Why is catalysis important in making industrialprocesses more efficient and economically profitable?• Catalytic reagents reduce the energy of thetransition state, thereby reducingWhy is catalysis important in making industrialprocesses more efficient and economically profitable?• Catalytic reagents reduce the energy of thetransition state, thereby reducingWhy is catalysis important in making industrialprocesses more efficient and economically profitable?• Catalytic reagents reduce the energy of thetransition state, thereby reducing
GREEN CHEMISTRY Dr Nam T S Phan Faculty of Chemical Engineering HCMC University of Technology Office: room 211, B2 Building Phone: 38647256 ext 5681 Email: ptsnam@hcmut.edu.vn Chapter 2: CATALYSIS AND GREEN CHEMISTRY Why is catalysis important in making industrial processes more efficient and economically profitable? • Catalytic reagents reduce the energy of the transition state, thereby reducing the energy input required for a process • Catalysts are required in small quantities • The regeneration and reversibility of catalysts are good for green processes No catalyst With catalyst With catalyst: Less energy, less toxic reagents, less waste E factor • E factor: The actual amount of waste produced in the process (everything but the desired product except water) / kg of product • A higher E factor ặ more waste ặ greater negative environmental effect Generally, the E factor increases dramatically on going from bulk to fine chemicals, and then pharmaceuticals Å multi-step syntheses + stoichiometric reagents rather than catalysts for the latter For example: Where is the waste from? • Waste generated in the manufacture of organic compounds consists primarily of inorganic salts • Consequence of the use of stoichiometric inorganic reagents • For examples: Stoichiometric reductions with metals (Na, Mg, Zn, Fe) and metal hydride reagents (LiAlH4, NaBH4) • Oxidation with KMnO4, CrO3 / H2SO4 • Sulfonations, nitrations, halogenations, diazotizations and Friedel-Crafts acylations, employing stoichiometric amounts of mineral acids (H2SO4, HF, H3PO4) and Lewis acids (AlCl3, ZnCl2, BF3) Solution to reduce waste? • Substitution of classical stoichiometric methodologies with cleaner catalytic alternatives Catalyst Stoichiometric reagents Atom efficiency / economy No catalyst 10 19 Using homogeneous catalyst Catalyst separation by column chromatography / distillation / extraction 20 Using homogeneous catalyst • More waste • More energy consumed • Less possibility to recycle and reuse • Product contaminated with toxic metals • More toxic solvents involved 21 Homogeneous Friedel-Crafts acylation 22 Heterogeneous Friedel-Crafts acylation 23 Homogeneous synthesis of 2,6dichlorobenzonitrile 24 Heterogeneous synthesis of 2,6dichlorobenzonitrile – less waste 25 26 Catalyst 27 Soluble polymer-supported catalyst •Temperature-dependent phase separation • Solvent-dependent phase separation • PEG: soluble in DMF, DCM but insoluble in ether, iPrOH 28 Superparamagnetic nanoparticle-supported catalyst A+ B C C 29 Biocatalysts Enzymes / whole-cell biocatalysts ặ catalyse organic reactions at pH 4-9, 10-50 oC, without extremes of pressure, addition of metals ặ environmentally acceptable Conventional methods ặ require highly acidic 30 or basic media, high energy input, toxic metals Advantages of biocatalysis One area where organic chemists are still struggling: chirality !!! Biocatalysts: predominantly suited for optically pure stereo-isomers Essential for drugs & agrochemicals 31 Chemo-selectivity: • Other chemically sensitive functional groups Ỉ still survive with enzyme • Biocatalytic conditions Ỉ cleaner / greener • Side-reactions avoided Æ advantageous for product purifications • Enzyme Æ react on a single type of functional group only 32 33 .. .Chapter 2: CATALYSIS AND GREEN CHEMISTRY Why is catalysis important in making industrial processes