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GREEN CHEMISTRY By 1 Dr. Kandikere Ramaiah Prabhu Principal Research Scientist Department of Organic Chemistry Indian Institute of Science Bangalore – 560 012 October 23, 2010, Bangalore History….. Green Chemistry is born around 199o What is green chemistry or Sustainable Technology Traditionally - Chemical Yield was paramount Green Chemistry Focuses on Process efficiency in terms of eliminating wastes at source and avoid using or generating toxic substances 2 12 Principals of green chemistry Prevention Atom Economy Less Hazardous Chemical Syntheses Designing Safer Chemicals Safer Solvents and Auxiliaries Design for Energy Efficiency It is better to prevent waste than to treat or clean up waste after it has been created. Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product. Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment. Chemical products should be designed to effect their desired function while minimizing their toxicity. The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used. Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure. Use of Renewable Feedstocks A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable. Reduce Derivatives Unnecessary derivatization (use of blocking groups, protection/ deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste. Catalysis Catalytic reagents (as selective as possible) are superior to stoichiometric reagents. Design for Degradation Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment. Real-time analysis for Pollution Prevention Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances. Inherently Safer Chemistry for Accident Prevention Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires. 4 E-Factor??? Mass ratio of waste to desired product Higher e-factor – more waste and –ve environmental impact Raw Materials-Product output product The key to waste minimization is precision in organic synthesis, where every atom counts!!! 5 Atom efficiency Molecular weight of the product Sum molecular weight of the all products formed Atom efficiency of stoichiometric versus catalytic oxidation of alcohols 6 7 Additional questions!!?? Environmental impact of waste!! Waste can be an useful output What is the waste generated in manufacture of Organic compounds??? Fine chemicals and pharmaceuticals use stoichiometric amounts of reagents Reductions – Metal hydride Oxidations - CrO3, KMnO4,etc Sulfonation, Nitration, Friedel-Crafts reaction etc……!!!! 8 The technologies used for the production of many substituted aromatic compounds have not changed in more than a century and are, therefore, ripe for substitution by catalytic, low-salt alternatives 9 10 Two routes to hydroquinones 11 Catalysts Homogeneous catalyst & Heterogeneous catalysts Organocatalyst Biocatalysts 12 Homogeneous catalyst & Heterogeneous catalysts Organocatalyst 13 DEVELOPMENT CATALYSIS IN ORGANIC SYNTHESIS 14 If the solution to the waste problem in the fine chemicals industry is so obvious Replacement of classical stoichiometric reagents with cleaner, catalytic alternatives Why was it not applied in the past? There are several reasons for this. 15 First, because of the smaller quantities compared with bulk chemicals, the need for waste reduction in fine chemicals was not widely appreciated. A second, underlying, reason is the more or less separate evolution of organic chemistry and catalysis. Fine chemicals and pharmaceuticals have remained primarily the domain of synthetic organic chemists who, generally speaking, have clung to the use of classical “stoichiometric” methodologies and have been reluctant to apply catalytic alternatives. A third reason, which partly explains the reluctance, is the pressure of time. Fine chemicals generally have a much shorter lifecycle than bulk chemicals and, especially in pharmaceuticals, ‘time to market’ is crucial. 16 Major points to be addressed Catalysts Solvents Renewable Raw Materials – White biotechnology Risky Reagents Process integration and catalytic cascades 17 Catalysts Acid base catalyst Heterogeneous catalysts Homogeneous catalyst Solid catalysts Bio catalyst Organo catalysts 18 Acid base catalyst Montmorillonite clays 19 Zeolites 20 Reductions Catalytic reductions Hydrogen gas Hydrogenation catalysts Selectivity in hydrogenation Chiral reductions 21 oxidations 22 Biocatalysts Egs: Yeast-ADH as alcohol dehydrogenase Horse liver-ADH 23 Organocatalysis Proline-catalyzed aldol reaction 24 O Our Research…!!!! O S Mo S H3C N S S H3C Transition Metal oxides Chemical transformations Metal-oxo complexes X XO M Oxidized X MReduced Reduction XO CH3 CH3 Academia & Industry. Oxidations & reductions processes. Oxidation N Oxygen is transformed from Molecular Oxygen M. Maddani, K. R. Prabhu, Tetrahedron Lett., 2008, 49, 4526 Oxidation of Alcohols to Carbonyls Catalysed by Molybdenum Xanthate OH MoO2(Et2NCS2)2 CHO No reaction Toluene/Water Reflux, 40h Heterogeneous catalysts Liquid phases Recovery, recycling and Stability. NH2 Amm.persulphate Aq Ammonia + 1.5MHCl + in 1.5MHCl + MoO2(X)2 Acetonitrile RT, 50h Polyaniline MoO2(X)2 3 = Polyaniline Proposed polyaniline-supported MoO2(X)2 structure. Efficiency of the catalyst H OH MeO Run Catalyst 3, O2 O Toluene, Reflux, 20h Product (Yield %) MeO Recovery of PASMOX 1. 98 >99 % 2. 95 >98 % 3. 92 >96 % M. Maddani, K. R. Prabhu, Unpublished Results II Disposal or decomposition protocols for hydrazine and its derivatives by using user friendly protocols Convert surplus high energy materials to safer products 29 30 R.A. BACK, Reviews of Chemical Intermediates, 5 (1984) 293—323 C.Willis, R.A.Back, International Journal of chemical kinetics, 1977, 9, 787 IN SEARCH OF CATALYST FOR HYDROGENATION USING HYDRAZINE HYDRATE 31 METHOD FOR THE AEROBIC HYDROGENATION OF OLEFINS Method for the generation of diimide using metal Catalyst H2NNH2, CuSO4, air H2NNH2, CuSO4, H2O2 H2NNH2, CuSO4, O2 Metals such as mercuric oxide and Hexacyanoferrate(III) are also used along with hydrazine hydrate E.J. Corey, W.L. Mock .D.J. Pasto Tetrahedron Lett. 1961, 347-352 S. Huitig, H. R. Miiller, W. Thier, Tetrahedron Lett. 1961, 353. 32 33 34 From Azodicarboxylates (acid catalyzed hydrolysis) Thermal decomposition of arenesulfonyl hydrazides E. E. van Tamelen, R. S. Dewey, J. Am. Chem. Soc. 1961 83 3729 . E.J. Corey, W.L. Mock .D.J. Pasto Tetrahedron Letters 1961, 347-352 35 Flavin-Catalyzed Generation of Diimide Y. Imada, H. Iida, T. Naota, J. Am. Chem. Soc. 2005, 127, 14544-14545 Reduction of Carbon-Carbon Double Bonds Using Diimide genearted by using 36 C. Smit, M. W. Fraaije, A. J. Minnaard, J. Org. Chem. 2008, 73, 9482–9485 Flavin-Catalyzed Generation of Diimide Y. Imada, H. Iida, T. Naota, J. Am. Chem. Soc. 2005, 127, 14544-14545 Reduction of Carbon-Carbon Double Bonds Using diamide generated by an Organocatalyst 37 C. Smit, M. W. Fraaije, A. J. Minnaard, J. Org. Chem. 2008, 73, 9482–9485 38 39 40 41 MECHANISM FOR OXIDATIVE CLEAVAGE OF HYDRATE USING HYDRAZINE FLAVIN CATALYST 42 Y. Imada, H. Iida, T. Naota, J. Am Chem. Soc. 2005, 127, 14544-14545 ENVIRONMENTALLY BENIGN METHOD FOR THE AEROBIC HYDROGENATION OF OLEFINS 43 REDUCTION OF ALKENES AND ALKYNES 44 45 46 47 48 DRUGS WITH CHIRAL METHYL GROUP 49 SYNTHETIC SCHEME 50 ENANTIOSELECTIVE REDUCTION 51 Tehshik P. Yoon, Eric N. Jacobsen*, Science 2003:Vol. 299. no. 5613, pp. 1691 - 1693 Andreas Pfaltz * and William J. Drury III, PNAS April 20, 2004 vol. 101 no. 16 5723-5726 52 Conclusion P Prevent waste R Renewable raw material O Omit derivatization steps D Degradable Chemical Product U Use of safe synthetic methods C Catalytic reagents T Temperature, Pressure ambient I In – process monitoring V Very few auxiliary substrates E E-factor, atom efficiency L Low toxicity of chemical products Y Yes, it is safe 53 Acknowledgements Dr. Mahagundappa Maddani Mr. Manjunath Lamani Mr. GS Ravikumar IISc, AMRB, RL Fine Chem 54 55