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

Abstract

An inorganic oxide support coupled with a quaternary ammonium salt is an efficient catalyst for the cycloaddition of CO 2 and epoxide to produce cyclic carbonates under relatively mild reaction conditions (90 °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. 以一系列无机氧化物与四丁基溴化铵为双组分催化剂体系, 考察了其催化 CO 2 和环氧化合物合成环状碳酸酯的反应性能. 结果表明, 在四丁基溴化铵与这些本身并没有催化活性的无机氧化物共同作用下, 反应活性明显提高, 表现出很强的协同催化作用. 另外, 通过对 SiO 2 的表面硅烷基化, 考察了其表面羟基数量对反应活性的影响, 发现当 SiO 2 的表面经过硅烷基化以后, 反应活性大幅度降低, 表明无机氧化物表面羟基对 CO 2 环加成反应活性有非常显著的促进作用. The silica and TBAB showed a strong synergetic effect for the cycloaddition reaction and hydroxyl groups on the surface of silica played a vital role in enhancing catalytic activity.