GREEN CHEMISTRYDr Nam T. S. PhanFaculty of Chemical EngineeringHCMC University of TechnologyOffice: room 211, B2 BuildingPhone: 38647256 ext. 5681Email: ptsnamhcmut.edu.vnGREEN CHEMISTRYDr Nam T. S. PhanFaculty of Chemical EngineeringHCMC University of TechnologyOffice: room 211, B2 BuildingPhone: 38647256 ext. 5681Email: ptsnamhcmut.edu.vnGREEN CHEMISTRYDr Nam T. S. PhanFaculty of Chemical EngineeringHCMC University of TechnologyOffice: room 211, B2 BuildingPhone: 38647256 ext. 5681Email: ptsnamhcmut.edu.vnv
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 3: SOLVENT AND GREEN CHEMISTRY Solvents used in synthesis & product separation / purification Why are reactions performed using solvents? • To dissolve reactants • To slow or increase the rate of reactions • To act as a heat sink or heat transfer agent • To prevent hot spots and runaway reactions Several solvents are volatile organic compounds (VOCs) Ỉ toxic, flammable Ỉ environmental, health, and safety concerns Principle of green chemistry: Use safer solvents and reaction conditions: Avoid using solvents, separation agents, or other auxiliary chemicals If these chemicals are necessary, use innocuous chemicals 10 Synthesis with ScCO2 Organic and water layers are easily separated to leave clean product, which can be directly analyzed by 1H NMR 25 Supercritical Friedel Crafts Alkylations offer a number of advantages: • High product selectivity • Easy product separation – Heterogeneous catalyst – Supercritical fluid removed by pressure release • Clean Technology – Recycling of the supercritical fluid is possible – No toxic solvents used – Less by-products • Longer catalyst lifetime – Supercritical Fluids help prevent catalyst coking • Safety – Significant smaller reactor volumes compared to batch processes give equivalent productivity 26 Limitations of ScCO2 • Poor solubility of several polar substrates in ScCO2 • Modifiers (organic solvents) could be added to regulate solubility Æ less green • CO2-philic surfactants being developed, but expensive and have to be separated from products Ỉ less green 27 Water as green solvent 28 Advantages of water as solvent • Most inexpensive solvent • Most environmentally benign solvent • Non-flammable at all • Sometimes offers completely new reactivity • Low solubility of O2 Ỉ facilitate air-sensitive catalysis • Essential for synthesis of biological compounds from carbohydrates & chemical modification of biomolecules 29 30 31 Disadvantages • Poor solubility for nonpolar solutes • Reactive • Must be returned to the watercourseặ pollution possible Separation often energy intensive or long drying time 32 Ionic liquid as green solvent Organic salts with melting points below 100°C, often below room temperature 33 34 Special properties Essentially no vapour pressure ặ potential replacements for volatile organic solvents • Good thermal stability (most liquids thermally ( stable >200 ºC) Ỉdo not decompose over a large temperature range Ỉ convenient for reactions requiring high temperature • Able to dissolve a wide range of organic, inorganic, organometallic compounds 35 • Generally not co-ordinate to metal complexes, enzymes, organic substrates • Most of ionic liquids can be stored without decomposition for a long time • Ionic characters Ỉ enhance reaction rate to a great extent • High potential for enantioselective reactions (chiral ionic liquids) 36 Green aspects High solubility ặ only small reactor volumes are required ặ reducing waste from synthetic processes Poorly co-ordinating ions Ỉ great potential for very high recovery and hence recycling of the solvent • No effective vapour pressure Ỉ ionic liquids, even if used at high temperatures, not release harmful vapours Ỉ reducing the amount of VOCs released into the atmosphere 37 Disadvantages • Very expensive compared to conventional organic solvents (100-1000x) • Have to be made, often using solvents • Products have to be extracted using organic solvents • May have to wash with water prior to reuse 38 39 .. .Chapter 3: SOLVENT AND GREEN CHEMISTRY Solvents used in synthesis & product separation / purification