Electroactivation Of CO₂ And Synthsis Of Organic Carbonate Under Mild Conditions

The reduction of CO₂ has been studied in this dissertation. Electrochemical character and kinetics of CO₂ in acetonitrile have been investigated by cyclic voltammetry and chronocoulometry.The mechanisms of electrochemical reduction of CO₂ have been presumed. In addition, the reduction of CO₂ in ionic liquid also has been studied by cyclic voltammetry and differential pulse voltammetry.The electrochemical experiments were performed by using a copper as working electrode, a Pt wire as auxiliary electrode and an Ag/AgI electrode as reference. CV showed that CO₂ was reduced at the potential of -2.2V, which got one electron and became an anion radical.The reduction of CO₂ at copper was an irreversible process and cyclic voltammetrygrams at different scan rates showed that it was controlled by diffusion. Difusion coefficient of CO₂ in acetonitrile obtained by employing chronocoulometry at 25℃ was 8.981×10^-6 cm²s^-1.The electrosyntheses of propylene carbonate were controlled under constant current and the processes were carried out in one-counterpart cell with inert material as cathode, active metal as anode. The effects of supporting electrolyte, electrode, current density, charge, concentration of substrate on yield have been studied. The results showed that halide ions of supporting electrolyte was essential for the reaction, which could make the ring of propylene oxide open, and the best supporting electrolyte was TEAL The highest yield was 46.2% under the optimized condition.The electrosyntheses of dimethyl carbonate(DMC) were controlled under potentiostatic and the processes were carried out in one-counterpart cell with copper as cathode, Mg as anode and Ag/AgI as reference. The effects of supporting electrolyte, electrode, current density, charge, concentration of substrate on yield have been studied. The highest yield was 14.9% under the optimized condition.Ionic liquid, BmimBF₄, was investigated as a solvent and catalyzer in the reaction. The highest yield of DMC in pure BmimBF₄ was 30.32% and it was 45.43% in the mixure of 7 mL BmimBF₄ and 3 mL MeCN.The four points listed below reflect the innovation of this dissertation. (1) Organic carbonate was produced from CO₂ and alcohol directly, which avoided the use of toxic phosgene and CO compared with the traditional organic methods as well as utilized the greenhouse gas as material. (2) Organic carbonate was synthesized by the green method of electrochemistry, which was a environmentally benign process compared with the traditional way needing sharp condition and industry method demanding high temperature and pressure.(3) The cylindrical stainless steel and copper electrode which are used as cathode are easier to be prepared and and cheaper than Pt electrode frequently used in the electrochemical reduction of CO₂ and make the process possible to industrialize.(4) Ionic liquids, as a kind of solvent and catalyzer, were applied to electrochemical research. Ionic liquids are easier to be produced and purified than traditional supporting electrolytes, and can be easily functionalized according to different demands. The application of ionic liquids gives high yield and current efficient of organic carbonate and it can be cycled as well.