Development in the green synthesis of cyclic carbonate from carbon dioxide using ionic liquids

This brief review presents the recent development in the synthesis of cyclic carbonate from carbon dioxide (CO₂) using ionic liquids as catalyst and/or reaction medium. The synthesis of cyclic carbonate includes three aspects: catalytic reaction of CO₂ and epoxide, electrochemical reaction of CO₂ and epoxide, and oxidative carboxylation of olefin. Some ionic liquids are suitable catalysts and/or solvents to the CO₂ fixation to produce cyclic carbonate. The activity of ionic liquid is greatly enhanced by the addition of Lewis acidic compounds of metal halides or metal complexes that have no or low activity by themselves. Using ionic liquids for the electrochemical synthesis of the cyclic carbonate can avoid harmful organic solvents, supporting electrolytes and catalysts, which are necessary for conventional electrochemical reaction systems. Although the ionic liquid is better for the oxidative carboxylation of olefin than the ordinary catalysts reported previously, this reaction system is at a preliminary stage. Using the ionic liquids, the synthesis process will become greener and simpler because of easy product separation and catalyst recycling and unnecessary use of volatile and harmful organic solvents.