Succinimide-KI: An efficient binary catalyst system for mild, solvent-free cycloaddition of CO2 to epoxides

In this study, we have for the first time demonstrated that succinimide (SI)-KI is an efficient catalyst system to synthesize propylene carbonate (PC) from carbon dioxide (CO 2 ) and propylene oxide (PO) at a solvent-free condition. A synergistic effect was observed between SI and KI that largely increased the reaction yield. It enabled the cycloaddition reaction to take place at 70 °C under a low pressure (0.4 MPa) for only 4 h, with a PC yield as high as 97.5%. The overall condition is milder than the reaction catalyzed by most of the other KI involved co-catalyst systems reported in literatures. The excellent catalytic ability was explained by the increased KI solubility in PO due to the presence of SI and the weak acidity of NH in SI which can be enhanced by KI. A reaction mechanism was proposed based on a reaction kinetics study. SI-KI was applicable to cycloaddition of CO 2 with other epoxides. It may offer an inexpensive, environmentally-friendly route to synthesis of propylene carbonate from CO 2 .