ZnCl2/phosphonium halide:: An efficient Lewis acid/base catalyst for the synthesis of cyclic carbonate

An efficient Lewis acid/base catalyst composed of ZnCl2 and phosphonium halide ([PR1R2R3R4]X-+(-); X = Cl, Br, I) was developed and showed high activity and selectivity for the coupling reaction of CO2 and epoxide under the mild conditions. The effects of reaction temperature, CO2 pressure, various compositions of the catalysts have been investigated systematically. It was found that a 96.0% conversion of propylene oxide (PO) and high turnover frequency (TOF) value (4718.4h(-1)) could be achieved in the presence of ZnCl2/PPh3C6H13Br (molar ratio = 1:6) at a low constant pressure of CO2 (1.5 MPa) and mild temperature (120 degrees C) without any organic solvents, the catalyst was also proved to be applicable to other terminal epoxides. Additionally, the catalyst could be reused with little loss of catalytic activity after five times. (c) 2006 Elsevier B.V. All rights reserved.