Electrochemical Synthesis Of Organic Carbonate From Carbon Dioxide In Ionic Liquid

Carbon dioxide (CO2) produced by combustion of fossil fuels is regarded as the most significant greenhouse gas; the increasing accumulation of CO2 in the atmosphere has caused serious environmental problems. On the other hand, CO2 is a naturally abundant, economical, non-toxic and recyclable carbon source. Thus, the conversion and utilization of CO2 have attracted considerable attention in the whole world. The electrocarboxylation of various organic compounds with CO2, which can replace phosgene and cyanides, is an environmental friendly and attractive approach to prepare valuable carboxylated products.Ionic liquids, molten salts with melting points close to room temperature, are obtained by combination of large organic cations with a variety of anions. Recently, ionic liquids have been used as green reaction media in organic synthesis due to their wide electrochemical potential window, high ionic conductivity, good solvating ability and low vapour pressure.Electrochemical activation of CO2 to useful chemical products under mild condition is a simple procedure. Specially, fixation of CO2 by electrocarboxylation in ionic liquid is of great practical significance. What the paper studied may be summarized as follows:1. In this paper, the research progress of both current status of CO2 emission and strategies for CO2 conversion and utilization were reviewed, the electrocarboxylation of CO2 with organic compounds was introduced in detail, applications of ionic liquid in fixation of CO2 was also explained.2. The electrochemical reduction behavior of CO2 on Cu electrode in ionic liquid, 1-butyl-3-methylimidazoliumtetrafluoborate (BMIMBF4), during the synthesis of dimethyl carbonate (DMC) was studied. The experiments were carried out in three electrodes undivided cell under mild conditions, and the use of volatile solvents and catalysts was avoided. The electrochemical reduction behavior of CO2 on Cu electrode in BMIMBF4 had been studied by cyclic voltammetry and the reduction process was mostly controlled by diffusion. DMC was obtained in 73.2% faradaic efficiency, under the optimized condition.3. A new procedure for the electrocatalytic carboxylation of 2-amino-5-bromopyridine with CO2 in ionic liquid BMIMBF4 to 6-aminonicotinic acid was investigated. The experiments were carried out in three electrodes undivided cell under mild conditions, and the use of toxic solvents and catalysts, as well as any other additional supporting electrolytes, was avoided. The electrochemical reduction behavior of 2-amino-5-bromopyridine in BMIMBF4 had been studied by cyclic voltammetry and the reduction process was controlled by diffusion. 6-aminonicotinic acid was obtained in 75% yield, under the optimized condition. The results showed that the yields were strongly affected by various factors:temperature, potential, charge passed, electrode material and substrate concentration. Moreover, the ionic liquid was successfully recycled.4. A novel procedure for the electrocatalytic carboxylation of aromatic ketones with carbon dioxide in ionic liquid BMIMBF4 toα-hydroxy carboxylic acid methyl ester was developed for the first time. The electrochemical behavior of acetophenone in BMIMBF4 was studied by cyclic voltammetry and the reduction process was controlled by diffusion. The electrolyses experiments were carried out in an undivided cell under mild conditions without any toxic solvents, catalysts and supporting electrolytes, followed by addition of an alkylating agent, affording the a-hydroxycarboxylic acid methyl ester in a moderate yield (62%). The results showed that the yields were strongly affected by various factors:temperature, current density, charge passed, electrode material and substrate concentration. Moreover, the ionic liquid was successfully recycled for this reaction.5. A simple and efficent procedure for electrocatalytic dimerisation of benzoyl chloride in ionic liquid BMIMBF4 to benzil was investigated. The experiments were carried out in three electrodes undivided cell under mild conditions, and the use of volatile and toxic solvents and catalysts was avoided. The electrochemical reduction behavior of benzoyl chlorides in BMIMBF4 had been studied by cyclic voltammetry. The experiments were carried out at different electrode with different temperature and working potential. Benzil was obtained in moderate yield (51%), under the optimized condition. Moreover, the ionic liquid was successfully recycled.A new procedure for the electrocatalytic carboxylation of benzoyl bromide with carbon dioxide in ionic liquid BMIMBF4 to phenylglyoxylic acid methyl ester was investigated. The electrochemical behavior of benzoyl bromide in BMIMBF4 was studied by cyclic voltammetry with a reduction peak at-0.8 V (vs. Ag). The electrolyses experiments were carried out in an undivided cell under mild conditions without any toxic solvents, catalysts and supporting electrolytes, followed by addition of an alkylating agent, affording the phenylglyoxylic acid methyl ester.