Abstract: 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 ZnBr₂ and n-Bu₄NX(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 ℃, 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.

Key words: Styrene carbonate, Styrene, Styrene epoxide, CO₂, ZnBr₂/tetra-n-butylammonium halide, Au/SiO₂