Chương 3 4 5: DUNG MÔI XANH

CHAPTER 3,4,5: GREEN CHEMISTRYSOLVENT 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) toxic, flammable 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 * Structure Anion [BF4]¯ [PF6]¯ Cation 35 * Solubility Thermal stability Properties of Ionic Liquids Viscosity Melting point 36 * 37 Scheme 18 General route for ILs synthesis: (path A) metathetic exchange of anion, (path B) neutralisation of base with Brønsted acids, (path C) direct alkylation of alkylimidazole, (path D) the carbonate method First step: The Synthesis of [BMIM][Br] 1-methylimidazole 20ml 1-bromobutane 30ml _ Use microwave and condenser 1-butyl-3-methylimidazolium _ Stop and cool every 5s (5 times) bromine _ Continuous stirring Cooling Undesired material and solvent Undesired material and solvent Solvent First washing Second washing Vacuum rotary evaporating 39 [BMIM]Br Ethyl acetate (3 times, 30minutes/time) Diethyl ether (3 times, 30minutes/time) t = 70oC At room temperature Second step: The Synthesis of [BMIM][PF6] [BMIM]Br 50ml HPF6 40ml H2O 50ml / cooling Reacting _ Continuous stirring in – 8h _ Keep temperature at – 10oC H2O 50ml Washing H2O H2O _ Continuous stirring _ Add 50 ml H2O until neutral, test by phenol paper _ Keep temperature at – 10oC Decanting Vacuum rotary evaporating 40 [BMIM]PF6 t = 70oC * 41 Special properties • Essentially no vapour pressure potential replacements for volatile organic solvents • Good thermal stability (most liquids thermally stable >200 ºC) not decompose over a large temperature range 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 enhance reaction rate to a great extent • High potential for enantioselective reactions (chiral ionic liquids) 36 Normalised solvent polarity scale (ET(30) = 0.00 for Me4Si and ET(30) = 1.00 for H2O)—reproduced by permission of The Royal Society of Chemistry 44 45 * Tổng hợp xúc tác * Kỹ thuật điện hố * Hố phân tích * Năng lượng * Sinh hoá * Xúc tác enzyme * Tổng hợp protein * Quá trình biomass * Kỹ thuật tách chiết * 39 Green aspects • High solubility only small reactor volumes reducing waste from synthetic are required processes • Poorly co-ordinating ions great potential for very high recovery and hence recycling of the solvent • No effective vapour pressure ionic liquids, even if used at high temperatures, not release harmful vapours 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 ... often below room temperature 33 34 * Structure Anion [BF4]¯ [PF6]¯ Cation 35 * Solubility Thermal stability Properties of Ionic Liquids Viscosity Melting point 36 * 37 Scheme 18 General route for... (chiral ionic liquids) 36 Normalised solvent polarity scale (ET (30 ) = 0.00 for Me4Si and ET (30 ) = 1.00 for H2O)—reproduced by permission of The Royal Society of Chemistry 44 45 * Tổng hợp xúc tác... Critical point • 74 LIQUID GAS Triple point • CO2 Temperature (K) 30 3 17 Pressure (bar) SOLID SUPERCRITICAL FLUID Critical point • 74 LIQUID Triple point • GAS Temperature (K) 30 3 18 Pressure (bar)