MEDCHEM E CHEMBIO Lecture 9 Green Chemistry

• Green Chemistry


  Sustainable chemical synthesis
• Biocatalysis


  Use of enzymes as catalysts
• Three classes that must be in balance


  • Planet
  • People
  • Profit
• Atom economy


  Molecular weight of desired product / Molecular weight of all reactants x 100
• Atom economy is not the same as chemical yield: a high-yielding process can still result in substantial byproducts
• Reaction yield


  Quantity of product isolated / Theoretical quantity of product x 100
• In some reactions, byproducts can be formed which can be dangerous and result in waste of substances
• In an ideal reaction, all atoms are incorporated into the desired product with no waste
• 1. factor (environmental factor)


  Measures the total amount of solvents, reagents, and consumables used in kilograms and divides it by the kilograms of final product produced
• The "greenness" of a process is summarized by the E-factor
• Pfizer's process changes for the production of pregabalin


  • 90% reduction in solvent, 50% reduction in starting material, E-factor reduced from 86 to 17
• Biological reactions are usually catalysed by ENZYMES
• Enzymes are composed of amino acids which (apart from glycine) are all chiral, hence enzymes can be used as chiral tools to discriminate between two enantiomers
• Biocatalysis


  • Excellent tool for manufacturing biologically active compounds with chiral centers
  • Integrated by pharmaceutical companies with traditional medicinal chemistry
  • Selective, high yields, reusable, avoid use of heavy metals, can be used in aqueous solutions, need mild temperature and conditions
• Some substances are not soluble in water while the enzyme is, so using enzymes does not solve all problems but requires further work
• Catalysts, including biocatalysts, provide solutions for the problem of waste and create more energy efficient and less raw material consuming processes
• Six classes of enzymes


  • Oxidoreductases
  • Transferases
  • Hydrolases
  • Lyases
  • Isomerases
  • Ligases
• Glycine is the only non-chiral amino acid in enzymes
• A catalyst might not always be an enzyme
• The byproduct of the "green" process is just water
• The petrochemical carbon cycle is not sustainable, while the bio-based circular economy is more sustainable

  
• Sustainable technology requires using natural resources at rates that do not deplete supplies and generating residues at rates that can be readily assimilated by the natural environment
• Switching to renewable biomass as a feedstock will reduce the carbon footprint of chemicals and liquid fuels
• The carbon cycle needs to be brought into balance by replacing the slow formation of oil from plant biomass in geological reservoirs with direct conversion of plant biomass to biofuels and chemical products

  
• Using first-generation biomass feedstocks like corn and edible oil seeds is not sustainable as it competes with food production

  
• A possible solution is the valorization of waste biomass generated as agricultural residues using resource-efficient chemo- and biocatalytic processes

  
• First- and second-generation bioethanol