increased demand for oil. With the introduction in the late 60-ies, oil well drilling global oil production tenfold increased from 2 to 20 million tonnes by the end of the nineteenth century. In 1900, oil was extracted in 10 countries: Russia, U.S., Dutch East India, Romania, Austria-Hungary, India, Japan, Canada, Germany, Peru. Almost half of total world oil production goes to Russia (9927 tonnes) and USA (8334 tonnes). Throughout the twentieth century. global oil consumption continued to grow rapidly.

The effectiveness of development of oil reduces the loss of its reserves in the subsoil, as not all stocks can be learned for technological reasons: falling well production rates (at least the fall of the reservoir pressure), water content and total depletion of deposits, etc. In order to increase production using different methods of influencing the oil reservoirs. So, in 1994, with the help of thermal, chemical, gas and other methods to increase the recovery factor in the world received an additional 93.4 million tons of oil. That same year, the application of new methods of enhanced oil recovery in the U.S. has allowed to obtain an additional 34.89 million tons, Russia - 11.55 million tonnes of oil. On Romashkino field through the use of enhanced oil recovery techniques more oil in 1993 was 26% with respect to all oil from the field in the same year. However, in recent years the average rate of oil recovery in Russia as a whole on all deposits decreased. Now in more than four fifths of all recoverable oil wells are produced fluids with electric-submersible pumps and gas lift.

## **4. Environmental issues in oil and gas sector**

Oil and gas industry has a negative impact on all components of the environment, especially in northern areas. During the drilling of wells, construction of buildings and land communications in areas of permafrost after the integrity of the protective vegetative cover increases the heating of the soil to great depth. Thermokarst processes cause melting of underground ice. Because of this, the formation of the earth surface subsidence, deep channels, gullies, formation of new lakes, marshes and valleys, which in turn increases the likelihood of deformation of the pipe and breaks. In the process of production, preparation, transportation, storage, processing and utilization of oil and gas produces toxic chemicals. Contain their bowels pollutes the waste water, natural landscapes and water bodies. Thus, in the West Siberian petroleum province in many areas of Ob river and its tributaries, the content of organic pollutants exceeds the MPC by ten times. The volume of water consumed by a drilling rig, for example, in the gas industry, ranging from 25 to 120 m3 per day. Daily volume of wastewater generated is 20-40 m3 per well. The annual volume of drilling

Modern man can not exist without the consumption of large amounts of energy. Historical progress of the international community was determined by first of all that mankind has managed to use for practical purposes fossil fuels: coal, oil and natural gas. In the 60s of last century, about three-quarters of world consumption of fuel wood and covered with vegetable substitutes, almost a quarter - coal. The share of oil and gas accounted for about 1%. At the end of the century came the "era of coal." In 1900, its share in energy balance

Until the mid-nineteenth century, oil was extracted in small amounts (2-5 tons per year) from shallow wells near its natural outlets to the surface. The Industrial Revolution, based on extensive use of steam engines, determined the broad demand for lubricants and light sources (kerosene). There was an increased demand for oil. With the introduction in the late 60-ies, oil well drilling global oil production tenfold increased from 2 to 20 million tonnes by the end of the nineteenth century. In 1900, oil was extracted in 10 countries: Russia, U.S., Dutch East India, Romania, Austria-Hungary, India, Japan, Canada, Germany, Peru. Almost half of total world oil production goes to Russia (9927 tonnes) and USA (8334 tonnes). Throughout the twentieth century. global oil consumption continued to grow rapidly.

The effectiveness of development of oil reduces the loss of its reserves in the subsoil, as not all stocks can be learned for technological reasons: falling well production rates (at least the fall of the reservoir pressure), water content and total depletion of deposits, etc. In order to increase production using different methods of influencing the oil reservoirs. So, in 1994, with the help of thermal, chemical, gas and other methods to increase the recovery factor in the world received an additional 93.4 million tons of oil. That same year, the application of new methods of enhanced oil recovery in the U.S. has allowed to obtain an additional 34.89 million tons, Russia - 11.55 million tonnes of oil. On Romashkino field through the use of enhanced oil recovery techniques more oil in 1993 was 26% with respect to all oil from the field in the same year. However, in recent years the average rate of oil recovery in Russia as a whole on all deposits decreased. Now in more than four fifths of all recoverable oil wells

Oil and gas industry has a negative impact on all components of the environment, especially in northern areas. During the drilling of wells, construction of buildings and land communications in areas of permafrost after the integrity of the protective vegetative cover increases the heating of the soil to great depth. Thermokarst processes cause melting of underground ice. Because of this, the formation of the earth surface subsidence, deep channels, gullies, formation of new lakes, marshes and valleys, which in turn increases the likelihood of deformation of the pipe and breaks. In the process of production, preparation, transportation, storage, processing and utilization of oil and gas produces toxic chemicals. Contain their bowels pollutes the waste water, natural landscapes and water bodies. Thus, in the West Siberian petroleum province in many areas of Ob river and its tributaries, the content of organic pollutants exceeds the MPC by ten times. The volume of water consumed by a drilling rig, for example, in the gas industry, ranging from 25 to 120 m3 per day. Daily volume of wastewater generated is 20-40 m3 per well. The annual volume of drilling

are produced fluids with electric-submersible pumps and gas lift.

**4. Environmental issues in oil and gas sector** 

(FEB), the world has risen to 57%, the share of oil and gas was at 2.3% and 0.9%.

**3. Oil production** 

wastewater averaging 777 thousand m3, including cuttings 221.9 thousand m3. Significant damage to aquatic ecosystems causing a flowing drilling and drilling fluid from the barns, accidents at oil pipelines and fishing facilities. Accidents on main oil and gas pipelines have a catastrophic impact on the environment. However, most of the Russian pipelines operated by longer regulatory period, it makes them targets of environmental risk. Thus, in Russia on gas pipelines from 1960 to 1990, there were 1,200 accidents. The accident at the Western Siberian oil product in 1989 led to a major train accident, accompanied by a powerful explosion, fire, and many large-scale casualties. In 1994, as a result of an accident on an oil pipeline in the Komi Republic were contaminated with large surface area and significant volumes of oil got into streams and rivers. Oil and gas facilities emit greenhouse gases, nitrogen oxides, sulfur dioxide and other toxic and natural hydrocarbons themselves.

The structure of the oil is changed for the worse. Despite the advances in technology, methods, Geophysics, effort and investments aimed at exploration, a large-scale increase in lung stocks are not observed, but on the contrary, the future of oil production is associated with heavy oil onshore, offshore production (including the Arctic) and production of deepsea oil. Russian oil and gas producers are is the second largest country after Saudi Arabia. Currently in Russia there is a problem structure of proven oil reserves: the current oil reserves, the share of hard-to-oil exceeded 60%. In this regard, increased production of heavy oil: in 2005, was produced 42.5 million tons heavy and extra heavy oil. These are hard-to-oil, or mode of occurrence or the quality of raw materials. This category should also include most of the oil reserves in undergas deposits. If to this be added to the extraction yield in underdeveloped areas with difficult climatic conditions and the near absence of economic and transport infrastructure, the production could be on the verge of economic efficiency. To some extent, this is a world problem. The deterioration of the structure of inventories in the future will inevitably affect the price rise in oil

United States opened for the development of offshore deposits of the Pacific, Atlantic oceans, which have long been "locked up" officially "for environmental reasons." But after a major accident in the Gulf of Mexico in April 2010 on a platform of deep «Deep Horizon», Congress was forced to ban the further development of offshore fields until the development of regulations safety. There is no doubt that in the near future, the ban will be lifted, but the fact that the offshore fields have been opened for development, said that other more lucrative prospects of large-scale production in the U.S. has no land. In addition, in itself a step toward increasing production of deep oil suggests that the U.S. government are convinced that oil prices will remain high in the future, i.e. the proportion of hard-to-oil in world production will increase.

Renewable energy projects are actively promoted. The program of development of wind, solar and biofuels are set up all around the world. The leaders are the United States, China and the European Union. For example in Europe in 2020 is planned to increase the share of renewable energy to 20%. Officially this is because "the reduction of human impact on climate change and reducing emissions of CO2 in the atmosphere." But in order for these programs earned, and renewable energy has become competitive, you need high prices for oil and gas. A rise in prices, in turn, negatively affects economic growth. With all that research on human impacts on climate are controversial, as there was much talk, so to some extent is illogical rush to develop renewable energy (with the creation of objective difficulties for the economy). On the other hand, if we take into account the possibility of

New Green Oil-Field Agents 125

Promising "green" platform for demulsifiers is glycerol. Ethoxylation its esters (acetate,

Despite the high efficiency of demulsifiers on the basis of alkyl phenols, their use should be

It was found that emulsions are efficient destroyers of silicone derivatives that do not contain toxic groups, such as phenolic or aryl. Such compounds are promising for use in oil

Leading manufacturers of oilfield chemicals have in their product line, "green" demulsifiers, for example, Clariant offers a similar product under the brand «Phasetreat». Are patented

There are patents in which as demulsifiers proposed use oligoglicosides containing alkyl radicals and oxyethylene-, oxypropylene-substituents. Specially negotiated their

Fig. 1. Abietic acids

Fig. 2. Synthesis of xylitol derivatives

stearate), a number of new demulsifiers.

field chemistry.

biodegradability.

limited due to toxicity of phenolic fragment.

cross-linked esters of glycerol and pentaerythritol.

reducing oil production in the next two decades, this increased interest in renewable energy is a logical and understandable.

## **5. Oilfield chemicals**

Significant branch of the modern chemical industry is the manufacture of products used in the processes of the oil and oil transportation. Each year the requirements for this kind of reagents increasingly tightened, for example, to decrease the volume of product flow while increasing its efficiency. Below we will consider some classes of oilfield chemicals and provide examples of available commercial products, including meeting the requirements of «green chemistry».

## **5.1 Demulsifiers**

In recent years, many deposits are opened in the late stage of development which has significant water content of the output.

As a result, commercial facilities pose serious technological challenges associated with the need to handle large quantities of water extracted simultaneously. Formation of emulsions during oil production is the main cause for large losses of oil, cost of transportation and preparation for recycling.

With increasing water content in oil at 1% of transportation costs increase by 3-5% for each transfer. In addition to costs directly in the oil industry, large volumes of water extracted along the way during transport cause the destruction of oilfield corrosion and environmental problems due to accidents of pipelines. Usually, the destruction of oil-water emulsion is heated addition of demulsifiers of this mixture.

Demulsifiers are currently anion (cation) active and nonionic surfactants: the block copolymers of ethylene oxide and propylene oxide, ethoxylated amines, higher fatty alcohols, alkylphenols, etc. Even with relatively low consumption of reagents (40-100 g/t) rather acute problem recycling of surface-active substances produced by many thousands of tons of the modern chemical industry.

Creating a "green" brands demulsifiers is justified not only environmental, but also with the economic position as a biodegradable agent does not require, or at least reduces the cost of cleanup and disposal of waste containing it. So do not consider the desire to create an "environmentally friendly" chemicals like fashion - it can actually lead to significant cost savings.

Here are some examples of such demulsifiers.

On the basis of wood chemical product manufacturing - tall oil, which consists of fatty acids (oleic, linoleic, palmitic) and resin acids: abietic, neoabietic, digidroabietic (Figure 1) by their ethoxylation demulsifiers were obtained, but tests showed their lower efficiency compared to demulsifier obtained ethoxylation of fatty acids.

On the basis of xylitol (derived from waste cotton plants, Figure 2) and synthetic fatty acids was obtained nonionic demulsifier, which showed a result of industrial tests of high efficiency.

reducing oil production in the next two decades, this increased interest in renewable energy

Significant branch of the modern chemical industry is the manufacture of products used in the processes of the oil and oil transportation. Each year the requirements for this kind of reagents increasingly tightened, for example, to decrease the volume of product flow while increasing its efficiency. Below we will consider some classes of oilfield chemicals and provide examples of available commercial products, including meeting the requirements of

In recent years, many deposits are opened in the late stage of development which has

As a result, commercial facilities pose serious technological challenges associated with the need to handle large quantities of water extracted simultaneously. Formation of emulsions during oil production is the main cause for large losses of oil, cost of transportation and

With increasing water content in oil at 1% of transportation costs increase by 3-5% for each transfer. In addition to costs directly in the oil industry, large volumes of water extracted along the way during transport cause the destruction of oilfield corrosion and environmental problems due to accidents of pipelines. Usually, the destruction of oil-water

Demulsifiers are currently anion (cation) active and nonionic surfactants: the block copolymers of ethylene oxide and propylene oxide, ethoxylated amines, higher fatty alcohols, alkylphenols, etc. Even with relatively low consumption of reagents (40-100 g/t) rather acute problem recycling of surface-active substances produced by many thousands of

Creating a "green" brands demulsifiers is justified not only environmental, but also with the economic position as a biodegradable agent does not require, or at least reduces the cost of cleanup and disposal of waste containing it. So do not consider the desire to create an "environmentally friendly" chemicals like fashion - it can actually lead to significant cost

On the basis of wood chemical product manufacturing - tall oil, which consists of fatty acids (oleic, linoleic, palmitic) and resin acids: abietic, neoabietic, digidroabietic (Figure 1) by their ethoxylation demulsifiers were obtained, but tests showed their lower efficiency compared

On the basis of xylitol (derived from waste cotton plants, Figure 2) and synthetic fatty acids was obtained nonionic demulsifier, which showed a result of industrial tests of high

is a logical and understandable.

significant water content of the output.

tons of the modern chemical industry.

Here are some examples of such demulsifiers.

to demulsifier obtained ethoxylation of fatty acids.

savings.

efficiency.

emulsion is heated addition of demulsifiers of this mixture.

**5. Oilfield chemicals** 

«green chemistry».

**5.1 Demulsifiers** 

preparation for recycling.

Fig. 1. Abietic acids

Fig. 2. Synthesis of xylitol derivatives

Promising "green" platform for demulsifiers is glycerol. Ethoxylation its esters (acetate, stearate), a number of new demulsifiers.

Despite the high efficiency of demulsifiers on the basis of alkyl phenols, their use should be limited due to toxicity of phenolic fragment.

It was found that emulsions are efficient destroyers of silicone derivatives that do not contain toxic groups, such as phenolic or aryl. Such compounds are promising for use in oil field chemistry.

Leading manufacturers of oilfield chemicals have in their product line, "green" demulsifiers, for example, Clariant offers a similar product under the brand «Phasetreat». Are patented cross-linked esters of glycerol and pentaerythritol.

There are patents in which as demulsifiers proposed use oligoglicosides containing alkyl radicals and oxyethylene-, oxypropylene-substituents. Specially negotiated their biodegradability.

New Green Oil-Field Agents 127

The vast majority of demulsifiers are oxyalkylated derivatives (poly-) alcohols, acids and amines. Search and development of new products should be the rational choice of the starting material - the basis platform for oxyalkylation. Careful attention should be paid to renewable raw materials and waste paper and pulp, wood chemistry and food industry.

In addition to chemical methods of destruction of water-oil emulsions to improve and develop new techniques based on physical effects: heat, magnetic field, etc., as well as use the combined, integrated approach - the use of demulsifiers in conjunction with the

To date, corrosion processes create huge problems of the world economy. The most conservative estimate of about 10% annually smelted metal is to replenish losses due to corrosion. However, the main corrosion damage not associated with loss of large amounts of metal, but with the failure of themselves metal products and structures as a result of loss of essential properties (strength, ductility, electrical conductivity, tightness, thermal conductivity, etc.). Protecting metals from corrosion - a global international problem, so in all developed countries attached great importance to anti-corrosion materials in all its

1. Design, manufacture and application of corrosion-resistant materials for the

2. Create a corrosion-resistant coatings and methods and technologies for processing of

manifestations. At present there five areas to combat the corrosion of metals:

manufacture of pipelines and process equipment

material surfaces exposed to the corrosive effect 3. Creation and application of corrosion inhibitors

Fig. 5. The spatial configuration of calix [4] arene

hydrodynamic effects and magnetic devices.

**5.2 Corrosion inhibitors** 

Demulsifier, patented Nalco (Figure 3) is not only biodegradable but also non-toxic compound.

Fig. 3. Nalco' s demulsifier

The new direction is the use of dendrimers as demulsifiers, polyesters such as oxyalkylated Boltorn H20 and similar compounds (Figure 4).

Fig. 4. Dendritic demulsifier

Despite the apparent complexity of its synthesis is rather simple.

Among the macromolecular platforms for the synthesis of interest are the macrocycles, such as calix[4]arenes. The possibility of fixing the macrocyclic rings in several spatial configurations, which provides a different position of substituents in space relative to each other (Figure 5), in combination with non-toxicity and ease of chemical modification of the lower rim of calixarenes makes promising molecular platforms for the creation on their basis of various reagents. Although many authors noted non-toxic derivatives of calixarene, yet the question of their biodegradability and metabolism studied enough; phenolic fragments, forming a skeleton macromolecules suggest that the degradation products could be toxic substances.

Demulsifier, patented Nalco (Figure 3) is not only biodegradable but also non-toxic

The new direction is the use of dendrimers as demulsifiers, polyesters such as oxyalkylated

Among the macromolecular platforms for the synthesis of interest are the macrocycles, such as calix[4]arenes. The possibility of fixing the macrocyclic rings in several spatial configurations, which provides a different position of substituents in space relative to each other (Figure 5), in combination with non-toxicity and ease of chemical modification of the lower rim of calixarenes makes promising molecular platforms for the creation on their basis of various reagents. Although many authors noted non-toxic derivatives of calixarene, yet the question of their biodegradability and metabolism studied enough; phenolic fragments, forming a skeleton macromolecules suggest that the degradation products could be toxic substances.

compound.

Fig. 3. Nalco' s demulsifier

Fig. 4. Dendritic demulsifier

Despite the apparent complexity of its synthesis is rather simple.

Boltorn H20 and similar compounds (Figure 4).

Fig. 5. The spatial configuration of calix [4] arene

The vast majority of demulsifiers are oxyalkylated derivatives (poly-) alcohols, acids and amines. Search and development of new products should be the rational choice of the starting material - the basis platform for oxyalkylation. Careful attention should be paid to renewable raw materials and waste paper and pulp, wood chemistry and food industry.

In addition to chemical methods of destruction of water-oil emulsions to improve and develop new techniques based on physical effects: heat, magnetic field, etc., as well as use the combined, integrated approach - the use of demulsifiers in conjunction with the hydrodynamic effects and magnetic devices.

## **5.2 Corrosion inhibitors**

To date, corrosion processes create huge problems of the world economy. The most conservative estimate of about 10% annually smelted metal is to replenish losses due to corrosion. However, the main corrosion damage not associated with loss of large amounts of metal, but with the failure of themselves metal products and structures as a result of loss of essential properties (strength, ductility, electrical conductivity, tightness, thermal conductivity, etc.). Protecting metals from corrosion - a global international problem, so in all developed countries attached great importance to anti-corrosion materials in all its manifestations. At present there five areas to combat the corrosion of metals:


New Green Oil-Field Agents 129

It is known that the salts of chromium (III) are used as components of an effective corrosion inhibitors of metal products, but their use should be limited due to toxicity. Creating a less risky alternative to trains - the use of titanium salts in combination with oxidants such as hydrogen peroxide and the use of mono-, oligo-and polysaccharides as film-forming component. Described as an inhibitor of the phosphoric and boric acids with much less

The problem of corrosion protection equipment, operated in hostile environments such as seawater, is quite serious. Offshore drilling and production of oil and gas offshore require not only high but also low toxicity and biodegradable oil-reagent did not affect the indigenous inhabitants of the marine flora and fauna. Found that many of the known corrosion inhibitors, even at a concentration of less than 1 ppm inhibit the growth of algae. Preferably, the inhibitor is biodegradable at least 60% within 28 days after release to the environment. Also an important requirement is that sufficient hydrophilicity to minimize the bioaccumulation in adipose tissue, since lipophilic substances tend to accumulate as they

Established that the imidazolines are not only effective inhibitors of corrosion, but also promising from an environmental point of view of satisfying the rigorous standards of toxicity. They do not contain phosphorus and sulfur atoms, and therefore are considered more "environmentally friendly". However, this does not mean that the substance is

One of the leading companies engaged in the development and manufacture of oilfield

In the product line, the Russian company also has Mirrico anticorrosive agents on the basis

To protect the equipment with high concentrations of hydrogen sulfide and carbon dioxide proposed a corrosion inhibitor, which is a cyclic lactone (Figure 8) disaccharide ester and fatty acid obtained by enzymatic synthesis using the culture of *Torulopsis apicola* relevant material: oligo-and polysaccharides, saturated / unsaturated fatty acids oils, fats and other

Along with a significant inhibitory effect observed with the following positive aspects: easy dispersibility in water, good adsorption on metal surfaces for values of pH 5.3 or lower,

non-inflammability and significantly less toxicity compared to known inhibitors.

chemicals - Baker Huges proposed as corrosion inhibitors imidazolines (Figure 7)

completely harmless, it is a very low toxicity at relevant concentrations.

Fig. 7. Imidazoline derivatives- corrosion inhibitors

of imidazolines on brand Scimol.

substances of plant or animal origin.

toxicity.

move up the food chain.


Since the purpose of corrosion inhibitors do not exist, they are almost for each specific system, so the range of developed and produced by inhibitors of the world is enormous. In this world of science and technology known to more than 300000 names of individual chemicals and various technical formulations are classified as corrosion inhibitors. The volume of world production and consumption of corrosion inhibitors, lubricant additives is 4.4 million tons/year with a growth trend 5.5-6.0 million tons/year. Of this amount: the inhibition of oil, gas, produced water and other environments in oil and gas industry - 20- 25%, the preparation and processing of oil - 2-5%, the inhibition of oil production and protection of oil-based, 65-75% for other needs (inhibition of acid cooling media, etc.) - 3-5%. A large number of inhibitors used in pipeline transportation.

Corrosion inhibitors are the most diverse classes of organic and inorganic compounds, most of which is synthetic, not naturally occurring. It is obvious that the negative impact on the biosphere biologically hostile, recalcitrant compounds can not be overestimated, especially in a wide range of use of a reagent. The problem of corrosion of equipment, in particular oil field, is successfully solved, but to date there is no product that simultaneously satisfies all the requirements of the requirements: high efficiency, low cost, versatility and environmental safety. In light of this ever being the development of new corrosion inhibitors, which would be advantageous to differ from the existing not only the efficiency of inhibition, but also environmental safety.

For example, a corrosion inhibitor designed on the basis of waste vegetable oil that contains no toxic compounds and are low cost at a degree of protection of 78-95% depending on the environment.

BASF's proposed "green" corrosion inhibitors based on propargyl alcohol, known under the trade name Korantin ® PM (Figure 6).

Fig. 6. BASF's corrosion inhibitors

Their most significant differences is not only cheap and nontoxic, but high inhibitory activity, 2-3 times exceeding some used products.

Company Cortec patented volatile corrosion inhibitor, a major component of which is ammonium benzoate - a non-toxic compound to the environment. The use of such compounds is justified in the manufacture of new modern packaging materials to prevent not only mechanical damage and corrosion of metal products during transportation and storage.

4. The use of electrochemical methods of protection of process equipment, pipelines and

5. The package of measures for the development, design, construction and operation of pipelines and processing equipment in order to avoid the stress state of metal in which

Since the purpose of corrosion inhibitors do not exist, they are almost for each specific system, so the range of developed and produced by inhibitors of the world is enormous. In this world of science and technology known to more than 300000 names of individual chemicals and various technical formulations are classified as corrosion inhibitors. The volume of world production and consumption of corrosion inhibitors, lubricant additives is 4.4 million tons/year with a growth trend 5.5-6.0 million tons/year. Of this amount: the inhibition of oil, gas, produced water and other environments in oil and gas industry - 20- 25%, the preparation and processing of oil - 2-5%, the inhibition of oil production and protection of oil-based, 65-75% for other needs (inhibition of acid cooling media, etc.) - 3-5%.

Corrosion inhibitors are the most diverse classes of organic and inorganic compounds, most of which is synthetic, not naturally occurring. It is obvious that the negative impact on the biosphere biologically hostile, recalcitrant compounds can not be overestimated, especially in a wide range of use of a reagent. The problem of corrosion of equipment, in particular oil field, is successfully solved, but to date there is no product that simultaneously satisfies all the requirements of the requirements: high efficiency, low cost, versatility and environmental safety. In light of this ever being the development of new corrosion inhibitors, which would be advantageous to differ from the existing not only the efficiency

For example, a corrosion inhibitor designed on the basis of waste vegetable oil that contains no toxic compounds and are low cost at a degree of protection of 78-95% depending on the

BASF's proposed "green" corrosion inhibitors based on propargyl alcohol, known under the

Their most significant differences is not only cheap and nontoxic, but high inhibitory

Company Cortec patented volatile corrosion inhibitor, a major component of which is ammonium benzoate - a non-toxic compound to the environment. The use of such compounds is justified in the manufacture of new modern packaging materials to prevent not only mechanical damage and corrosion of metal products during transportation and

underground utilities in general

the corrosion processes are significantly faster.

A large number of inhibitors used in pipeline transportation.

of inhibition, but also environmental safety.

trade name Korantin ® PM (Figure 6).

Fig. 6. BASF's corrosion inhibitors

activity, 2-3 times exceeding some used products.

environment.

storage.

It is known that the salts of chromium (III) are used as components of an effective corrosion inhibitors of metal products, but their use should be limited due to toxicity. Creating a less risky alternative to trains - the use of titanium salts in combination with oxidants such as hydrogen peroxide and the use of mono-, oligo-and polysaccharides as film-forming component. Described as an inhibitor of the phosphoric and boric acids with much less toxicity.

The problem of corrosion protection equipment, operated in hostile environments such as seawater, is quite serious. Offshore drilling and production of oil and gas offshore require not only high but also low toxicity and biodegradable oil-reagent did not affect the indigenous inhabitants of the marine flora and fauna. Found that many of the known corrosion inhibitors, even at a concentration of less than 1 ppm inhibit the growth of algae. Preferably, the inhibitor is biodegradable at least 60% within 28 days after release to the environment. Also an important requirement is that sufficient hydrophilicity to minimize the bioaccumulation in adipose tissue, since lipophilic substances tend to accumulate as they move up the food chain.

Established that the imidazolines are not only effective inhibitors of corrosion, but also promising from an environmental point of view of satisfying the rigorous standards of toxicity. They do not contain phosphorus and sulfur atoms, and therefore are considered more "environmentally friendly". However, this does not mean that the substance is completely harmless, it is a very low toxicity at relevant concentrations.

One of the leading companies engaged in the development and manufacture of oilfield chemicals - Baker Huges proposed as corrosion inhibitors imidazolines (Figure 7)

Fig. 7. Imidazoline derivatives- corrosion inhibitors

In the product line, the Russian company also has Mirrico anticorrosive agents on the basis of imidazolines on brand Scimol.

To protect the equipment with high concentrations of hydrogen sulfide and carbon dioxide proposed a corrosion inhibitor, which is a cyclic lactone (Figure 8) disaccharide ester and fatty acid obtained by enzymatic synthesis using the culture of *Torulopsis apicola* relevant material: oligo-and polysaccharides, saturated / unsaturated fatty acids oils, fats and other substances of plant or animal origin.

Along with a significant inhibitory effect observed with the following positive aspects: easy dispersibility in water, good adsorption on metal surfaces for values of pH 5.3 or lower, non-inflammability and significantly less toxicity compared to known inhibitors.

New Green Oil-Field Agents 131

As a result of flooding of the output at all stages of oil is the formation of salt deposits. Accumulating in the production strings on the surface of downhole pumping equipment and systems infield collection and preparation of oil, salt deposits not only cause great material

The effectiveness of measures to combat the deposition of salt depends on an integrated approach to solving this problem. Need to know the physical and chemical processes and the causes of salt formation, taking into account the geological and physical conditions of occurrence of oil, human events and features of the development of oil and gas deposits and operating wells. The key areas for the deposition of salts from oil should be warning them, as a permanent measure, based on the best technological solutions that require scientific and

Based on the economic viability, depending on the conditions and characteristics of reservoir development, availability of raw materials, availability of technical resources and other factors may have different ways of dealing with this phenomenon, but in practice the problem of oil-field warning of salt deposits is decided mainly by inhibitor protection of

Historically, the dominant classes of products inhibiting scaling in oil and gas production were phosphorous substances (eg aminomethylenephosphonates and phosphonic acids) and synthetic water soluble polymers such as polimaleates, polyacrylates, polisulfonates. Their main disadvantages are toxic to the environment and bioundegradability. The use of both classes of inhibitors are more tightly constrained as a result of legislative control. In recent years, the market introduced the latest "green" inhibitors: poly (amino acid) and chemically enhanced natural materials. This class of products has a low environmental toxicity, but the use of these inhibitors is still low because of the difficulty of their synthesis

Company AkzoNobel has been developed a new class of materials - hybrid polymers (copolymers of polysaccharides and polycarboxylic acids), (Figure 9) which combine the advantages of a single molecule, and synthetic and natural materials, the lack of benefit

costs in the process of removing them, but also to a significant loss in oil production.

methodological generalizations and systematic approach.

and significant economic costs compared with existing technologies.

other than some of the restrictions currently known "green" products.

wells and equipment .

Fig. 9. AkzoNobel's hybrid polymers

Fig. 8. Corrosion inhibitors based on oligo-and polysaccharides

Despite the variety of substances used as corrosion inhibitors, the most promising in terms of 'green' chemistry, are substances of natural origin and their various derivatives.

One of the main features of oilfield chemicals is their variety, caused by various conditions of oil production, changing the composition of crude oil and its associated waters. It often happens that the composition of oil in the well is so unique that it has required the selection of specific agents with the optimal dose is for a particular hole. The problem of corrosion of oilfield equipment depends on the chemical composition of the medium in which it is located: it is saturated salt solutions and contain significant amounts of hydrogen sulfide and mercaptans, water-oil emulsion and produced water with dissolved carbon dioxide, so the selection and creation of appropriate reagents is often a nontrivial task.

#### **5.3 Scale inhibitors**

The present stage of oil production is characterized by the need to make the surface of the vast amounts of associated water reservoir as well as injected in the reservoir to maintain pressure.

Fig. 8. Corrosion inhibitors based on oligo-and polysaccharides

Despite the variety of substances used as corrosion inhibitors, the most promising in terms

One of the main features of oilfield chemicals is their variety, caused by various conditions of oil production, changing the composition of crude oil and its associated waters. It often happens that the composition of oil in the well is so unique that it has required the selection of specific agents with the optimal dose is for a particular hole. The problem of corrosion of oilfield equipment depends on the chemical composition of the medium in which it is located: it is saturated salt solutions and contain significant amounts of hydrogen sulfide and mercaptans, water-oil emulsion and produced water with dissolved carbon dioxide, so

The present stage of oil production is characterized by the need to make the surface of the vast amounts of associated water reservoir as well as injected in the reservoir to maintain pressure.

of 'green' chemistry, are substances of natural origin and their various derivatives.

the selection and creation of appropriate reagents is often a nontrivial task.

**5.3 Scale inhibitors** 

As a result of flooding of the output at all stages of oil is the formation of salt deposits. Accumulating in the production strings on the surface of downhole pumping equipment and systems infield collection and preparation of oil, salt deposits not only cause great material costs in the process of removing them, but also to a significant loss in oil production.

The effectiveness of measures to combat the deposition of salt depends on an integrated approach to solving this problem. Need to know the physical and chemical processes and the causes of salt formation, taking into account the geological and physical conditions of occurrence of oil, human events and features of the development of oil and gas deposits and operating wells. The key areas for the deposition of salts from oil should be warning them, as a permanent measure, based on the best technological solutions that require scientific and methodological generalizations and systematic approach.

Based on the economic viability, depending on the conditions and characteristics of reservoir development, availability of raw materials, availability of technical resources and other factors may have different ways of dealing with this phenomenon, but in practice the problem of oil-field warning of salt deposits is decided mainly by inhibitor protection of wells and equipment .

Historically, the dominant classes of products inhibiting scaling in oil and gas production were phosphorous substances (eg aminomethylenephosphonates and phosphonic acids) and synthetic water soluble polymers such as polimaleates, polyacrylates, polisulfonates. Their main disadvantages are toxic to the environment and bioundegradability. The use of both classes of inhibitors are more tightly constrained as a result of legislative control. In recent years, the market introduced the latest "green" inhibitors: poly (amino acid) and chemically enhanced natural materials. This class of products has a low environmental toxicity, but the use of these inhibitors is still low because of the difficulty of their synthesis and significant economic costs compared with existing technologies.

Company AkzoNobel has been developed a new class of materials - hybrid polymers (copolymers of polysaccharides and polycarboxylic acids), (Figure 9) which combine the advantages of a single molecule, and synthetic and natural materials, the lack of benefit other than some of the restrictions currently known "green" products.

Fig. 9. AkzoNobel's hybrid polymers

New Green Oil-Field Agents 133

Microorganisms that cause biological corrosion, play a significant role in the corrosion of underground oil, gas and water pipelines, corrosion of ship and aircraft equipment, metallurgy and metalworking equipment, chemical and food industries. Microorganisms act as corrosive agents mainly due to the aggressive production of metabolites and a corrosive environment. As an aggressive advocate of metabolites of organic and inorganic acids,

In many cases, the microbiological contamination is obvious, with visible signs include changes in color medium viscosity, presence of slime, sludge and other sediments. Less obvious indicators - the inefficiency of film-forming corrosion inhibitors and the presence of

In the oil industry, the main agents of the corrosion process of metal fracture are sulfatereducing bacteria. They account for at least 90% of hydrogen sulfide entering the cycle of sulfur compounds that about 80% of all corrosion damage land and 50% damage of underground equipment. The economic costs of biological damage can be up to 3% of the

Spectrum inhibitors, bactericides and fungicides used to suppress the activity of microorganisms is extremely varied, but among them are many toxicants not only to microorganisms but also to warm-blooded. For example found that benzotriazole is used as

Among the aldehydes used in the manufacture of disinfectants found formaldehyde, glutaric and orthophthalic aldehydes having a broad spectrum of activity (Gram-positive and Gram-negative bacteria, fungi, mycobacteria, shell / implant failure viruses), including spores. Drugs, having in its composition glutaraldehyde get better, biocidal properties do not cause corrosion of materials of tools will not damage fabrics and surfaces are stable (which allows multiple solutions), have good penetration, fast destructible in wastewater. In fact, disinfectants on the basis of glutaraldehyde has been and remains the "gold standard" in many spheres of human activity. We can say that among the classes of oilfield chemicals

Reagents complex action can perform several functions simultaneously, for example, act as a corrosion inhibitor and scale inhibitor. In this case, it is not a simple mixture of several substances, and about a component that performs both functions. As often occurs in oil fields, several adverse events (corrode equipment, salt deposition, the presence of sulfatereducing bacteria, etc.), the creation of such reagents can significantly reduce the costs of

An example of a complex of the reagent is a corrosion inhibitor and scaling based on aspartic acid, proposed by Nalco. Synthesis is proposed to conduct a phase 2

a bactericide has high toxicity to mammals, and some arthropods.

**5.4 Biocides** 

enzymes, and hydrogen sulfide.

metal structures are exploited.

biocides are the most "green" reagents.

**5.5 New types of oilfield chemicals 5.5.1 Reagents complex action** 

minimizing damage.

(Figure 11).

contaminants such as salts or iron oxides.

Upon receipt of target compounds can be used a wide range of synthetic monomers, and the polysaccharide framework gives different functional characteristics while preserving the key properties of inhibitors. Studies conducted by the company revealed additional benefits of hybrid polymers, such as biodegradable and nontoxic. In addition, they are more environmentally sustainable solutions for the inhibition of salt deposition than synthetic products and not accumulated by living organisms.


Table 1. Biodegradability test results

These hybrid polymers are produced by more than 50% of renewable raw materials, as opposed to synthetic materials, and have lower emissions of carbon dioxide - hybridization reduces CO2 emissions by more than 50%.

The company also points to the adaptability of the technology of synthesis of target compounds, which expands the possibilities for optimizing the properties of the products according to specified criteria.

The company Rhodia offers to use as an inhibitor of salt deposits (carbonates and sulfates of magnesium, calcium and barium) natural polysaccharide composed of mannose and galactose residues in the native form and after modification of the relevant reagents (Figure 10). It is noteworthy that such products are not only patented, and commercially available.

Fig. 10. Rhodia's polymeric scale inhibitors

It is also noted that in the future as raw material for production may be other polysaccharides: starch and cellulose.

## **5.4 Biocides**

132 Green Chemistry – Environmentally Benign Approaches

Upon receipt of target compounds can be used a wide range of synthetic monomers, and the polysaccharide framework gives different functional characteristics while preserving the key properties of inhibitors. Studies conducted by the company revealed additional benefits of hybrid polymers, such as biodegradable and nontoxic. In addition, they are more environmentally sustainable solutions for the inhibition of salt deposition than synthetic

**Test (GLP standard) Method Result Goal Bioaccumulation** OECD 107 lgPow-2.95 lgPow<2.95 **Acute toxicity - algae** ISO 10253 EC50 >100 mg/l EC50 >100 mg/l **Acute toxicity - halibut fry** OECD 203 LC50 >100 mg/l LC50 >100 mg/l

These hybrid polymers are produced by more than 50% of renewable raw materials, as opposed to synthetic materials, and have lower emissions of carbon dioxide - hybridization

The company also points to the adaptability of the technology of synthesis of target compounds, which expands the possibilities for optimizing the properties of the products

The company Rhodia offers to use as an inhibitor of salt deposits (carbonates and sulfates of magnesium, calcium and barium) natural polysaccharide composed of mannose and galactose residues in the native form and after modification of the relevant reagents (Figure 10). It is noteworthy that such products are not only patented, and commercially available.

It is also noted that in the future as raw material for production may be other

TC147/SC5/WG2 LC50 >100 mg/l LC50 >100 mg/l

products and not accumulated by living organisms.

**Acute toxicity -** *acartia tonsa* ISO

Table 1. Biodegradability test results

according to specified criteria.

reduces CO2 emissions by more than 50%.

Fig. 10. Rhodia's polymeric scale inhibitors

polysaccharides: starch and cellulose.

Microorganisms that cause biological corrosion, play a significant role in the corrosion of underground oil, gas and water pipelines, corrosion of ship and aircraft equipment, metallurgy and metalworking equipment, chemical and food industries. Microorganisms act as corrosive agents mainly due to the aggressive production of metabolites and a corrosive environment. As an aggressive advocate of metabolites of organic and inorganic acids, enzymes, and hydrogen sulfide.

In many cases, the microbiological contamination is obvious, with visible signs include changes in color medium viscosity, presence of slime, sludge and other sediments. Less obvious indicators - the inefficiency of film-forming corrosion inhibitors and the presence of contaminants such as salts or iron oxides.

In the oil industry, the main agents of the corrosion process of metal fracture are sulfatereducing bacteria. They account for at least 90% of hydrogen sulfide entering the cycle of sulfur compounds that about 80% of all corrosion damage land and 50% damage of underground equipment. The economic costs of biological damage can be up to 3% of the metal structures are exploited.

Spectrum inhibitors, bactericides and fungicides used to suppress the activity of microorganisms is extremely varied, but among them are many toxicants not only to microorganisms but also to warm-blooded. For example found that benzotriazole is used as a bactericide has high toxicity to mammals, and some arthropods.

Among the aldehydes used in the manufacture of disinfectants found formaldehyde, glutaric and orthophthalic aldehydes having a broad spectrum of activity (Gram-positive and Gram-negative bacteria, fungi, mycobacteria, shell / implant failure viruses), including spores. Drugs, having in its composition glutaraldehyde get better, biocidal properties do not cause corrosion of materials of tools will not damage fabrics and surfaces are stable (which allows multiple solutions), have good penetration, fast destructible in wastewater. In fact, disinfectants on the basis of glutaraldehyde has been and remains the "gold standard" in many spheres of human activity. We can say that among the classes of oilfield chemicals biocides are the most "green" reagents.

## **5.5 New types of oilfield chemicals**

## **5.5.1 Reagents complex action**

Reagents complex action can perform several functions simultaneously, for example, act as a corrosion inhibitor and scale inhibitor. In this case, it is not a simple mixture of several substances, and about a component that performs both functions. As often occurs in oil fields, several adverse events (corrode equipment, salt deposition, the presence of sulfatereducing bacteria, etc.), the creation of such reagents can significantly reduce the costs of minimizing damage.

An example of a complex of the reagent is a corrosion inhibitor and scaling based on aspartic acid, proposed by Nalco. Synthesis is proposed to conduct a phase 2 (Figure 11).

New Green Oil-Field Agents 135

Distribution is the method of periodic filing solution in annulus, but it is not efficient, since the low dynamic poles reagent quickly carried away by fluid flow. In the most favorable

The method of dispensing reagents applied for maintenance of underground equipment and pipe elevator, but when there are problems in the bottomhole formation zone is necessary to supply into the reservoir. Dosing of reagent into the well (the system) is considered a reliable method, although it requires constant monitoring and maintenance of metering

Disadvantage of the periodic injection of the solution in the annulus is that the process is accompanied by illuviation of reagent into the rock. A common shortcoming of these

The use of submersible containers dispensers - the most economical and efficient way compared to others. The operating principle of these containers is based on different processes: dissolution, or leakage to the gravitational turbulent mixing of the reagent with the formation fluid. Submerged containers deliver reagent deep wells, where a minimal amount of active ingredient. However, the rate of dosing is determined by the downhole conditions, so the design of submerged container should be selected individually for each well. Usually this is not done or can not do so while the container is often different from the statements to the same dosing containers require special arrangements for their installation

It is now one of the most promising directions is the creation of microscopic containers,

the possibility of long-acting agents required, as a consequence of the increase

the possibility of joint use of substances of different classes that can react with each

more simple equipment needed to handle well, the lower price, due to better control

Microencapsulated product is a reagent, a prisoner in the polymer capsule. The reagent is pumped into the annulus, after which the capsules are deposited on the face. When operating the wells polymer membrane is dissolved, mixed with a liquid reservoir,

Within 1-2 days after the product is well increased yield of reagent and then the system comes into equilibrium and its removal is lower (but above the minimum inhibitory

reducing the duration of the reagent in the wells with high flow rates of fluids:

conditions of high dynamic frequency of feeding poles inhibitor is 15-20 days.

methods is too high consumption of reagent due to inefficiency of its use.

pumps and devices.

and maintenance.

interservice interval;

other for direct use;

hoppers, the so-called microencapsulation reagent.

 a longer residual effect of chemical treatment; a safer treatment with chemical agents;

The disadvantages of using such technology products are:

tendency to adsorb on the capsule surface solids;

and less consumption of reagents;

providing a way out of the reagent.

concentration) and permanent.

The advantages of using microencapsulated chemicals include:

Fig. 11. Synthesis of the reagent complex action

Highlights not only the protective properties, and biodegradability of these products with polymeric structure.

#### **5.5.2 Encapsulated reagents**

Along with the creation of new reagents for oil production, become important technological methods of their use. Depending on the reagents can be used for the following technologies:


Consistently can be used combined methods of delivery reagent, for example, initially periodic injection, and then - after 2-6 months - a continuous or periodic supply dosage of reagent in annulus.

Highlights not only the protective properties, and biodegradability of these products with

Along with the creation of new reagents for oil production, become important technological methods of their use. Depending on the reagents can be used for the

 periodic injection of a solution into the well followed by his supply in bottomhole zone. Consistently can be used combined methods of delivery reagent, for example, initially periodic injection, and then - after 2-6 months - a continuous or periodic supply dosage of

by continuous or periodic supply to the system using metering devices;

Fig. 11. Synthesis of the reagent complex action

polymeric structure.

following technologies:

reagent in annulus.

**5.5.2 Encapsulated reagents** 

Distribution is the method of periodic filing solution in annulus, but it is not efficient, since the low dynamic poles reagent quickly carried away by fluid flow. In the most favorable conditions of high dynamic frequency of feeding poles inhibitor is 15-20 days.

The method of dispensing reagents applied for maintenance of underground equipment and pipe elevator, but when there are problems in the bottomhole formation zone is necessary to supply into the reservoir. Dosing of reagent into the well (the system) is considered a reliable method, although it requires constant monitoring and maintenance of metering pumps and devices.

Disadvantage of the periodic injection of the solution in the annulus is that the process is accompanied by illuviation of reagent into the rock. A common shortcoming of these methods is too high consumption of reagent due to inefficiency of its use.

The use of submersible containers dispensers - the most economical and efficient way compared to others. The operating principle of these containers is based on different processes: dissolution, or leakage to the gravitational turbulent mixing of the reagent with the formation fluid. Submerged containers deliver reagent deep wells, where a minimal amount of active ingredient. However, the rate of dosing is determined by the downhole conditions, so the design of submerged container should be selected individually for each well. Usually this is not done or can not do so while the container is often different from the statements to the same dosing containers require special arrangements for their installation and maintenance.

It is now one of the most promising directions is the creation of microscopic containers, hoppers, the so-called microencapsulation reagent.

The advantages of using microencapsulated chemicals include:


The disadvantages of using such technology products are:


Microencapsulated product is a reagent, a prisoner in the polymer capsule. The reagent is pumped into the annulus, after which the capsules are deposited on the face. When operating the wells polymer membrane is dissolved, mixed with a liquid reservoir, providing a way out of the reagent.

Within 1-2 days after the product is well increased yield of reagent and then the system comes into equilibrium and its removal is lower (but above the minimum inhibitory concentration) and permanent.

New Green Oil-Field Agents 137




In recent years, clearly observed trends of developed countries identified the use of products "green chemistry" on the basis not only for reasons of environmental safety, development of similar products and technological schemes involves minimal risk to humans and nature, a more rational approach to the concept of obtaining a product, which ultimately account may lead to a significant reduction in price. Of course, this ideal case, but the examples in the modern chemical industry there that points to the undoubted promise of modern science and technology for "green" way, and it's not just a fad and a means of promoting new products, and a new stage of development of chemical

Authors would like to acknowledge to top managers of GC «Mirrico»: Malyhin I. and

Anastas, P. & Warner, J. (1998). *Green Chemistry: Theory and Practice*, Oxford University

Ash, M. & Ash, I. (2004). *Handbook of preservatives*, Synapse Information Resources, ISBN-10

Lunin, V., Tundo, P. & Lokteva, E. (2005). *Green Chemistry in Russia*, Poligrafica Venezia,

Sastri, V. (1998) *Corrosion inhibitors: principles and applications*, Willey, ISBN 0-471- 7608, New

Schramm, L. (2000) *Surfactants: fundamentals and applications in the petroleum industry*,

Karsa, D., & Ashworth, R. (2002). *Industrial biocides: selection and application*, Royal Society of

Scott, E., & Gorman, S. (2001). *Glutaraldehyde. Disinfection, sterilization and preservation*, ,

Cambridge University Press, ISBN 0-521-64067-9 Cambridge.

Lippincott Williams&Wilkins, ISBN 1-4051-0199-7, New-York.

Chemistry, ISBN 0-854-04805-7, Cambridge

Becker, J.( 1998). *Corrosion and scale handbook*, PennWell Books, ISBN 0878147497, Tulsa Durkee, J. (2006). *Management of industrial cleaning technology and processes*, Elsevier, ISBN-10

environmental safety, high effectiveness and cost of the desired product.

biological hazards.

involve significant economic costs.

technology, industry and science.

1890595667, Endicolt

0080448887 Oxford

York

ISBN 5-211-05001-0, Venezia

Press, ISBN 0-198-50234-6, New York

**7. Acknowledgment** 

Ramazanov R.

**8. References** 

Exit the reagent is carried out by the concentration gradient. With increasing consumption of reagent in the external environment is intensifying its removal from the capsule, and vice versa when - flow of reagent bounces back - his removal from the capsule slows down.

Material for the microcapsules are hydrophilic colloidal materials:


Fig. 12. Composition of the capsule

Encapsulated reagents offer oilfield companies such as Champion Technologies and Mirrico.

## **6. Conclusion**

Thus, we can formulate the basic requirements for the product oil and gas industry in line with the standards of "green chemistry":


However, the development and introduction of such products can be traced obvious difficulties.

Exit the reagent is carried out by the concentration gradient. With increasing consumption of reagent in the external environment is intensifying its removal from the capsule, and vice versa when - flow of reagent bounces back - his removal from the capsule slows


Encapsulated reagents offer oilfield companies such as Champion Technologies and Mirrico.

Thus, we can formulate the basic requirements for the product oil and gas industry in line

However, the development and introduction of such products can be traced obvious


Material for the microcapsules are hydrophilic colloidal materials:

as formaldehyde or glutaraldehyde (Figure 12).


Fig. 12. Composition of the capsule

with the standards of "green chemistry":

**6. Conclusion** 



difficulties.


down.


In recent years, clearly observed trends of developed countries identified the use of products "green chemistry" on the basis not only for reasons of environmental safety, development of similar products and technological schemes involves minimal risk to humans and nature, a more rational approach to the concept of obtaining a product, which ultimately account may lead to a significant reduction in price. Of course, this ideal case, but the examples in the modern chemical industry there that points to the undoubted promise of modern science and technology for "green" way, and it's not just a fad and a means of promoting new products, and a new stage of development of chemical technology, industry and science.

## **7. Acknowledgment**

Authors would like to acknowledge to top managers of GC «Mirrico»: Malyhin I. and Ramazanov R.

## **8. References**


**8** 

*México* 

Nora Elizondo et al.\*

**Green Synthesis and Characterizations** 

Metallic nanoparticles (nps) are of great interest because of the modification of properties observed due to size effects, modifying the catalytic, electronic, and optical properties of the

In the last years, biosynthesis of nps have been received considerable attention due to the growing need to develop clean, nontoxic chemicals, environmentally benign solvents and renewable materials [Gericke and Pinches, 2006; Harris and Bali, 2008]. As a result, researchers in the field of nanoparticle synthesis and assembly have turned towards the utilization of biological system such as yeast, fungi, bacteria and plant extracts for the synthesis of biocompatible metal and semiconductor nps through control nucleation and

The green method employing plant extracts have drawn attention as a simple and viable alternative to chemical procedures and physical methods, which consist of a low concentration of gold or silver precursor that is added to plant extract in solution to make up a final solution and centrifuged. The supernatant is heated at 50°C to 95°C. A change in the color of solution is observed during the heating process. Bioreduction of silver ions to yield metal nanoparticles using living plants, geranium leaf [Shankar et al., 2003], Neem leaf [Shankar et al., 2004a]. Very recently, they have demonstrated synthesis of gold nanotriangles and silver nps using *Aloevera* plant extracts [Chandran et al., 2006], *Emblica officinalis* (amla, Indian Gooseberry).[Amkamwar et al., 2005] Most of the above research on the synthesis of silver or gold nps utilizing plant extracts employed broths resulting from boiling fresh plant leaves. The green synthesis of silver nps using *Capsicum annuum* leaf extract has been reported.[Li et al., 2007] According to previous reports, the polyol components and the water-soluble heterocyclic components are mainly responsible for the

monometallic nps.[Bronstein et al., 2000; Chushak & Bartell, 2003; Tomas, 2003]

growth of inorganic nps [Kasthuri et al., 2009; Lee et al., 2011; Shankar et al., 2003].

 Paulina Segovia1,3, Víctor Coello3, Jesús Arriaga1, Sergio Belmares1, Aracelia Alcorta1, Francisco Hernández1, Ricardo Obregón1, Ernesto Torres2 and Francisco Paraguay4

*Universidad Autónoma de Nuevo León, San Nicolás de los Garza, N. L., México*

4 *CIMAV, Chihuahua, Complejo Ind. Chih., Chihuahua, Chih., México*

<sup>1</sup>*Facultad de Ciencias Físico-Matemáticas, México* 

<sup>3</sup>*CICESE, Monterrey,* PIIT, Apodaca, N. L., *México*

<sup>2</sup>*Facultad de Medicina, México*

**1. Introduction** 

 \*

**of Silver and Gold Nanoparticles** 

*Facultad de Ciencias Físico-Matemáticas, N. L., CP 66451,* 


## **Green Synthesis and Characterizations of Silver and Gold Nanoparticles**

Nora Elizondo et al.\* *Facultad de Ciencias Físico-Matemáticas, N. L., CP 66451, México* 

## **1. Introduction**

138 Green Chemistry – Environmentally Benign Approaches

Cook, S. (1999). Green chemistry – evolution or revolution?. *Green Chemistry*, Oct. 1999,

Karabinos, J. & Ballum, A. (1954). tall oil studies. II. Decolorization of polyethenoxy

tallates with ozone and hydrogen peroxide *J. Am. Oil Chem. Soc.*, Vol. 31 No 2,

G138-G140.

February 1954, pp. 71-74.

Metallic nanoparticles (nps) are of great interest because of the modification of properties observed due to size effects, modifying the catalytic, electronic, and optical properties of the monometallic nps.[Bronstein et al., 2000; Chushak & Bartell, 2003; Tomas, 2003]

In the last years, biosynthesis of nps have been received considerable attention due to the growing need to develop clean, nontoxic chemicals, environmentally benign solvents and renewable materials [Gericke and Pinches, 2006; Harris and Bali, 2008]. As a result, researchers in the field of nanoparticle synthesis and assembly have turned towards the utilization of biological system such as yeast, fungi, bacteria and plant extracts for the synthesis of biocompatible metal and semiconductor nps through control nucleation and growth of inorganic nps [Kasthuri et al., 2009; Lee et al., 2011; Shankar et al., 2003].

The green method employing plant extracts have drawn attention as a simple and viable alternative to chemical procedures and physical methods, which consist of a low concentration of gold or silver precursor that is added to plant extract in solution to make up a final solution and centrifuged. The supernatant is heated at 50°C to 95°C. A change in the color of solution is observed during the heating process. Bioreduction of silver ions to yield metal nanoparticles using living plants, geranium leaf [Shankar et al., 2003], Neem leaf [Shankar et al., 2004a]. Very recently, they have demonstrated synthesis of gold nanotriangles and silver nps using *Aloevera* plant extracts [Chandran et al., 2006], *Emblica officinalis* (amla, Indian Gooseberry).[Amkamwar et al., 2005] Most of the above research on the synthesis of silver or gold nps utilizing plant extracts employed broths resulting from boiling fresh plant leaves. The green synthesis of silver nps using *Capsicum annuum* leaf extract has been reported.[Li et al., 2007] According to previous reports, the polyol components and the water-soluble heterocyclic components are mainly responsible for the

Francisco Hernández1, Ricardo Obregón1, Ernesto Torres2 and Francisco Paraguay4

<sup>\*</sup> Paulina Segovia1,3, Víctor Coello3, Jesús Arriaga1, Sergio Belmares1, Aracelia Alcorta1,

<sup>1</sup>*Facultad de Ciencias Físico-Matemáticas, México* 

<sup>2</sup>*Facultad de Medicina, México*

*Universidad Autónoma de Nuevo León, San Nicolás de los Garza, N. L., México* <sup>3</sup>*CICESE, Monterrey,* PIIT, Apodaca, N. L., *México*

<sup>4</sup> *CIMAV, Chihuahua, Complejo Ind. Chih., Chihuahua, Chih., México*

Green Synthesis and Characterizations of Silver and Gold Nanoparticles 141

technique. There, we made use of chemical compounds of plants like *Rosa Berberifolia* and *Geranium Maculatum* in order to obtain ascorbic acid and polyphenols as reductor agents. Ascorbic acid (C6H8O6) and polyphenols like hydroxyphenol compounds are abundant components of plants. Ascorbic acid reaches a concentration of over 20 milimols in chloroplasts and occurs in all cell compartments including the cell wall. Additionally the acid has functions in photosynthesis as an enzyme cofactor (including synthesis of ethylene, gibberellins and anthocyanins) and in the control of cell growth. [Altansukha, 2010; Smirnoff & Wheeler, 2000] In nature, polyphenol is one of the most important chemicals in many reductive biological reactions widely found in plants and animals. The hydroxyphenol compounds and their derivatives could be used as versatile reducing agents for facile onepot synthesis of gold and silver nanoparticles with diverse morphological characters. Most of the reports on the biological synthesis of metal nps utilizing plant extracts employed broths obtained from boiled fresh plant leaves. In this present study, we report on the synthesis of silver and gold nps using *Aloe Barbadensis* and *Cucurbita Digitata* extracts at 60°C. The approach is a simple, cost-effective, stable for long time, reproducible and previously unexploited method excellent for nanofabrication. These plants are predominant species in America especially in Mexico. In the case of *Aloe Barbadensis* it has been used for medical applications such as there is some preliminary evidence that *Aloe Vera* extracts may be useful in the treatment of wound and burn healing, minor skin infections, sebaceous cysts, diabetes, and elevated blood lipids in humans(from Wikipedia).[Harris & Bali 2008] These positive effects are thought to be due to the presence of compounds such as polysaccharides, mannans, anthraquinones, and lectins.[Boudreau & Beland 2006; Eshun &

We use for the synthesizes plants like *Aloe Barbadensis* and *cactus plants like Cucurbita Digitata* that is a reminder plant in Mexico, also with compounds that have surfactant properties like saponins. Here, we show that green method reduces the temperature requirement which is in contrast to the obtained with the polyol method. The use of these natural components

The polyol method was followed to obtain nps passivated with poly(vinylpyrrolidone) (PVP). Hydrogen tetrachloroaurate (HAuCl4) (III) hydrate (99.99%), silver nitrate (AgNO3) (99.99%), and poly (N-vinyl-2-pyrrolidone) (PVP-K30, MW = 40000) were purchased from Sigma Aldrich, and 1, 2-ethylenediol (99.95%) was purchased from Fischer Chemicals; all the materials were used without any further purification. A 0.4 g sample of Poly (N-vinyl-2 pyrrolidone) (PVP) was dissolved in 50 mL of 1,2-ethylenediol (EG) under vigorous stirring, heating in reflux, until the desired temperature was reached (working temperatures ranged from 140°C to 190°C in increments of 10°C). For the monometallic nps, a 0.1 mM aqueous solution of the metal precursor was added to the EG-PVP solution, with continuous

The green method is an ecological synthesis technique. There, we made use of chemical compounds of plants like *Rosa Berberifolia*, *Geranium Maculatum, Aloe Barbadensis* and *Cucurbita Digitata* in order to obtain ascorbic acid as reductor agent from the extracts of these plants as can be seen from figure 2. Ascorbic acid (C6H8O6) is an abundant component of plants, which reaches a concentration of over 20 milimols in chloroplasts and occurs in all

He 2004; King et al., 1995; Vogler & Ernst 1999]

allows synthesize gold and silver nps.

**2. Experimental section** 

agitation for 3 h in reflux.

reduction of silver ions and the stabilization of the nps, respectively[Arangasamy & Munusamy, 2008; Nagajyoti et al., 2011].

Specific synthesis of nps and nanostructured materials are attracting attention in recent research because of their valuable properties which make them useful for catalysis, [El-Sayed & Narayanan, 2004] sensor technology, [Gomez-Romero, 2001] biological labeling, [Shankar et al., 2003] optoelectronics recording media and optics.[Qiu et al. 2004] The size, shape and surface morphology play pivotal roles in controlling the physical, chemical, optical and electronic properties of these nanoscopic materials.[Gracias et al., 2002; Kamat, 2002 ] This is particularly important for noble metals such as Au and Ag which have strong surface plasmon resonance (SPR) oscillations. The shape-selective metal nps such as rods, tubes, wires, triangles, prisms, hexagons and cubes can be regularly synthesized by chemical, biological and physical methods. [El-Sayet, 2001; Lim et al., 2008]

Many colloidal methods of synthesis have been approached to obtain metallic nps for this purpose, such as homogeneous reduction in aqueous solutions,[Shankar et al., 2004b]or phase transfer reactions,[Liz-Marzan & Philipse, 1995] with sodium citrate, hydrazine, NaBH4, and lithium triethylborohydride (LiBEt3H) as reducing agents, each of them yielding products with different physicochemical and structural characteristics.[Han et al., 1998] Among these, the polyol method has been reported to produce small nps as the final product, easily changing composition and surface modifiers. This technique does not require an additional reducing agent since the solvent by itself reduces the metallic species. However, besides the stoichiometry and order of addition of reagents in the synthesis process, one of the most important parameters in the preparation is the temperature. Modifications in temperature influence the reaction by changing the stabilization of the nps formed and the surface modifiers, e.g., PVP, and the nucleation rate of the reduced metallic atoms.[Schmid, 1994]

Gold (Au) and silver (Ag) nps have a diversity of interesting properties between which they emphasize the electrical ones, optical, catalytic and the applications in biomedicine like antibacterial and antiviral, same that depend on their morphology and size.

Characterization of these systems has been a difficult process where researchers have employed indirect measurements to identify the localization of the elements within the nps. A novel approach to study this kind of particles is based on the use of a high angle annular dark field (HAADF) technique, in a transmission electron microscope (TEM), which allows the observation of the elements due to atomic number, densities, or the presence of strain fields due to differences in lattice parameters, structure, the presence of surfactants or any other surface modifier besides the size of the particle and also by near-field scanning optical microscopy (NSOM) we determine the size of the particles.[Henglein, 2000; Turkevich et al., 1951]

The nps were synthesized using polyol and green methods. We made a comparison of these methods in order to investigate the influence of reaction parameters on the resulting particle size and its distribution. In the first method we use polyol process with poly (vinylpyrrolidone) (PVP) acting as a stabilizer and ethylenglycol as a reductor.[ Cao, 2004; Park et al., 2008] Such procedure yield different morphologies of metal nps (including gold and silver). [Burda et al., 2005; Gonzalez et al., 2009; Kasthuri et al., 2009; Rosi & Mirkin, 2005; Safaepour et al., 2009; Xia & Halas, 2005] The green method is an ecological synthesis

reduction of silver ions and the stabilization of the nps, respectively[Arangasamy &

Specific synthesis of nps and nanostructured materials are attracting attention in recent research because of their valuable properties which make them useful for catalysis, [El-Sayed & Narayanan, 2004] sensor technology, [Gomez-Romero, 2001] biological labeling, [Shankar et al., 2003] optoelectronics recording media and optics.[Qiu et al. 2004] The size, shape and surface morphology play pivotal roles in controlling the physical, chemical, optical and electronic properties of these nanoscopic materials.[Gracias et al., 2002; Kamat, 2002 ] This is particularly important for noble metals such as Au and Ag which have strong surface plasmon resonance (SPR) oscillations. The shape-selective metal nps such as rods, tubes, wires, triangles, prisms, hexagons and cubes can be regularly synthesized by

Many colloidal methods of synthesis have been approached to obtain metallic nps for this purpose, such as homogeneous reduction in aqueous solutions,[Shankar et al., 2004b]or phase transfer reactions,[Liz-Marzan & Philipse, 1995] with sodium citrate, hydrazine, NaBH4, and lithium triethylborohydride (LiBEt3H) as reducing agents, each of them yielding products with different physicochemical and structural characteristics.[Han et al., 1998] Among these, the polyol method has been reported to produce small nps as the final product, easily changing composition and surface modifiers. This technique does not require an additional reducing agent since the solvent by itself reduces the metallic species. However, besides the stoichiometry and order of addition of reagents in the synthesis process, one of the most important parameters in the preparation is the temperature. Modifications in temperature influence the reaction by changing the stabilization of the nps formed and the surface modifiers, e.g., PVP, and the nucleation rate of the reduced metallic

Gold (Au) and silver (Ag) nps have a diversity of interesting properties between which they emphasize the electrical ones, optical, catalytic and the applications in biomedicine like

Characterization of these systems has been a difficult process where researchers have employed indirect measurements to identify the localization of the elements within the nps. A novel approach to study this kind of particles is based on the use of a high angle annular dark field (HAADF) technique, in a transmission electron microscope (TEM), which allows the observation of the elements due to atomic number, densities, or the presence of strain fields due to differences in lattice parameters, structure, the presence of surfactants or any other surface modifier besides the size of the particle and also by near-field scanning optical microscopy (NSOM) we determine the size of the particles.[Henglein, 2000; Turkevich

The nps were synthesized using polyol and green methods. We made a comparison of these methods in order to investigate the influence of reaction parameters on the resulting particle size and its distribution. In the first method we use polyol process with poly (vinylpyrrolidone) (PVP) acting as a stabilizer and ethylenglycol as a reductor.[ Cao, 2004; Park et al., 2008] Such procedure yield different morphologies of metal nps (including gold and silver). [Burda et al., 2005; Gonzalez et al., 2009; Kasthuri et al., 2009; Rosi & Mirkin, 2005; Safaepour et al., 2009; Xia & Halas, 2005] The green method is an ecological synthesis

antibacterial and antiviral, same that depend on their morphology and size.

chemical, biological and physical methods. [El-Sayet, 2001; Lim et al., 2008]

Munusamy, 2008; Nagajyoti et al., 2011].

atoms.[Schmid, 1994]

et al., 1951]

technique. There, we made use of chemical compounds of plants like *Rosa Berberifolia* and *Geranium Maculatum* in order to obtain ascorbic acid and polyphenols as reductor agents. Ascorbic acid (C6H8O6) and polyphenols like hydroxyphenol compounds are abundant components of plants. Ascorbic acid reaches a concentration of over 20 milimols in chloroplasts and occurs in all cell compartments including the cell wall. Additionally the acid has functions in photosynthesis as an enzyme cofactor (including synthesis of ethylene, gibberellins and anthocyanins) and in the control of cell growth. [Altansukha, 2010; Smirnoff & Wheeler, 2000] In nature, polyphenol is one of the most important chemicals in many reductive biological reactions widely found in plants and animals. The hydroxyphenol compounds and their derivatives could be used as versatile reducing agents for facile onepot synthesis of gold and silver nanoparticles with diverse morphological characters. Most of the reports on the biological synthesis of metal nps utilizing plant extracts employed broths obtained from boiled fresh plant leaves. In this present study, we report on the synthesis of silver and gold nps using *Aloe Barbadensis* and *Cucurbita Digitata* extracts at 60°C. The approach is a simple, cost-effective, stable for long time, reproducible and previously unexploited method excellent for nanofabrication. These plants are predominant species in America especially in Mexico. In the case of *Aloe Barbadensis* it has been used for medical applications such as there is some preliminary evidence that *Aloe Vera* extracts may be useful in the treatment of wound and burn healing, minor skin infections, sebaceous cysts, diabetes, and elevated blood lipids in humans(from Wikipedia).[Harris & Bali 2008] These positive effects are thought to be due to the presence of compounds such as polysaccharides, mannans, anthraquinones, and lectins.[Boudreau & Beland 2006; Eshun & He 2004; King et al., 1995; Vogler & Ernst 1999]

We use for the synthesizes plants like *Aloe Barbadensis* and *cactus plants like Cucurbita Digitata* that is a reminder plant in Mexico, also with compounds that have surfactant properties like saponins. Here, we show that green method reduces the temperature requirement which is in contrast to the obtained with the polyol method. The use of these natural components allows synthesize gold and silver nps.

## **2. Experimental section**

The polyol method was followed to obtain nps passivated with poly(vinylpyrrolidone) (PVP). Hydrogen tetrachloroaurate (HAuCl4) (III) hydrate (99.99%), silver nitrate (AgNO3) (99.99%), and poly (N-vinyl-2-pyrrolidone) (PVP-K30, MW = 40000) were purchased from Sigma Aldrich, and 1, 2-ethylenediol (99.95%) was purchased from Fischer Chemicals; all the materials were used without any further purification. A 0.4 g sample of Poly (N-vinyl-2 pyrrolidone) (PVP) was dissolved in 50 mL of 1,2-ethylenediol (EG) under vigorous stirring, heating in reflux, until the desired temperature was reached (working temperatures ranged from 140°C to 190°C in increments of 10°C). For the monometallic nps, a 0.1 mM aqueous solution of the metal precursor was added to the EG-PVP solution, with continuous agitation for 3 h in reflux.

The green method is an ecological synthesis technique. There, we made use of chemical compounds of plants like *Rosa Berberifolia*, *Geranium Maculatum, Aloe Barbadensis* and *Cucurbita Digitata* in order to obtain ascorbic acid as reductor agent from the extracts of these plants as can be seen from figure 2. Ascorbic acid (C6H8O6) is an abundant component of plants, which reaches a concentration of over 20 milimols in chloroplasts and occurs in all

Green Synthesis and Characterizations of Silver and Gold Nanoparticles 143

Fig. 3. Photography of monometallic colloidal dispersions of gold nanoparticles in the solutions with the extracts of *Aloe Barbadensis*, the change of color is characteristic of gold and a function of the physical properties of metallic nanoparticles obtained by green

path length quartz cuvette in a Cary 5000 equipment.

This reaction describes the reduction of Au+ to Au0.

**3. Results and discussion** 

the temperature of reaction.

For the electron microscopy analysis of the metallic nps, samples were prepared over carbon coated copper TEM grids. HAADF and HRTEM images were taken with a JEOL 2010F and a FEI TITAN microscopes in the STEM mode, with the use of a HAADF detector with collection angles from 50 mrad to 110 mrad. Also by near-field scanning optical microscopy (NSOM) we determine the size of the particles. UV-vis spectra were obtained using a 10 mm

It is well known that the morphology and size distribution of metallic particles produced by the reduction of metallic salts in solution depends on various reaction conditions such as temperature, time, concentration, molar ratio of metallic salt/reducing agent, mode and order of addition of reagents, presence and type of protective agents, degree and type of agitation, and whether nucleation is homogeneous or heterogeneous [Sanguesa et al., 1992]. Following the polyol method with ethylene glycol as solvent reductor, it was possible to obtain monometallic nanoparticles with narrow size distributions in systems and different structures depending on the temperature of reaction. The monometallic synthesis of nanoparticles by itself showed distinctive morphologies of the nanoparticles depending on

Reaction proceeds in general as an oxidation of the ethylene glycol reducing the metallic

OH-CH2-CH2-OH → CH3-CHO + H2O (1)

6(CH3-CHO) + 2HAuCl4 → 3(CH3-CO-CO-CH3) + 2Au0 + 8HCl (2)

OH-CH2-CH2-OH → CH3-CHO + H2O (3)

2(CH3-CHO) + AgNO3 → (CH3-CO-CO-CH3) + Ag0 + HNO3 (4)

precursor to its zero-valence state. [Carotenuto et al. 2000; Sun et al., 2002]

method.

cell compartments including the cell wall. We use for the synthesizes also cactus extracts with compounds that have surfactant properties like saponins.

Fig. 1. The synthesizes by the green chemistry method were realized using extracts of plants with scientific names of: (a) *Rosa Berberiforia*, (b) *Geranium Maculatum,* (c) *Aloe Barbadensis*  and (d) *Cucúrbita Digitata.*(Images of this figure are from http://www. Google.com and http://www.Wikipedia.org)

Fig. 2. Reflux system used for the synthesis of silver and gold nanoparticles by polyol and green chemistry methods.

The extracts were prepared as of 1 to 40 grams of the mentioned fresh plants. They were heated in a flask with deionized water at 100°C under stirring for 10 minutes and filtered three times. Then from 10 to 50 milliliters of the extracts of these plants respectively were dissolved in water or in ethanol under vigorous stirring, heating in reflux, until the desired temperature was reached. For the gold and silver nps, a 0.1 mM aqueous solution of the metal precursor was added to the solutions with extracts, with continuous agitation for 30 minutes to 24 h in reflux like by the polyol method as can be seen in figure 2, in a working temperatures range from 60°C to 100°C. When the precursors were added to the reaction solutions, we observed drastic changes of the color of the solutions after one minute of the reaction time from yellow to dark brown in the case of silver nps and for gold nps synthesis the color of the solutions changed from yellow-pink tones to dark brown as shown in figure 3.

The synthesis of colloidal metallic nps was carried out taking into account the optimization of the conditions of nucleation and growth. For this reason, the variation of parameters like the concentration of the metallic precursors, reductor agent, amount of stabilizer, temperature and time of synthesis were realized.

Fig. 3. Photography of monometallic colloidal dispersions of gold nanoparticles in the solutions with the extracts of *Aloe Barbadensis*, the change of color is characteristic of gold and a function of the physical properties of metallic nanoparticles obtained by green method.

For the electron microscopy analysis of the metallic nps, samples were prepared over carbon coated copper TEM grids. HAADF and HRTEM images were taken with a JEOL 2010F and a FEI TITAN microscopes in the STEM mode, with the use of a HAADF detector with collection angles from 50 mrad to 110 mrad. Also by near-field scanning optical microscopy (NSOM) we determine the size of the particles. UV-vis spectra were obtained using a 10 mm path length quartz cuvette in a Cary 5000 equipment.

## **3. Results and discussion**

142 Green Chemistry – Environmentally Benign Approaches

cell compartments including the cell wall. We use for the synthesizes also cactus extracts

 a) b) c) d) Fig. 1. The synthesizes by the green chemistry method were realized using extracts of plants with scientific names of: (a) *Rosa Berberiforia*, (b) *Geranium Maculatum,* (c) *Aloe Barbadensis*  and (d) *Cucúrbita Digitata.*(Images of this figure are from http://www. Google.com and

Fig. 2. Reflux system used for the synthesis of silver and gold nanoparticles by polyol and

The extracts were prepared as of 1 to 40 grams of the mentioned fresh plants. They were heated in a flask with deionized water at 100°C under stirring for 10 minutes and filtered three times. Then from 10 to 50 milliliters of the extracts of these plants respectively were dissolved in water or in ethanol under vigorous stirring, heating in reflux, until the desired temperature was reached. For the gold and silver nps, a 0.1 mM aqueous solution of the metal precursor was added to the solutions with extracts, with continuous agitation for 30 minutes to 24 h in reflux like by the polyol method as can be seen in figure 2, in a working temperatures range from 60°C to 100°C. When the precursors were added to the reaction solutions, we observed drastic changes of the color of the solutions after one minute of the reaction time from yellow to dark brown in the case of silver nps and for gold nps synthesis the color of the solutions

The synthesis of colloidal metallic nps was carried out taking into account the optimization of the conditions of nucleation and growth. For this reason, the variation of parameters like the concentration of the metallic precursors, reductor agent, amount of stabilizer,

changed from yellow-pink tones to dark brown as shown in figure 3.

temperature and time of synthesis were realized.

with compounds that have surfactant properties like saponins.

http://www.Wikipedia.org)

green chemistry methods.

It is well known that the morphology and size distribution of metallic particles produced by the reduction of metallic salts in solution depends on various reaction conditions such as temperature, time, concentration, molar ratio of metallic salt/reducing agent, mode and order of addition of reagents, presence and type of protective agents, degree and type of agitation, and whether nucleation is homogeneous or heterogeneous [Sanguesa et al., 1992].

Following the polyol method with ethylene glycol as solvent reductor, it was possible to obtain monometallic nanoparticles with narrow size distributions in systems and different structures depending on the temperature of reaction. The monometallic synthesis of nanoparticles by itself showed distinctive morphologies of the nanoparticles depending on the temperature of reaction.

Reaction proceeds in general as an oxidation of the ethylene glycol reducing the metallic precursor to its zero-valence state. [Carotenuto et al. 2000; Sun et al., 2002]

$$\text{OH-CH}\_{2}\text{-CH}\_{2}\text{-OH} \rightarrow \text{CH}\_{3}\text{-CHO} + \text{H}\_{2}\text{O} \tag{1}$$

$$\text{\(CH\_3\text{-CHO}\)} + \text{\text{2HAuCl}\_4} \rightarrow \text{\(CH\_3\text{-CO-CO-CH}\_3\text{)} + \text{2Au}\text{\(\text{\(}2\)}\)}\tag{2}$$

This reaction describes the reduction of Au+ to Au0.

$$\text{OH-CH}\_{2}\text{-CH}\_{2}\text{OH} \rightarrow \text{CH}\_{3}\text{-CHO} + \text{H}\_{2}\text{O} \tag{3}$$

$$\text{2(CH-CHO)} + \text{AgNO}\_3 \rightarrow \text{(CH-CO-CO-CH}\_3\text{)} + \text{Ag}^0 + \text{HNO}\_3\tag{4}$$

Green Synthesis and Characterizations of Silver and Gold Nanoparticles 145

truncated triangles, and decahedrons. Also rods with diameters between 50 and 150 nm and a few micrometers in length were observed. All of these structures had very well-defined shapes. The final product was a clear solution with large Au precipitates, some of them visible to the bare eye. At 140°C more rounded particles were observed, with shapes less defined. These particles were also smaller than in the 100°C case, approximately from 300 nm to 500 nm in sizes. At this temperature the structures observed tend to be more spherical than in the previous case. The final product at this temperature also was a clear solution with an evident precipitation of Au at the bottom of the flask. Finally, at 190°C the particles observed were smaller than in the last two cases mentioned from 200 nm to 250 nm in approximate sizes. At this temperature we can observe again particles with more geometric shapes than the ones observed at 140°C, as we can notice in Figure 5 a and b. Some rods with less than 100 nm in diameter and less than 1 *μ*m in length were observed. The final product at this temperature had a purple color with an observable precipitation of Au at the

The reaction scheme for producing fine and monodisperse metallic nanoparticles using the polyol process involves the following successive reactions: reduction of the soluble silver nitrate and tetrachloroauric acid by ethylene glycol, nucleation of metallic silver and gold, and growth of individual nuclei in the presence of a protective agent, PVP. The fully reacted particle sizes synthesized from the polyol process depended strongly on the ramping rate of the precursor solutions to the reaction temperature; at a lower heating rate larger particles were generated, most likely due to a slower nucleation rate, while at a higher rate faster nucleation produced smaller-sized particles. At a heating rate of 2°C min−1, the mean size of silver particles was 50 nm, and increasing the heating rate to 10°C min−1 yielded smaller and more monodisperse particles with a mean size of 25 nm as can be seen in figure 5c. The particle size of the silver decreased slightly when the reaction temperature was decreased

In order to obtain monodisperse metal particles, generally, rapid nucleation in a short period of time is important; that is, almost all ionic species have to be reduced rapidly to metallic species simultaneously, followed by conversion to stable nuclei so as to be grown [Dongjo, Kim et al., 2006]. In the method of heating a precursor solution, however, both nucleation and growth can proceed gradually with increasing temperature. As such, it is

Therefore, the rapid injection of silver nitrate aqueous solution into ethylene glycol maintained at the reaction temperature would guarantee a short burst of nucleation after which the nuclei would continue to grow without additional nucleation, thus ensuring

Upon addition of the silver nitrate and tetrachloroauric acid aqueous solutions to hot ethylene glycol, the Ag+ and Au+ species are reduced to metallic silver and gold

The concentrations of metallic silver and gold in solution increase, reaching the supersaturation conditions and finally the critical concentration to nucleate. Spontaneous nucleation then takes place very rapidly and many nuclei are formed in a short time, lowering the silver and gold concentrations below the nucleation and supersaturation levels into the saturation concentration region. After a short period of nucleation, the nuclei grow

difficult to synthesize particles with high monodispersity.

bottom of the flask.

from 150°C to 100°C.

monodispersity.

nanoparticles.

This reaction describes the reduction of Ag+ to Ag0.

In the presence of a surface modifier, the reaction changes depending on the ability of the metal to coordinate with it, as in the case of PVP where the metallic precursor could coordinate with the oxygen of the pyrrolidone group, when the particles are in the nanometer size range, while when they are in the micrometer size range the coordination is mainly with the nitrogen, as reported by Bonet et al. [Bonet et al., 2000; Sun et al., 2002] as can be observed in figure 4.

Fig. 4. A proposed mechanism of interactions between PVP and metal ions when the formed particles are in the nanometer size range.

The interaction between metal precursor and PVP has an effect on the formation of PVPstabilized metal colloidal nanoparticles. The interaction between metal colloids and PVP is an important factor to influence the stabilities and the sizes of PVP-stabilized colloidal nanoparticles and their physicochemical properties. The reaction time for the polyol method was around 3 hours and the nps were synthesized between 100°C and 190°C. The shape and size of gold nanoparticles differs greatly from one temperature of synthesis to the next one, observing a high polydispersity in all these Au systems. The growth behavior is modified when temperature changes, allowing the presence of one-dimensional structures, spheres and angular structures. At 100°C large particles were observed in approximate sizes from 0.2 *μ*m to 1 *μ*m in a variety of different well-defined geometric forms such as triangles,

In the presence of a surface modifier, the reaction changes depending on the ability of the metal to coordinate with it, as in the case of PVP where the metallic precursor could coordinate with the oxygen of the pyrrolidone group, when the particles are in the nanometer size range, while when they are in the micrometer size range the coordination is mainly with the nitrogen, as reported by Bonet et al. [Bonet et al., 2000; Sun et al., 2002] as

Fig. 4. A proposed mechanism of interactions between PVP and metal ions when the formed

The interaction between metal precursor and PVP has an effect on the formation of PVPstabilized metal colloidal nanoparticles. The interaction between metal colloids and PVP is an important factor to influence the stabilities and the sizes of PVP-stabilized colloidal nanoparticles and their physicochemical properties. The reaction time for the polyol method was around 3 hours and the nps were synthesized between 100°C and 190°C. The shape and size of gold nanoparticles differs greatly from one temperature of synthesis to the next one, observing a high polydispersity in all these Au systems. The growth behavior is modified when temperature changes, allowing the presence of one-dimensional structures, spheres and angular structures. At 100°C large particles were observed in approximate sizes from 0.2 *μ*m to 1 *μ*m in a variety of different well-defined geometric forms such as triangles,

This reaction describes the reduction of Ag+ to Ag0.

can be observed in figure 4.

particles are in the nanometer size range.

truncated triangles, and decahedrons. Also rods with diameters between 50 and 150 nm and a few micrometers in length were observed. All of these structures had very well-defined shapes. The final product was a clear solution with large Au precipitates, some of them visible to the bare eye. At 140°C more rounded particles were observed, with shapes less defined. These particles were also smaller than in the 100°C case, approximately from 300 nm to 500 nm in sizes. At this temperature the structures observed tend to be more spherical than in the previous case. The final product at this temperature also was a clear solution with an evident precipitation of Au at the bottom of the flask. Finally, at 190°C the particles observed were smaller than in the last two cases mentioned from 200 nm to 250 nm in approximate sizes. At this temperature we can observe again particles with more geometric shapes than the ones observed at 140°C, as we can notice in Figure 5 a and b. Some rods with less than 100 nm in diameter and less than 1 *μ*m in length were observed. The final product at this temperature had a purple color with an observable precipitation of Au at the bottom of the flask.

The reaction scheme for producing fine and monodisperse metallic nanoparticles using the polyol process involves the following successive reactions: reduction of the soluble silver nitrate and tetrachloroauric acid by ethylene glycol, nucleation of metallic silver and gold, and growth of individual nuclei in the presence of a protective agent, PVP. The fully reacted particle sizes synthesized from the polyol process depended strongly on the ramping rate of the precursor solutions to the reaction temperature; at a lower heating rate larger particles were generated, most likely due to a slower nucleation rate, while at a higher rate faster nucleation produced smaller-sized particles. At a heating rate of 2°C min−1, the mean size of silver particles was 50 nm, and increasing the heating rate to 10°C min−1 yielded smaller and more monodisperse particles with a mean size of 25 nm as can be seen in figure 5c. The particle size of the silver decreased slightly when the reaction temperature was decreased from 150°C to 100°C.

In order to obtain monodisperse metal particles, generally, rapid nucleation in a short period of time is important; that is, almost all ionic species have to be reduced rapidly to metallic species simultaneously, followed by conversion to stable nuclei so as to be grown [Dongjo, Kim et al., 2006]. In the method of heating a precursor solution, however, both nucleation and growth can proceed gradually with increasing temperature. As such, it is difficult to synthesize particles with high monodispersity.

Therefore, the rapid injection of silver nitrate aqueous solution into ethylene glycol maintained at the reaction temperature would guarantee a short burst of nucleation after which the nuclei would continue to grow without additional nucleation, thus ensuring monodispersity.

Upon addition of the silver nitrate and tetrachloroauric acid aqueous solutions to hot ethylene glycol, the Ag+ and Au+ species are reduced to metallic silver and gold nanoparticles.

The concentrations of metallic silver and gold in solution increase, reaching the supersaturation conditions and finally the critical concentration to nucleate. Spontaneous nucleation then takes place very rapidly and many nuclei are formed in a short time, lowering the silver and gold concentrations below the nucleation and supersaturation levels into the saturation concentration region. After a short period of nucleation, the nuclei grow

Green Synthesis and Characterizations of Silver and Gold Nanoparticles 147

From this study it was found that by the polyol method the temperature plays a decisive role in the synthesis of gold and silver nanoparticles protected with PVP. It does not only affect the rates of reduction and nucleation of the metals, but it also affects the coordination between the metals and the polymeric protective agent, the distribution of elements in the

In the green method the reaction time is reduced from 3 hours to 30 minutes until 1 hour at 60°C, but we carried out the reaction during 24 hours in order to observe the growth of the

a) b) c)

Fig. 5. TEM images of gold nanoparticles synthesized at 190 °C (a) 200 nm in size and (b) 250

The TEM characterization reveal the formation of nps of these metals, independent of the employed method, with a size distribution between 20 and 120 nm for gold (see figure 5)

The NSOM showed that the size of gold nps synthesized was of 25 nm with very narrow

Plants contain a complex network of antioxidant metabolites and enzymes that work together to prevent oxidative damage to cellular components. Isolated quercetin [Wu, 2008] and polysaccharides [Ahmad et al, 2009; Collera et al., 2005; Vedpriya, 2010; Jagadeesh et al., 2004] have been used for the synthesis of silver and gold nanoparticles. Plants Extracts like *Aloe Barbadensis* is reported to contain chemically different groups of compounds: polyphenols, flavonoids, sterols, triterpenes, triterpenoid saponins, beta-phenylethylamines, tetrahydroisoquinolines, reducing sugars like glucose and fructose, and proteins, in all

The plant extract is reported to have activities of scavenging superoxide anion radicals and 1, 1-diphenyl-2-picrylhydrazyl radicals (DPPH). It could be that these water-soluble scavenging superoxide anion radicals and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radicals present in the plant extract be responsible for the reduction of silver and synthesis of nanoparticles through biogenic routes. The exact mechanism of the formation of these

nm in size and silver nanoparticles synthesized at 120°C (c) by the polyol method.

nanoparticles, and the final particle size.

and between 10 and 27 nm for the silver.

distribution.

extracts.

particles.

by the deposition of metallic silver and gold until the system reaches the saturation concentration. At the end of the growth period, all the metal nanoparticles have grown at almost the same rate and the systems exhibit a narrow particle size distribution.

This temperature dependence on particle size can be explained as follows. Because of the relatively high temperature used in the synthesis of silver and gold nanoparticles by polyol method, the Brownian motion and mobility of surface atoms increase. This enhances the probability of particle collision, adhesion, and subsequent coalescence. However, PVP is added to protect the particles from agglomeration. Particle coalescence is the means by which the system tries to attain thermodynamic equilibrium by reducing its total surface area.

Spherical silver nanoparticles with a controllable size and high monodispersity were synthesized by the polyol method as can be seen from figure 5c. Two different synthesis methods for producing the Ag nanoparticles were compared in terms of particle size and monodispersity. Silver nanoparticles with a size of 25 ± 4 nm were obtained at a reaction temperature of 120°C and a heating rate of 10°C min−1 in the precursor heating method, where the heating rate was a critical parameter affecting particle size.

In the precursor injection method, on the other hand, the injection rate and reaction temperature were important factors for producing uniform-sized Ag with a reduced size. Silver nanoparitlces with a size of 18 ± 2 nm were obtained at an injection rate of 2*.*0 ml s−<sup>1</sup> and a reaction temperature of 100°C. The injection of the precursor solution into a hot solution is an effective means to induce rapid nucleation in a short period of time, ensuring the fabrication of silver and gold nanoparticles with a smaller size and a narrower size distribution by the polyol method.

The effect of temperature in the polyol method is crucial because at lower temperatures the oxidation potential of ethylene glycol is bigger than at higher temperatures. This means that at lower temperatures the oxidation of ethylene glycol is less favored, which traduces in fewer electrons available in the reaction environment to reduce the metals. As the temperature keeps increasing, the oxidation potential of the ethylene glycol decreases, indicating that this electrochemical reaction is favored at higher temperatures. This translates as an increment in the electrons concentration in the reaction environment. [Bonet et al., 1999]

In contrast, the reduction potential of the metals is not affected by the temperature, according to Bonet et al. It is insensitive to the reaction temperature, but there still is an effect on the reduction of the precursors related to the temperature dependence of the diffusion of metal species. Another effect of temperature on the reduction of the metal precursors is that the energy barrier that opposes to the reduction of the precursor is equal to the difference between the oxidation potential of the ethylene glycol and the reduction potential of the metal species. [Bonet et al., 1999]

Once the oxidation potential of the ethylene glycol is lowered down to the same value of the reduction potential of the metal precursor, the reduction of the metal precursor will occur spontaneously and followed by the nucleation of metal nanoparticles. [Bonet et al., 1999] From this analysis one can conclude that at higher temperatures the reduction of the metal species will be favored and also the oxidation of the ethylene glycol. This will decrease the time needed to reduce the metal precursor and the nucleation time needed to the formation of metal particles.

by the deposition of metallic silver and gold until the system reaches the saturation concentration. At the end of the growth period, all the metal nanoparticles have grown at

This temperature dependence on particle size can be explained as follows. Because of the relatively high temperature used in the synthesis of silver and gold nanoparticles by polyol method, the Brownian motion and mobility of surface atoms increase. This enhances the probability of particle collision, adhesion, and subsequent coalescence. However, PVP is added to protect the particles from agglomeration. Particle coalescence is the means by which

Spherical silver nanoparticles with a controllable size and high monodispersity were synthesized by the polyol method as can be seen from figure 5c. Two different synthesis methods for producing the Ag nanoparticles were compared in terms of particle size and monodispersity. Silver nanoparticles with a size of 25 ± 4 nm were obtained at a reaction temperature of 120°C and a heating rate of 10°C min−1 in the precursor heating method,

In the precursor injection method, on the other hand, the injection rate and reaction temperature were important factors for producing uniform-sized Ag with a reduced size. Silver nanoparitlces with a size of 18 ± 2 nm were obtained at an injection rate of 2*.*0 ml s−<sup>1</sup> and a reaction temperature of 100°C. The injection of the precursor solution into a hot solution is an effective means to induce rapid nucleation in a short period of time, ensuring the fabrication of silver and gold nanoparticles with a smaller size and a narrower size

The effect of temperature in the polyol method is crucial because at lower temperatures the oxidation potential of ethylene glycol is bigger than at higher temperatures. This means that at lower temperatures the oxidation of ethylene glycol is less favored, which traduces in fewer electrons available in the reaction environment to reduce the metals. As the temperature keeps increasing, the oxidation potential of the ethylene glycol decreases, indicating that this electrochemical reaction is favored at higher temperatures. This translates as an increment in the electrons concentration in the reaction environment. [Bonet

In contrast, the reduction potential of the metals is not affected by the temperature, according to Bonet et al. It is insensitive to the reaction temperature, but there still is an effect on the reduction of the precursors related to the temperature dependence of the diffusion of metal species. Another effect of temperature on the reduction of the metal precursors is that the energy barrier that opposes to the reduction of the precursor is equal to the difference between the oxidation potential of the ethylene glycol and the reduction

Once the oxidation potential of the ethylene glycol is lowered down to the same value of the reduction potential of the metal precursor, the reduction of the metal precursor will occur spontaneously and followed by the nucleation of metal nanoparticles. [Bonet et al., 1999] From this analysis one can conclude that at higher temperatures the reduction of the metal species will be favored and also the oxidation of the ethylene glycol. This will decrease the time needed to reduce the metal precursor and the nucleation time needed to the formation

almost the same rate and the systems exhibit a narrow particle size distribution.

the system tries to attain thermodynamic equilibrium by reducing its total surface area.

where the heating rate was a critical parameter affecting particle size.

distribution by the polyol method.

potential of the metal species. [Bonet et al., 1999]

et al., 1999]

of metal particles.

From this study it was found that by the polyol method the temperature plays a decisive role in the synthesis of gold and silver nanoparticles protected with PVP. It does not only affect the rates of reduction and nucleation of the metals, but it also affects the coordination between the metals and the polymeric protective agent, the distribution of elements in the nanoparticles, and the final particle size.

In the green method the reaction time is reduced from 3 hours to 30 minutes until 1 hour at 60°C, but we carried out the reaction during 24 hours in order to observe the growth of the particles.

Fig. 5. TEM images of gold nanoparticles synthesized at 190 °C (a) 200 nm in size and (b) 250 nm in size and silver nanoparticles synthesized at 120°C (c) by the polyol method.

The TEM characterization reveal the formation of nps of these metals, independent of the employed method, with a size distribution between 20 and 120 nm for gold (see figure 5) and between 10 and 27 nm for the silver.

The NSOM showed that the size of gold nps synthesized was of 25 nm with very narrow distribution.

Plants contain a complex network of antioxidant metabolites and enzymes that work together to prevent oxidative damage to cellular components. Isolated quercetin [Wu, 2008] and polysaccharides [Ahmad et al, 2009; Collera et al., 2005; Vedpriya, 2010; Jagadeesh et al., 2004] have been used for the synthesis of silver and gold nanoparticles. Plants Extracts like *Aloe Barbadensis* is reported to contain chemically different groups of compounds: polyphenols, flavonoids, sterols, triterpenes, triterpenoid saponins, beta-phenylethylamines, tetrahydroisoquinolines, reducing sugars like glucose and fructose, and proteins, in all extracts.

The plant extract is reported to have activities of scavenging superoxide anion radicals and 1, 1-diphenyl-2-picrylhydrazyl radicals (DPPH). It could be that these water-soluble scavenging superoxide anion radicals and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radicals present in the plant extract be responsible for the reduction of silver and synthesis of nanoparticles through biogenic routes. The exact mechanism of the formation of these

Green Synthesis and Characterizations of Silver and Gold Nanoparticles 149

respectively using extracts of plants, ascorbic acid and polyphenols as reducing agents obtained from *Geranium Maculatum* leaves and *Rosa Berberiforia* petals and like natural surfactants saponins and simultaneous reducing agents in some cases were used *Aloe* 

Scheme 1. Ascorbic acid reduction mechanism of gold and silver ions to obtain Ag0 and

a) b)

It is important to know the exact nature of the silver and gold nanoparticles formed, and this can be deduced from the XRD Spectrum of the Sample. XRD patterns of derived Ag nps from Figure 7(a) show four intense peaks in the whole spectrum of 2θ° values ranging from 20° to 90°. XRD spectra of pure crystalline silver structures have been published by the Joint Committee on Powder Diffraction Standards (file no. 04-0787). A comparison of our XRD spectrum with the Standard confirmed that the silver nanoparticles formed in our experiments were in the form of face centered cubic nanocrystals, as evidenced by the peaks

Fig. 6. UV-Visible absorption spectrum of the Au (1a) and Ag (1b) nps synthesized by

polyol and green chemistry respectively.

*Barbadensis* and cactus extracts from *Cucúrbita Digitata*.

Au0 nps.

nanoparticles in these biological media is unknown. Presumably, biosynthetic products or reduced cofactors play an important role in the reduction of respective salts to nanoparticles. However, it seems probable that some glucose and ascorbate reduce AgNO3 and HAuCl4 to form nanoparticles. [Ahmad et al. 2011; Hu et al., 2003]

The probability of reduction of AgNO3 to silver may be illustrated due to the mechanism known as glycolysis. Plants fix CO2 in presence of sunlight. Carbohydrates are the first cellular constituent formed by the photosynthesizing organism on absorption of light. This carbohydrate is utilized by the cell as glucose by Glycolysis. This is the metabolic pathway that converts glucose C6H12O6 into pyruvate and hydrogen ion:

$$\mathrm{CH\_3COCOO^- + H^+} \tag{5}$$

The free energy released in this process is used to form the high-energy compounds, ATP adenosine triphosphate and NADH (reduced nicotinamide adenine dinuleotide). Glycolysis can be represented by the following simple equation:

$$\text{Glucose} + 2\text{ADP} + 2\text{Pi} + 2\text{NAD}^\* = 2\text{ Pyruvate} + 2\text{ATP} + 2\text{NADH} + 2\text{H}^\* \tag{6}$$

Glycolysis is a definite sequence of ten reactions involving ten intermediate compounds [Ahmad et al. 2011]. Large amount of H+ ions are produced along with ATP. Nicotinamide adenine dinucleotide, abbreviated NAD+, is a coenzyme found in all living cells. NAD is a strong reducing agent. NAD+ is involved in redox reactions, carrying electrons from one reaction to another. The coenzyme is therefore found in two forms in cells. NAD+ is an oxidizing agent—it accepts electrons from other molecules and becomes reduced. This reaction forms NADH, which can donate electrons. These electron transfer reactions are the main function of NAD:

$$\mathrm{AgNO\_3^{-}} \rightarrow \mathrm{Ag^{+} + NO\_3^{-}} \quad \text{or} \quad 2\mathrm{HAuCl\_4} \rightarrow 2\mathrm{Au^{+} + 4HCl}$$

$$\mathrm{NAD^{+} + e^{-} \rightarrow NAD\_{i}}$$

$$\mathrm{NAD + H^{+} \rightarrow NADH + e^{-}}$$

$$\mathrm{e^{-} + Ag^{+} \rightarrow Ag^{0} \quad \text{or} \quad \mathrm{e^{-} + Au^{+} \rightarrow Au^{0}}}$$

NAD+ keeps on getting reoxidized and gets constantly regenerated due to redox reactions. This might have led to transformations of Ag or Au ions to Ag0 or Au0. Another mechanism for the reduction of Ag or Au ions to silver or gold could be due to the presence of watersoluble antioxidative substances like ascorbate. This acid is present at high levels in all parts of plants. Ascorbic acid is a reducing agent and can reduce, and thereby neutralize, reactive oxygen species leading to the formation of ascorbate radical and an electron.

This free electron reduces the Ag+ or Au+ ions to Ag0 or Au0 as can be seen in scheme 1.

In accordance with the studies of UV visible spectroscopy, whose plasmons are in figure 6 for Au and Ag synthesized nps the results shown an absorption energy in 547 nm and 415 nm respectively.

The use of these natural components allows synthesize metallic nps. In the green method, gold and silver nps were prepared by the same reduction of HAuCl4 and AgNO3

nanoparticles in these biological media is unknown. Presumably, biosynthetic products or reduced cofactors play an important role in the reduction of respective salts to nanoparticles. However, it seems probable that some glucose and ascorbate reduce AgNO3

The probability of reduction of AgNO3 to silver may be illustrated due to the mechanism known as glycolysis. Plants fix CO2 in presence of sunlight. Carbohydrates are the first cellular constituent formed by the photosynthesizing organism on absorption of light. This carbohydrate is utilized by the cell as glucose by Glycolysis. This is the metabolic pathway

 CH3COCOO*<sup>−</sup>* + H+ (5) The free energy released in this process is used to form the high-energy compounds, ATP adenosine triphosphate and NADH (reduced nicotinamide adenine dinuleotide). Glycolysis

 Glucose + 2ADP + 2Pi + 2NAD+ *=* 2 Pyruvate + 2ATP + 2 NADH + 2H+ (6) Glycolysis is a definite sequence of ten reactions involving ten intermediate compounds [Ahmad et al. 2011]. Large amount of H+ ions are produced along with ATP. Nicotinamide adenine dinucleotide, abbreviated NAD+, is a coenzyme found in all living cells. NAD is a strong reducing agent. NAD+ is involved in redox reactions, carrying electrons from one reaction to another. The coenzyme is therefore found in two forms in cells. NAD+ is an oxidizing agent—it accepts electrons from other molecules and becomes reduced. This reaction forms NADH, which can donate electrons. These electron transfer reactions are the

NAD+ + e*−→* NAD,

e*<sup>−</sup>* +Ag+ *→* Ag0 or e*<sup>−</sup>* +Au+ *→* Au0 NAD+ keeps on getting reoxidized and gets constantly regenerated due to redox reactions. This might have led to transformations of Ag or Au ions to Ag0 or Au0. Another mechanism for the reduction of Ag or Au ions to silver or gold could be due to the presence of watersoluble antioxidative substances like ascorbate. This acid is present at high levels in all parts of plants. Ascorbic acid is a reducing agent and can reduce, and thereby neutralize, reactive

This free electron reduces the Ag+ or Au+ ions to Ag0 or Au0 as can be seen in scheme 1.

In accordance with the studies of UV visible spectroscopy, whose plasmons are in figure 6 for Au and Ag synthesized nps the results shown an absorption energy in 547 nm and 415

The use of these natural components allows synthesize metallic nps. In the green method, gold and silver nps were prepared by the same reduction of HAuCl4 and AgNO3

oxygen species leading to the formation of ascorbate radical and an electron.

*<sup>−</sup>* or 2HAuCl4 → 2Au+ + 4HCl

NAD + H+ *→* NADH + e*−*, (7)

and HAuCl4 to form nanoparticles. [Ahmad et al. 2011; Hu et al., 2003]

that converts glucose C6H12O6 into pyruvate and hydrogen ion:

can be represented by the following simple equation:

AgNO3*→* Ag+ +NO3

main function of NAD:

nm respectively.

respectively using extracts of plants, ascorbic acid and polyphenols as reducing agents obtained from *Geranium Maculatum* leaves and *Rosa Berberiforia* petals and like natural surfactants saponins and simultaneous reducing agents in some cases were used *Aloe Barbadensis* and cactus extracts from *Cucúrbita Digitata*.

Scheme 1. Ascorbic acid reduction mechanism of gold and silver ions to obtain Ag0 and Au0 nps.

Fig. 6. UV-Visible absorption spectrum of the Au (1a) and Ag (1b) nps synthesized by polyol and green chemistry respectively.

It is important to know the exact nature of the silver and gold nanoparticles formed, and this can be deduced from the XRD Spectrum of the Sample. XRD patterns of derived Ag nps from Figure 7(a) show four intense peaks in the whole spectrum of 2θ° values ranging from 20° to 90°. XRD spectra of pure crystalline silver structures have been published by the Joint Committee on Powder Diffraction Standards (file no. 04-0787). A comparison of our XRD spectrum with the Standard confirmed that the silver nanoparticles formed in our experiments were in the form of face centered cubic nanocrystals, as evidenced by the peaks

Green Synthesis and Characterizations of Silver and Gold Nanoparticles 151

a) Image corresponding to Spectrum 1 and EDX for silver nanoparticles.

b) Image corresponding to Spectrum 34 and EDX bright field for gold nanoparticles.

a) b) c)

Fig. 9. Transmission electron microscopy images of Au nps at same magnification of (a) *Rosa* 

concentration of plants extracts approximately (0.002M) with HAuCl4 (1 X 10-3 M) at 1 hours

*Berberiforia*, (b) *Geranium Maculatum,* and (c) *Cucúrbita Digitata* using the same low

and 60°C.

Fig. 8. a) Image corresponding to select area 1 and Energy-Dispersive Absorption Spectroscopy photograph for silver nanoparticles, and b) Image corresponding to select area 34 and Energy-Dispersive Absorption Spectroscopy photograph for gold nanoparticles.

at 2θ values of 38.52°, 44.49°, 64.70°, and 77.63°, corresponding to [111], [200], [220], and [311] planes for silver, respectively. In the case of gold nanoparticles in the whole spectrum of 2θ° values ranging from 35° to 80°, four new reflection signals appear at ca. 38.10°, 44.40°, 64.87°, and 77.84° in the XRD pattern of the Au, corresponding to the [111], [200], [220] and [311] planes of the Au, respectively as can be seen in Figure 7 (b), indicating that crystal structure of the gold nanoparticles was face centered cubic(JCPDS 4-0783)in this case also.

Scherrer's equation for broadening resulting from a small crystalline size, the mean, effective, or apparent dimension of the crystal composing the powder is:

$$\text{Phkl} = k \lambda / \beta 1 / 2 \cos \theta \tag{8}$$

Fig. 7. X-ray diffractograms of silver (a) and gold (b) nanoparticles synthesized as of extracts of *Aloe Barbadensis* at 1 hour and 60°C.

where θ is the Bragg angle, *λ* is the wavelength of the X ray used, *β* is the breadth of the pure diffraction profile in radians on 2θ scale, and *k* is a constant approximately equal to unity and related both to the crystalline shape and to the way in which θ is defined. The best possible value of *k* has been estimated as 0.89. The Full Width at Half Maximum (FWHM) values measured for [111], [200], [220], and [311] planes of reflection were used with the Debye-Scherrer equation (8) to calculate the size of the nanoparticles. [Ahmad, N. et al. 2011] Moreover, the average size of the gold nanoparticles was also determined from the width of the reflection according to the Scherrer formula*.* The value of *D* calculated from the (111) reflection were *k* is 0.90 of the cubic phase of Au was ca. 25 nm, which is basically in agreement with the results of transmission electron microscopy (TEM) experiments for *Aloe Barbadensis* at 1 hour and 60°C.

Further analysis of the silver and gold nanoparticles by energy dispersive spectroscopy confirmed the presence of the signals characteristic of silver and gold respectively. Figure 8 shows the Energy-Dispersive Absorption Spectroscopy photographs of derived Ag nps and Au nps. All the peaks of Ag and Au respectively are observed and are assigned. Peaks for Cu and C are from the grid used, and the peaks for S, P, and Si (in the case of Au) correspond to the protein capping over the Ag nps and Au nps.

at 2θ values of 38.52°, 44.49°, 64.70°, and 77.63°, corresponding to [111], [200], [220], and [311] planes for silver, respectively. In the case of gold nanoparticles in the whole spectrum of 2θ° values ranging from 35° to 80°, four new reflection signals appear at ca. 38.10°, 44.40°, 64.87°, and 77.84° in the XRD pattern of the Au, corresponding to the [111], [200], [220] and [311] planes of the Au, respectively as can be seen in Figure 7 (b), indicating that crystal structure of the gold nanoparticles was face centered cubic(JCPDS 4-0783)in this case also. Scherrer's equation for broadening resulting from a small crystalline size, the mean,

Phkl *= kλ/β*1*/*2 cosθ (8)

 a) b) Fig. 7. X-ray diffractograms of silver (a) and gold (b) nanoparticles synthesized as of extracts

where θ is the Bragg angle, *λ* is the wavelength of the X ray used, *β* is the breadth of the pure diffraction profile in radians on 2θ scale, and *k* is a constant approximately equal to unity and related both to the crystalline shape and to the way in which θ is defined. The best possible value of *k* has been estimated as 0.89. The Full Width at Half Maximum (FWHM) values measured for [111], [200], [220], and [311] planes of reflection were used with the Debye-Scherrer equation (8) to calculate the size of the nanoparticles. [Ahmad, N. et al. 2011] Moreover, the average size of the gold nanoparticles was also determined from the width of the reflection according to the Scherrer formula*.* The value of *D* calculated from the (111) reflection were *k* is 0.90 of the cubic phase of Au was ca. 25 nm, which is basically in agreement with the results of transmission electron microscopy (TEM) experiments for *Aloe* 

Further analysis of the silver and gold nanoparticles by energy dispersive spectroscopy confirmed the presence of the signals characteristic of silver and gold respectively. Figure 8 shows the Energy-Dispersive Absorption Spectroscopy photographs of derived Ag nps and Au nps. All the peaks of Ag and Au respectively are observed and are assigned. Peaks for Cu and C are from the grid used, and the peaks for S, P, and Si (in the case of Au)

correspond to the protein capping over the Ag nps and Au nps.

effective, or apparent dimension of the crystal composing the powder is:

of *Aloe Barbadensis* at 1 hour and 60°C.

*Barbadensis* at 1 hour and 60°C.

a) Image corresponding to Spectrum 1 and EDX for silver nanoparticles.

b) Image corresponding to Spectrum 34 and EDX bright field for gold nanoparticles.

Fig. 8. a) Image corresponding to select area 1 and Energy-Dispersive Absorption Spectroscopy photograph for silver nanoparticles, and b) Image corresponding to select area 34 and Energy-Dispersive Absorption Spectroscopy photograph for gold nanoparticles.

Fig. 9. Transmission electron microscopy images of Au nps at same magnification of (a) *Rosa Berberiforia*, (b) *Geranium Maculatum,* and (c) *Cucúrbita Digitata* using the same low concentration of plants extracts approximately (0.002M) with HAuCl4 (1 X 10-3 M) at 1 hours and 60°C.

Green Synthesis and Characterizations of Silver and Gold Nanoparticles 153

figure 12c a gold nanoparticle of 4nm in size, synthesized with extracts of *Cucúrbita Digitata* at high concentration of plant extract of 0.003M. The gold nps synthesized with extracts of *Aloe Barbadensis* were used to prepare nanoarrays for the study of optical plasmonic

a) b) c)

concentration of plant extract of 0.0015 M approximately of *Aloe Barbadensis* with AgNO3 (1

a) b) c)

The anisotropic gold and spherical–quasi-spherical silver nps were synthesized by reducing aqueous chloroauric acid (HAuCl4) and silver nitrate (AgNO3) solution with the extract of *Aloe Barbadensis* at 60°C temperature. The size and shape of the nps can be controlled by

Fig. 12. High resolution transmission electron microscopy images of (a) gold nps synthesized with extracts of *Aloe Barbadensis* at 1 hour and 60°C using a concentration of plant extract of 0.0025 M approximately with a size distribution of 25 nm approximately, (b) a gold nanoparticle synthesized with extracts of *Cucúrbita Digitata* using a concentration of plant extract of 0.0018M approximately with a size of 150 nm and (c) a gold nanoparticle synthesized with extracts of *Cucúrbita Digitata* with a size of 4 nm at 60°C using a high

Fig. 11. Transmission electron microscopy images of Ag nps at different magnifications of (a) High Resolution -TEM image at a concentration of plant extract of 0.004 M, (b) High-

TEM image at a concentration of plant extract of 0.002 M, (c) HAADF image at a

phenomena in another work. [Coello et al., 2010]

X 10-3 M) at 1 hours and 60°C.

concentration of plant extract of 0.003M.

varying the concentration of plants extracts like *Aloe Barbadensis.*

d) Rod shape. e) Hexagonal shape. f) Cubic shape.

Fig. 10. Images of gold nanoparticles observed with different shapes synthesized as of *Aloe Barbadensis* extracts at different conditions varying the concentration of the extract from 0.0015 to 0.004 M, using: high resolution TEM: a) Quasi-spherical, b) Triangle, c) Rhombohedral shapes; HAADark Field TEM image: d) Rod shape; and Bright field TEM images: e) hexagonal shape and f) cubic shape gold nanoparticles.

In the figures 9 and 10, it is possible to identify large population of polydispersed gold nps synthesized as of *Rosa Berberiforia* petals, *Geranium Maculatum* leads*, Cucúrbita Digitata* cactus at same reaction conditions, and *Aloe Barbadensis* varying the concentration of plant extracts from 0.0015 to 0.004M, the consisted of spherical-, quasi-spherical-, ellipsoidal-, triangular-, hexagonal-, rombohedral-, trapezhoidal- and rod-shaped with irregular contours.

The morphology of the Ag nps was predominantly spherical and quasi-spherical as shown in figure 11, and they appear to be monodisperse for *Aloe Barbadensis* with AgNO3 (1 X 10-3 M) at 1 hours and 60°C at different concentration of plant extract. Some of the nps were found to be oval and/or elliptical at high concentration of plant extract. Such variation in shape and size of nanoparticles synthesized by biological systems is common.

The figure 12. shows high resolution transmission electron micrographs of gold nps, synthesized with extracts of *Aloe Barbadensis* at 1 hour and 60°C using a concentration of plant extract of 0.0025 M approximately with an average size distribution of 25nm (figure 12a), the figure 12b shows a gold nanoparticle of 150 nm in size, synthesized with extracts of *Cucúrbita Digitata* using a concentration of plant extract of 0.0018M approximately and

a) Quasi-spherical shape. b) Triangle shape. c) Rhombohedral shape.

d) Rod shape. e) Hexagonal shape. f) Cubic shape.

Fig. 10. Images of gold nanoparticles observed with different shapes synthesized as of *Aloe Barbadensis* extracts at different conditions varying the concentration of the extract from 0.0015 to 0.004 M, using: high resolution TEM: a) Quasi-spherical, b) Triangle, c)

Rhombohedral shapes; HAADark Field TEM image: d) Rod shape; and Bright field TEM

In the figures 9 and 10, it is possible to identify large population of polydispersed gold nps synthesized as of *Rosa Berberiforia* petals, *Geranium Maculatum* leads*, Cucúrbita Digitata* cactus at same reaction conditions, and *Aloe Barbadensis* varying the concentration of plant extracts from 0.0015 to 0.004M, the consisted of spherical-, quasi-spherical-, ellipsoidal-, triangular-, hexagonal-, rombohedral-, trapezhoidal- and rod-shaped with irregular

The morphology of the Ag nps was predominantly spherical and quasi-spherical as shown in figure 11, and they appear to be monodisperse for *Aloe Barbadensis* with AgNO3 (1 X 10-3 M) at 1 hours and 60°C at different concentration of plant extract. Some of the nps were found to be oval and/or elliptical at high concentration of plant extract. Such variation in

The figure 12. shows high resolution transmission electron micrographs of gold nps, synthesized with extracts of *Aloe Barbadensis* at 1 hour and 60°C using a concentration of plant extract of 0.0025 M approximately with an average size distribution of 25nm (figure 12a), the figure 12b shows a gold nanoparticle of 150 nm in size, synthesized with extracts of *Cucúrbita Digitata* using a concentration of plant extract of 0.0018M approximately and

shape and size of nanoparticles synthesized by biological systems is common.

images: e) hexagonal shape and f) cubic shape gold nanoparticles.

contours.

figure 12c a gold nanoparticle of 4nm in size, synthesized with extracts of *Cucúrbita Digitata* at high concentration of plant extract of 0.003M. The gold nps synthesized with extracts of *Aloe Barbadensis* were used to prepare nanoarrays for the study of optical plasmonic phenomena in another work. [Coello et al., 2010]

Fig. 11. Transmission electron microscopy images of Ag nps at different magnifications of (a) High Resolution -TEM image at a concentration of plant extract of 0.004 M, (b) High-TEM image at a concentration of plant extract of 0.002 M, (c) HAADF image at a concentration of plant extract of 0.0015 M approximately of *Aloe Barbadensis* with AgNO3 (1 X 10-3 M) at 1 hours and 60°C.

Fig. 12. High resolution transmission electron microscopy images of (a) gold nps synthesized with extracts of *Aloe Barbadensis* at 1 hour and 60°C using a concentration of plant extract of 0.0025 M approximately with a size distribution of 25 nm approximately, (b) a gold nanoparticle synthesized with extracts of *Cucúrbita Digitata* using a concentration of plant extract of 0.0018M approximately with a size of 150 nm and (c) a gold nanoparticle synthesized with extracts of *Cucúrbita Digitata* with a size of 4 nm at 60°C using a high concentration of plant extract of 0.003M.

The anisotropic gold and spherical–quasi-spherical silver nps were synthesized by reducing aqueous chloroauric acid (HAuCl4) and silver nitrate (AgNO3) solution with the extract of *Aloe Barbadensis* at 60°C temperature. The size and shape of the nps can be controlled by varying the concentration of plants extracts like *Aloe Barbadensis.*

Green Synthesis and Characterizations of Silver and Gold Nanoparticles 155

preparation and the temperature, Au and Ag crystallizes in different shapes and sizes to form spherical in the case of Ag, prisms, and hexagonal structures in the case of Au. Sizes vary from the nanometer to micrometer scale level depending on the plant extract used for preparation. Synthesized Au and Ag nanostructures were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and UV spectroscopy.

In this original work, we show that green method reduces the temperature requirement, which is in contrast to the obtained with the polyol method. In the green method the size and shape of the nps can be controlled by varying the concentration of plant extracts and the reaction time. The use of these natural components allows synthesize metallic nps with very

Authors would like to acknowledge to Facultad de Ciencias Físico Matemáticas and Microscopy Laboratory of CIIDIT de la Universidad Autónoma de Nuevo León, to

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narrow distribution.

**6. References** 

**5. Acknowledgment** 

The case of low concentration of extract with HAuCl4 offers the aid of electron-donating group containing extract leads to formation of hexagonal-or triangular-shaped gold nps. Transmission electron microscopy (TEM) analysis revealed that the shape changes on the gold nps from hexagonal to spherical particles with increasing initial concentration of *Aloe Barbadensis*.

The electron-donating methoxy (–OCH3) groups containing *Aloe Barbadensis* can provide a suitable environment for the formation of nps. A bioreductive approach of anisotropic gold and silver nps utilizing the *Aloe Barbadensis* has been demonstrated which provides a simple and efficient way for the synthesis of nanomaterials with tunable optical properties directed by particle shape.

The presence of small amount of *Aloe Barbadensis* leads to slow reduction of HAuCl4 ions which facilitated the formation of triangular- or hexagonal-shaped nps. Whereas greater amount of *Aloe Barbadensis* leads to higher population of spherical nps and was confirmed from the UV–visible and TEM analysis. The electron-donating nature of –OCH3 group of the *Aloe Barbadensis* plays a leading role for the formation and stabilization of nps, respectively results in accordance with Kasthuri et al.[Kasthuri, et al., 2009] as shown in scheme 2.

Scheme 2. The presence of small amount of *Aloe Barbadensis* leads to slow reduction of HAuCl4 ions which facilitated the formation of triangular- or hexagonal-shaped nps. Whereas greater amount of *Aloe Barbadensis* leads to higher population of spherical nps and was confirmed from TEM analysis.

## **4. Conclusion**

One-step green synthesis of gold (Au) and silver (Ag) nanostructures is described using naturally occurring biodegradable plant-based surfactants, without any special reducing agent/capping agents. This green method uses water as a benign solvent and surfactant/plant extract as a reducing agent. Depending upon the Au and Ag concentration used for the preparation and the temperature, Au and Ag crystallizes in different shapes and sizes to form spherical in the case of Ag, prisms, and hexagonal structures in the case of Au. Sizes vary from the nanometer to micrometer scale level depending on the plant extract used for preparation. Synthesized Au and Ag nanostructures were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and UV spectroscopy.

In this original work, we show that green method reduces the temperature requirement, which is in contrast to the obtained with the polyol method. In the green method the size and shape of the nps can be controlled by varying the concentration of plant extracts and the reaction time. The use of these natural components allows synthesize metallic nps with very narrow distribution.

## **5. Acknowledgment**

Authors would like to acknowledge to Facultad de Ciencias Físico Matemáticas and Microscopy Laboratory of CIIDIT de la Universidad Autónoma de Nuevo León, to Nanotechnology Laboratory of CIMAV Chihuahua, México.

## **6. References**

154 Green Chemistry – Environmentally Benign Approaches

The case of low concentration of extract with HAuCl4 offers the aid of electron-donating group containing extract leads to formation of hexagonal-or triangular-shaped gold nps. Transmission electron microscopy (TEM) analysis revealed that the shape changes on the gold nps from hexagonal to spherical particles with increasing initial concentration of *Aloe* 

The electron-donating methoxy (–OCH3) groups containing *Aloe Barbadensis* can provide a suitable environment for the formation of nps. A bioreductive approach of anisotropic gold and silver nps utilizing the *Aloe Barbadensis* has been demonstrated which provides a simple and efficient way for the synthesis of nanomaterials with tunable optical properties directed

The presence of small amount of *Aloe Barbadensis* leads to slow reduction of HAuCl4 ions which facilitated the formation of triangular- or hexagonal-shaped nps. Whereas greater amount of *Aloe Barbadensis* leads to higher population of spherical nps and was confirmed from the UV–visible and TEM analysis. The electron-donating nature of –OCH3 group of the *Aloe Barbadensis* plays a leading role for the formation and stabilization of nps, respectively results in accordance with Kasthuri et al.[Kasthuri, et al., 2009] as shown in scheme 2.

Scheme 2. The presence of small amount of *Aloe Barbadensis* leads to slow reduction of HAuCl4 ions which facilitated the formation of triangular- or hexagonal-shaped nps.

Whereas greater amount of *Aloe Barbadensis* leads to higher population of spherical nps and

One-step green synthesis of gold (Au) and silver (Ag) nanostructures is described using naturally occurring biodegradable plant-based surfactants, without any special reducing agent/capping agents. This green method uses water as a benign solvent and surfactant/plant extract as a reducing agent. Depending upon the Au and Ag concentration used for the

*Barbadensis*.

by particle shape.

was confirmed from TEM analysis.

**4. Conclusion** 


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## *Edited by Mazaahir Kidwai and Neeraj Kumar Mishra*

Green chemistry is chemistry for the environment. It is really a philosophy and way of thinking that can help chemistry in research and production to develop more ecofriendly solutions. Green chemistry is considered an essential piece of a comprehensive program to protect human health and the environment. In its essence, green chemistry is a science-based non-regulatory and economically driven approach to achieving the goals of environmental protection and sustainable development. Combining the technological progress with environmental safety is one of the key challenges of the millennium. In this context, this book describes the environmentally benign approaches for the industries as well as chemical laboratories. In order to provide an insight into step change technologies, this book was edited by green organic chemists.

Photo by Jaroslav74 / iStock

Green Chemistry - Environmentally Benign Approaches

Green Chemistry

Environmentally Benign Approaches

*Edited by Mazaahir Kidwai* 

*and Neeraj Kumar Mishra*