CHAPTER V. Part A GREEN CHEMISTRY ORGANIC SYNTHESIS IN AQUEOUS MEDIUM: An introduction

Transcription

1 CHAPTE V GEE CHEMISTY GAIC SYTHESIS I AQUEUS MEDIUM: An introduction

2 V.A.1 Brief introduction to green chemistry The need of development of the concept of green chemistry to help safeguard human life started after the first chemical revolution, which changed modern life with excellent amenities and services, but also created the serious problem of environmental pollution. Thus, The core principle of this concept is to protect the environment, not by cleaning it up, but by discovery of new chemistry and pharmaceutical industries to concern the effect on human life when new chemicals are introduced into our society. 1,2 In early 1990 s, Green chemistry is defined as the utilization of a set of principles that reduces or eliminates the use of hazardous substances in the design, manufacture and application of chemical products. 3 The term Green Chemistry was coined in 1991 by Prof. Paul T. Anastas. 4 Green chemistry is the largest and multifaceted field in chemistry. Thus the use of the principles of green chemistry can be evaluated the greenness of a particular synthetic protocol. 1 These principles have given a solution for several issues, such as preventing the use of volatile and toxic solvents i.e. less hazardous chemical reactions, the quantity and reusability of catalyst and reagents employed i.e. stoichiometric reagents, the use of benign chemicals, atom efficiency or atom-economy synthetic methods with a minimum number of chemical reaction steps in which the selected step generates the desire product without producing any by products, energy efficient and mild reaction conditions, and prevent the chemical waste produced (Figure V.A.1). 5 Figure V.A.1 Principles of green chemistry. 178

3 Green Chemistry is a branch of chemistry which involves pulling together tools, techniques and technologies. It is helpful to chemists and chemical engineers in research, development and production for development of more eco-friendly and efficient methods which may also have significant financial benefits. It is now going to become an essential tool in the field of synthetic chemistry, and the development of Green Chemistry redefines the role of a solvent: An ideal solvent facilitates the mass transfer but does not dissolve. In addition, a desirable green solvent should be natural, nontoxic, inexpensive and readily available with additional benefits of aiding the reaction, separation or catalyst recycling. 6,7 The most challenge in chemistry to develop practical processes, reaction media, conditions and/or utility of materials based on the idea of green chemistry is one of the important issues in the scientific community. 8 V.A.2 rganic synthesis in water Although water is considered to be a problem for organic synthesis and the purification processes and drying in final products is very cumbersome, in recent years water is considered to be a good solvent for organic reactions. The most interesting example of water as a solvent in the synthetic routes of the Diels-Alder reactions in which the hydrophobic properties of some reagents makes water an ideal solvent. 9 Water as a solvent accelerates some reactions and it has been proved to be very good for selectivity even for reagents which are not very soluble or insoluble in it and this is a so-called hydrophobic interaction, which is well known in biology, notably for the 10, 11a interaction of peptides. Water appears to be a better option compared to others green solvents because of its abundant, non-toxic, non-corrosive, and non-inflammable nature. In addition, water can be contained because of its relatively high vapor pressure as compared to organic solvents, making it a green 11, 12 and sustainable alternative. ecently, organic reactions in water without use of harmful organic solvents have drawn much 13, 14 more attention, because water is cheap, safe and environmentally benign solvent. 179

4 V.A.3 Literature survey on organic reactions in aqueous media Some important organic reactions in aqueous media are presented below: V.A.3.1 Synthesis of pyrazolo[3,4-b]pyridines via multicomponent reaction Li-Qiang, W et al. have reported a simple and an efficient synthesis of 4-aryl-3-methyl-1-phenyl- 1H-benzo[h]pyrazolo[3,4-b]quinoline-5,10-diones by the one-pot condensation of 3-methyl-1- phenyl-1h-pyrazol-5-amine, aldehydes and 2-hydroxynaphthalene-1,4-dione in water in the presence of diammonium hydrogen phosphate (Scheme V.A.1). 15 H 2 H + CH + (H 4 ) 2 HP 4 H 2, eflux Scheme V.A.1 V.A.3.2 ne-pot green synthesis for pyrimido[4,5-d]pyrimidine derivatives A practically convenient and eco-friendly synthesis of pyrimido[4,5-d]pyrimidines has been developed by Mazaahir, K et al. in an aqueous medium without using any catalyst, i.e. completely circumventing the use of hazardous organic solvents and corrosive acids or bases from barbituric acid, aldehyde and urea or thiourea (Scheme V.A.2). Water-insoluble solid products obtained in short time are found to be essentially pure and are obtained in very high yield. 16 H H + CH + = or S H 2 H 2 water MW H H H H Scheme V.A.2 180

5 V.A.3.3 Green synthesis of hexa-hydro triazines under sonic condition An efficient, clean and quick methodology for the synthesis of various 1,3,5-hexahydrotriazine derivatives with greater yields than the previously reported conventional methods has been developed by Ashish K Singh et al. from aryl amines, and formaldehyde under ultrasonic condition (Scheme V.A.3) H HCH EtH/ H 2 )))) = Cl, Me, 2, H 2, H, CH 3 Scheme V.A.3 V.A.3.4 ovel synthesis of anilines by zinc metal-mediated chemoselective reduction of nitroarenes in water Takehito T et al. have reported a simple and low cost procedure for reducing nitroarenes to the corresponding anilines using zinc metal and H 4 Cl in water without any organic solvent at 80 C (Scheme V.A.4) and this procedure is chemoselective for nitro groups. Ester, amide and halide substituents on aromatic rings are unaffected. 18 Zn/ H 4 Cl 2 H H 2 2, 80 o C Scheme V.A.4 181

6 V.A.3.5 Synthesis of 4,6-substituted coumarins by Heck reaction in water Talita, de A et al. have reported the synthesis of 4,6-substituted coumarins by one pot palladium-catalyzed Heck-lactonization reaction involving ortho-iodophenols and methyl crotonate or a Z-enoate derived from d-mannitol in water using triethylamine as base (Scheme V.A.5). 19 H I = H, Ph, PdCl 2 / Et 3 CEt H 2, 80 o C 1 2 Scheme V.a.5 V.A.3.6 Suzuki reaction in aqueous media A simple and efficient protocol has been developed by Chun, L et al. for the PdCl 2 catalyzed Suzuki reaction of aryl bromides or nitrogen-based heteroaryl bromides with arylboronic acids in good to excellent yields in aqueous ethanol (Scheme V.A.6). It is noteworthy that the presence of water could reverse the role of atmosphere on the palladium-catalyzed ligand-free Suzuki reaction. 20 Ar Br + B(H) 2 EtH /H 2 (1:1 ), rt 0.5 mol% PdCl 2 Ar Scheme V.A.6 182

7 V.A.4 Conclusions As we can see from the above Literature survey, Green Chemistry principles have advanced considerably in the last decades. esearch on various industrial applications has been very successful and with considerable advantages for energy consumption, toxic products and minimum waste. These advantageous have contributed in the safety and health of workers who work in chemical industries, making of products with basic materials workshops. Secondly, green chemistry has found alternative ways to cut energy consumption by changing processes, or through new catalytic routes, in order to save energy. Thirdly, the use of alternative solvents in green chemistry has reduced substantially environmental problems and it is better to use green solvent with its benefits like less toxicity, less hazards, more safer rather than other organic solvents (THF, DME, MTBE) for industrial applications. Fourthly, green chemistry has introduced innovations for the industrial products during their use or after their useful life cycle as waste. 183

8 V.A.5 eferences 1. Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice, xford University Press, xford, Poliakoff, M.; Licence, P. ature, 2007, 450, US EPA website, EPA s Green Chemistry Program, ry/index.htm 4. Anastas, P. T.; Warner, J. C. Green Chemistry Theory and Practice, xford Univ. Press, ew York (1998). 5. Polshettiwar, V.; Varma,. S. SC Green Chemistry o.7: Aqueous Microwave Assisted Chemistry: Synthesis and Catalysis, oyal Society of Chemistry Ahluwalia, V. K.; Kidwai, M., ew Trends In Green Chemistry, Anamaya publisher ew Delhi, 2 nd edition, 2007, 5-18, Ahluwalia, V. K., Green Chemistry Environmentally Benign eactions, published by India books, 2 nd edition, 2006, Tundo, P.; Anastas, P. T. Green Chemistry: Challenging Perspectives, xford Science: xford, Laue, T.; Plagens, A. amed rganic eactions, 2nd ed.; Wiley: Chichester, UK, 2005; pp Voet, D.; Voet, J. G.; Pratt, C. W. Fundamentals of Biochemistry: Life at the Molecular Level; Wiley: Hoboken, J, USA, 2006; pp (a) Clark, J. H. Green Chem. 2006, 8, 17; (b) Li, C. J.; Chen, L. Chem. Soc. ev. 2006, 35, 68; (c) Polshettiwar, V.; Varma,. S. J. rg. Chem. 2008, 73, 7417; (d) Polshettiwar, V.; Varma,. S. J. rg. Chem. 2007, 72, (a) Polshettiwar, V.; Varma,. S. Chem. Soc. ev. 2008, 37, 1546; (b) Dallinger, D.; Kappe, C.. Chem. ev. 2007, 107, 2563; (c) Pol-shettiwar, V. ; Varma,. S. Alternative Heating for Green Synthesis in Water (Photo, Ultrasound, and Microwave), Hand book of Green Chemistry, ed. Anastas, P. T.; Li, C.-J. Wiley-VCH Verlag GmbH, Weinheim, 2009; (d) Varma,. S. Clean chemical synthesis inwater, rg. Chem. Highlights 2007, 184

9 13. Bigi, F.; Chesini, L.; Maggi,.; Sartori, G. J. rg. Chem. 1999, 64, Bigi, F.; Conforti, M. L.; Maggi,.; Piccinno, A.; Sartori, G. Green Chem. 2000, 2, Li-Qiang, W.; uo-yi, D.; Chun-Guang, Y.; Fu-Lin, Y. J. Chinese Chem. Soc. 2010, 57, Mazaahir, K.; Kavita, S.; Shuchi, K. Z. aturforsch. 2007, 62b, Ashish, K. S.; Sudhish, K. S.; Mumtaz, A. Q. J. Mater. Environ. Sci. 2011, 2, Takehito, T.; Hirohisa, T. Green Chem. 2001, 3, Talita, de A. F.; ita, de C. C. C.; Tatiana, M. D. G.; Alcides, J. M. da S.; Paulo,.. C. Tetrahedron Lett. 2008, 49, Chun, L.; Qijian,.; Pingping, H.; Jieshan, Q. rg. Biomol. Chem. 2011, 9,