The Role of Inorganic Oxide Supports in Synthesis of Cyclic Carbonates from Carbon Dioxide and Epoxides

An inorganic oxide support coupled with a quaternary ammonium salt is an efficient catalyst for the cycloaddition of CO2 and epoxide to produce cyclic carbonates under relatively mild reaction conditions (90 degrees C, 4 MPa). When tetrabutylammonium bromide (TBAB) was used alone, the activity of the cycloaddition reaction between carbon dioxide and epoxide was only moderate. When an inorganic oxide, especially one that has abundant surface hydroxyl groups was also employed, the reaction was accelerated significantly. This demonstrated that the inorganic oxide and TBAB had a strong synergetic effect for the cycloaddition reaction. Silica was chosen as a model oxide to study the role of surface hydroxyl groups in the reaction. When the surface of silica was silylated with trimethylchlorosilane or dimethyldichlorosilane, the catalytic activity decreased sharply due to surface silylation, which indicated clearly that the surface hydroxyl groups on the silica played a decisive role in influencing the catalytic activity.