Synthesis of styrene carbonate catalyzed efficiently by zinc bromide and tetra-n-butylammonium halides

In this paper chemical fixation of CO2 Was introduced for the synthesis of cyclic carbonate. Styrene carbonate can be synthesized via two routes, one is the cycloaddition of CO2 to epoxides and the other is oxidative carboxylation of styrene. The latter route couples the two processes, epoxidation of styrene and subsequent cycloaddition of CO2 to the epoxide formed. In the present work, it is shown that a catalyst system of ZnBr, and n-Bu-4 NX (X = Br, I) has an excellent activity and selectivity for the cycloaddtion of CO2 to styrene oxide. At the n-BU4NI/ZnBr2 molar ratio of 2, styrene oxide is quantitatively transformed to styrene carbonate with in a very short time(30 min). This catalyst system can be also applied for the oxidative carboxylation of styrene by combining with an epoxidation catalyst of Au/SiO2. Under the mild reaction conditions(80 degrees C, 4 h, CO2 pressure 1 MPa), styrene carbonate was obtained in a yield of 42% without any organic solvent. In separate runs, it was found that Au/SiO2 is active for the epoxidation of styrene, and ZnBr2 and n-Bu4NBr cooperatively catalyze the subsequent CO2 Cycloaddition to epoxide. The styrene carbonate yield obtained in the present study is the highest among those reported, but it is not still satisfactory for practical application.