离子液体-乙腈混合溶剂中电催化CO_2与甲醇合成碳酸二甲酯

Electrosynthesis of Dimethyl Carbonate in [bmim]BF_4-MeCN Solvent

常温常压下分别在离子液体1-丁基-3-甲基咪唑四氟硼酸盐([bmim]BF4)-MeCN混合溶剂和纯MeCN溶剂中研究了CO2在Cu电极上的循环伏安行为.结果表明,CO2均发生不可逆还原反应生成CO2-.与纯MeCN溶剂相比,在混合溶剂中CO2还原峰电位均有正移.这表明溶剂中的咪唑型离子液体对活化CO2有催化作用.在混合溶剂中,以CO2和MeOH为原料合成碳酸二甲酯(DMC),考察了[bmim]BF4/MeCN体积比、工作电极材料、MeOH浓度和电解电位等对DMC产物收率的影响.与其他DMC合成方法相比,本法反应条件温和、设备简单、合成产物收率较高.在优化的条件下,DMC产物收率可达79.6%.并提出了合成DMC可能的反应机理.

Cyclic voltammetries obtained at a Cu cathode in a CO2-saturated [ bmim] BF4-MeCN solvent and a CO2-saturated MeCN solvent were studied under mild conditions. The results showed that CO2 was reduced irreversibly to free radical anion CO2^- . The ionic liquid of the mixed solvent had catalytic activity for CO2 electrolysis. The cathodic peak of CO2 reduction shifted positively in the mixed solvent. Dimethyl carbonate （DMC） was synthesized from CO2 and MeOH in the mixed solvent in an undivided cell with a Mg anode and Cu cathode using MeI as an alkylating agent. The synthesis reaction was carried out under mild conditions. The synthesis product was very easy to be separated from the mixed solvent. The influence of the volume ratios of [ bmim]BF4 to MeCN, the electrode materials, the working potential, and the MeOH concentration on the DMC yield was examined. Under the optimal conditions, the highest DMC yield reached 79.6 %. A possible reaction mechanism for electrosynthesis of DMC was proposed.