Cycloaddition of CO2 to Epoxides Catalyzed by Carboxyl-Functionalized Imidazolium-Based Ionic Liquid Grafted onto Cross-Linked Polymer

Carboxyl-functionalized imidazolium-based ionic liquid was grafted onto cross-linked divinylbenzene polymer (PDVB-CEIMBr) for the first time. The catalyst was characterized and used for the cycloaddition of CO2 to epoxides under relatively mild reaction conditions without any use of cocatalyst and organic solvent. The effects of reaction conditions (temperature, initial CO2 pressure, and time) and water addition on the yield of cyclic carbonate were investigated systematically. Under optimal conditions (140 degrees C, initial CO2 pressure 2.0 MPa and 4 h), propylene carbonate selectivity and yield was 99.8% and 96.1%, respectively. Moreover, the catalyst shows good stability and reusability. A plausible reaction mechanism was proposed for the catalytic reaction. It is suggested that synergetic effect among Bronsted acid COOH, Lewis base Br- and the support facilitates the coupling reaction. From the viewpoint of industrial application, the catalyst is attractive because of its excellent catalytic efficiency.