Synthesis Of Cyclic Carbonates From Epoxides And CO₂ Via The Synergistic Action Of Electrogenerated Magnesium And Supporting Electrolyte

Utilization and emission reduction of carbon dioxide has become a topical issue in recent years, synthesis of cyclic carbonates from epoxides and CO2 is an effective way of utilization of carbon dioxide.A novel and efficient electrocatalysis route for synthesis of cyclic carbonates CO2 and epoxides via the synergistic action of support electrolyte and electrogenerated magnesium has been developed. What the paper studied was summarized as follows:Synthesis of cyclic carbonates from epoxides and CO2 via the synergistic action of 1-butyl-3-methylimidazolium bromide and electrogenerated magnesium was studied. Effects of synthesis conditions, such as current density, electricity quantity, carboxylation temperatures and time have been explored and then the reaction mechanism was discussed. Under the optimized condition, the yield of styrene carbonate can achieve 90.75% and the applicability of the electrocatalysis route for synthesis of cyclic carbonates has been proved to be good. Synthesis of cyclic carbonates from epoxides and CO2 via the synergistic action of tetraalkylammonium halide and electrogenerated magnesium was investigated, and the effects of electrolyte’s cation and anion parcel on the yield was discussed.The results of the experiments showed that catalytic activity of electrogenerated magnesium salt under N2 is apparently stronger than that of under CO2 and MgBr2. The effects of the quaternary ammonium cations on the carboxylation of epoxide and CO2 was investigated. It can be found that the yield of cyclic carbonate decreased with the growth of the carbon chain of quaternary ammonium cation. The reason was speculated that the electrostatic attraction between quaternary ammonium cation and bromide ion decreases with the increasing of carbon chain of quaternary ammonium cation, which results in the increasing of the electrostatic attraction between magnesium ion and bromide ion and thus weakening the eletrophilicity of magnesium ion, which is unfavourable to the ring-opening of epoxide. DFT calculation confirmed that the eletrophilicity of magnesium ion formed before the ring-opening of epoxides will decrease with the growth of the carbon chain of the quaternary ammonium cation. The nucleophilicity of the oxygen anion of the intermediate formed after the ring-opening of epoxide weakens with the growth of the carbon chain of quaternary ammonium cation, which is unfavourable to the nucleophilic insert reaction of CO2.