ZnBr2-Ph4PI as highly efficient catalyst for cyclic carbonates synthesis from terminal epoxides and carbon dioxide

TLDR: In this article, the catalytic performance of ZnBr 2 and different phosphonium salts were examined for solvent-free synthesis of cyclic carbonates from CO 2 and terminal epoxides under mild conditions.

Abstract: The catalyst systems composed of ZnBr 2 and different phosphonium salts were examined for solvent-free synthesis of cyclic carbonates from CO 2 and terminal epoxides under mild conditions Among the catalysts investigated, ZnBr 2 –Ph 4 PI was found to be the best while those of ZnBr 2 –phosphine oxide (Bu 3 PO or Ph 3 PO) show no catalytic effect It is apparent that the halide ions of phosphonium salts have an essential role to play in the reaction The catalytic activity of ZnBr 2 –Ph 4 PI increases with a rise of Ph 4 PI to ZnBr 2 molar ratio up to 6, above which there is little change in catalytic activity We observed that with a rise in ZnBr 2 to Ph 4 PI molar ratio, there is increase in epoxide conversion but decline in TOF PO (estimated based on the site number of Zn 2+ ) The effect of water on the reaction was investigated for the first time We found that the presence of even a trace amount of water would result in a marked decline in reactivity, and the observation provides a valid explanation for why reproducibility of results is poor among researchers so far The influences of other parameters such as reaction temperature and CO 2 pressure on the catalytic performance of ZnBr 2 –PPh 4 I were also studied It is shown that the catalyst is sensitive to reaction temperature, and a rise of reaction temperature up to 130 °C favors the formation of cyclic carbonates We observed that activity increases with rise in CO 2 pressure and reaches a maximum at an initial CO 2 pressure of 25 MPa Moreover, a plausible reaction mechanism has been proposed