**1. Introduction**

As can be inspected from the literature, there were rising concerns in the mid-1980s, regarding the plentiful of the waste being produced by the chemical industry [1, 2]. A paradigm change was undoubtedly desirable, from the old-fashioned perceptions of reaction selectivity, and efficiency which emphasis fundamentally on the chemical yields, to one that allocates the value to the enlargement of the bulk raw materials exploitation, avoidance of the utilization of the hazardous chemicals/ reagents/solvents and also preventation of the waste being formed within the

**6**

*Current Topics in Chirality - From Chemistry to Biology*

[1] Higashi T, Takeuchi T: Oyo Butsuri 1998; 67, 1142-1145. https://doi. org/10.11470/oubutsu1932.67.1142 and

[2] Michaeli K, Kantor-Uriel N, Naaman R, Waldeck DH, Chem. Soc. Rev. 2016; 45, 6478 – 6487. https://doi. org/10.1039/C6CS00369A and

references therein.

**References**

references therein.

boundaries of environmental awareness. To this context, in 1987, the term sustainable development was coined by Brundtland, in his report; he mainly focused on the emergence of the societal and industrial development to afford an escalating global population with a suitable value of life in such a way that it should be sustainable over a long period of time [3]. Therefore, complete balance necessities to be found among the three Ps-planet, people, profit i.e. environmental impact, societal equity and economic development. More specifically, in sharp contrast to the green chemistry, sustainable development also comprises an economic factor and if a technology is not economically viable, it could not be sustainable for a long time. Remarkably, a tremendous curiosity in sustainable and green progress, united with a cultivating concern for the climate change, has engrossed attention on resource competence and also driving the shift from a conventional linear flow of bulk materials in a "take−make−use−dispose"economy, towards the greener and even more sustainable globular economy. Interestingly, since the 12 principles of green chemistry (*Prevention of waste; Atom economy; Less hazardous chemical syntheses; Designing safer chemicals with fewer hazards; Safer solvents and auxiliaries; Design for energy efficiency; Use of renewable feedstocks; Reduce derivatives during synthesis; Catalysis; Design for degradation; Real-time analysis for pollution prevention; Inherently safer chemistry for accident prevention*), postulated by Anastas & Warner in 1998 [4], scientists around the world are trying to reduce the volatile organic solvents (VOCs) which generally are the major portion (approx. 80% of the total content) of the reaction vessel as compare to the reactants/reagents, and also has the tendency to escape into the environment, which in turns contribute to ozone depletion as well as smog in urban areas, and hence extremely dangerous for mankind [5]. Therefore, great efforts are being put forward to reduce these hazardous VOCs, and the corrosive acid catalysts, participating in the reaction to make the chemical processes even more sustainable and environmentally friendlier [6]. To this context, over the past few decades, several surrogates for instance water, ionic liquids, supercritical fluids, and switchable solvents in addition to many green strategies such as ultrasound, flow chemistry, biocatalysis, microwaves, and multi-component etc., have successfully been developed [7–9]. Generally, water is thought to be an archetype solvent as it enjoy many classical properties, nonetheless it not only suffer from insolubility issues with the majority of organic compounds but also has a difficulty of removing it after the completion of the reaction because of its high boiling point, and even in many cases compounds gets decompose into the water in addition, some reactions for example amidations and transesterifications, can not be performed in water because of competing product hydrolysis [10]. On the other hand, supercritical fluids which possess low vapor pressure along with the advantages of easy disposal/removal, and recycling, are thought to be the best eco-friendly substitutes of VOCs, but, they requires more sophisticated equipment to perform the reaction. To this context, researchers turn their attention towards the ionic liquids due to their remarkable physiochemical properties but owing to their high cost as well as involvement of the non-renewable resources besides purification before their usage make them of bit doubt from green perception [11]. Consequently, bearing in mind, the urgency of the suitable alternative green solvents in place of conventional solvents to carry out the crucial synthetic transformations for sustainable development in R and D and also for the chemical industry, Abbott's 2003 discovery of the deep eutectic solvents (DESs), also known as low transition temperature mixtures (LTTMs), or low-melting mixtures (LMMs) or deep eutectic ionic liquids (DEILs), has become one of the strongest pillars to the modern synthetic community. Generally, in DES, two/three components are mixed in an appropriate amount to generate a eutectic mixture with lower melting point as compare to the individual components being used [12–15]. As a consequence, an infinite number of melts involving different compositions/components with

**9**

**Figure 1.**

*Low Melting Mixture of L-(+)-Tartaric Acid and* N,N′*-Dimethyl Urea: A New Arrival...*

distinctive properties like price of the raw materials, melting point, polarity, dissolving ability etc., can be accomplished effortlessly. Interestingly, because of the involvement of non-covalent interactions including hydrogen bonds, it has been noticed that the melting points of the DESs are generally below 100°C, even some of them are liquid at room temperature, and they have been the role model among the greener solvents over the past two decades to both academic as well as industrial community because of their remarkable properties and benefits such as biodegradability, low cost and low vapor pressure in addition to non-toxicity and good thermal stability. Among the DESs, a low melting mixture of DMU/TA can be regarded as the solvent of the 21st century, as it hold the following features: (i) Generally, it does not require tedious work-up after the reaction is being completed, rather, just filtration after addition of the water to the reaction mixture while hot, furnishes the analytically pure compounds and most of the time no need of chromatographic purification but simple recrystallization provides the pure form of the required products; (ii) the melting mixture can willingly be recovered and recycled several times without any substantial loss in the activity; (iii) the reaction cleanly underwent towards the product formation at faster rate as compare to the known procedure, and mostly better yields are obtained under operationally simple reaction conditions; (iv) No additional catalyst and solvents are needed in this method, as in conventional procedure, generally both, the corrosive catalysts as well as hazardous, flammable, and volatile organic solvents are being employed; (v) No inert atmosphere is required for a reaction to be successfully completed in parallel yields; (vi) This method also provide good selectivity and also exhibit excellent functional group tolerance; (vii) Easy preparation of the melt from the bulk renewable resources and no further purification before its utilization is needed; (viii) improved safety and very simple

*DOI: http://dx.doi.org/10.5772/intechopen.97392*

handling as comparison to the conventional practices.

*12 principles of green chemistry and the achievements made in DMU/TA.*

Bearing all the above mentioned applications and peculiar physiochemical properties of the DMU/TA melt in mind, which we still feel is immature, although employed for a variety of successful reactions for instance Diels-Alder reaction,

*Low Melting Mixture of L-(+)-Tartaric Acid and* N,N′*-Dimethyl Urea: A New Arrival... DOI: http://dx.doi.org/10.5772/intechopen.97392*

distinctive properties like price of the raw materials, melting point, polarity, dissolving ability etc., can be accomplished effortlessly. Interestingly, because of the involvement of non-covalent interactions including hydrogen bonds, it has been noticed that the melting points of the DESs are generally below 100°C, even some of them are liquid at room temperature, and they have been the role model among the greener solvents over the past two decades to both academic as well as industrial community because of their remarkable properties and benefits such as biodegradability, low cost and low vapor pressure in addition to non-toxicity and good thermal stability. Among the DESs, a low melting mixture of DMU/TA can be regarded as the solvent of the 21st century, as it hold the following features: (i) Generally, it does not require tedious work-up after the reaction is being completed, rather, just filtration after addition of the water to the reaction mixture while hot, furnishes the analytically pure compounds and most of the time no need of chromatographic purification but simple recrystallization provides the pure form of the required products; (ii) the melting mixture can willingly be recovered and recycled several times without any substantial loss in the activity; (iii) the reaction cleanly underwent towards the product formation at faster rate as compare to the known procedure, and mostly better yields are obtained under operationally simple reaction conditions; (iv) No additional catalyst and solvents are needed in this method, as in conventional procedure, generally both, the corrosive catalysts as well as hazardous, flammable, and volatile organic solvents are being employed; (v) No inert atmosphere is required for a reaction to be successfully completed in parallel yields; (vi) This method also provide good selectivity and also exhibit excellent functional group tolerance; (vii) Easy preparation of the melt from the bulk renewable resources and no further purification before its utilization is needed; (viii) improved safety and very simple handling as comparison to the conventional practices.

Bearing all the above mentioned applications and peculiar physiochemical properties of the DMU/TA melt in mind, which we still feel is immature, although employed for a variety of successful reactions for instance Diels-Alder reaction,

*12 principles of green chemistry and the achievements made in DMU/TA.*

*Current Topics in Chirality - From Chemistry to Biology*

boundaries of environmental awareness. To this context, in 1987, the term sustainable development was coined by Brundtland, in his report; he mainly focused on the emergence of the societal and industrial development to afford an escalating global population with a suitable value of life in such a way that it should be sustainable over a long period of time [3]. Therefore, complete balance necessities to be found among the three Ps-planet, people, profit i.e. environmental impact, societal equity and economic development. More specifically, in sharp contrast to the green chemistry, sustainable development also comprises an economic factor and if a technology is not economically viable, it could not be sustainable for a long time. Remarkably, a tremendous curiosity in sustainable and green progress, united with a cultivating concern for the climate change, has engrossed attention on resource competence and also driving the shift from a conventional linear flow of bulk materials in a "take−make−use−dispose"economy, towards the greener and even more sustainable globular economy. Interestingly, since the 12 principles of green chemistry (*Prevention of waste; Atom economy; Less hazardous chemical syntheses; Designing safer chemicals with fewer hazards; Safer solvents and auxiliaries; Design for energy efficiency; Use of renewable feedstocks; Reduce derivatives during synthesis; Catalysis; Design for degradation; Real-time analysis for pollution prevention; Inherently safer chemistry for accident prevention*), postulated by Anastas & Warner in 1998 [4], scientists around the world are trying to reduce the volatile organic solvents (VOCs) which generally are the major portion (approx. 80% of the total content) of the reaction vessel as compare to the reactants/reagents, and also has the tendency to escape into the environment, which in turns contribute to ozone depletion as well as smog in urban areas, and hence extremely dangerous for mankind [5]. Therefore, great efforts are being put forward to reduce these hazardous VOCs, and the corrosive acid catalysts, participating in the reaction to make the chemical processes even more sustainable and environmentally friendlier [6]. To this context, over the past few decades, several surrogates for instance water, ionic liquids, supercritical fluids, and switchable solvents in addition to many green strategies such as ultrasound, flow chemistry, biocatalysis, microwaves, and multi-component etc., have successfully been developed [7–9]. Generally, water is thought to be an archetype solvent as it enjoy many classical properties, nonetheless it not only suffer from insolubility issues with the majority of organic compounds but also has a difficulty of removing it after the completion of the reaction because of its high boiling point, and even in many cases compounds gets decompose into the water in addition, some reactions for example amidations and transesterifications, can not be performed in water because of competing product hydrolysis [10]. On the other hand, supercritical fluids which possess low vapor pressure along with the advantages of easy disposal/removal, and recycling, are thought to be the best eco-friendly substitutes of VOCs, but, they requires more sophisticated equipment to perform the reaction. To this context, researchers turn their attention towards the ionic liquids due to their remarkable physiochemical properties but owing to their high cost as well as involvement of the non-renewable resources besides purification before their usage make them of bit doubt from green perception [11]. Consequently, bearing in mind, the urgency of the suitable alternative green solvents in place of conventional solvents to carry out the crucial synthetic transformations for sustainable development in R and D and also for the chemical industry, Abbott's 2003 discovery of the deep eutectic solvents (DESs), also known as low transition temperature mixtures (LTTMs), or low-melting mixtures (LMMs) or deep eutectic ionic liquids (DEILs), has become one of the strongest pillars to the modern synthetic community. Generally, in DES, two/three components are mixed in an appropriate amount to generate a eutectic mixture with lower melting point as compare to the individual components being used [12–15]. As a consequence, an infinite number of melts involving different compositions/components with

**8**

Stille, Sonogashira, Suzuki, and Heck coupling reactions, Biginelli reaction, 1,3-dipolar reaction, in addition to its applicability for the synthesis of quinolines, arylhomophthalimides, prymidopyrimidinediones, tetrahydropyrimidinones, hydantoins, dihydropyrimidinones, quinazolines, and a variety of functionalized indole systems with excellent selectivity in decent yields. Interestingly, the beauty of this method is its double and triple role in the reaction vessel to facilitate the accomplishment of the reactions in a clean and smooth fashion without the involvement of any catalyst/additives or solvent. In short, after a brief introduction related to the sustainability and green synthetic approaches, herewith, we have tried to display a deep survey of what has already been done in this field, and open the opportunities to the young researches to find out the new advances by employing this DES and also medium engineering might be utilized to optimize the synthetic utility of various other combinations of the DESs. Green chemistry 12 principles as well as the achievements made by employing a low melting mixture of DMU/TA in the domain of synthetic organic chemistry are displayed in the **Figure 1**.
