Ionic liquids containing carboxyl acid moieties grafted onto silica: Synthesis and application as heterogeneous catalysts for cycloaddition reactions of epoxide and carbon dioxide

A series of carboxyl-group-functionalized imidazolium-based ionic liquids (CILs) were synthesized and grafted onto silica gel. The catalytic activity of the resulting heterogeneous catalysts toward the synthesis of cyclic carbonateviacycloaddition reactions of epoxide and CO2 was studied. The effect on the reaction of the grafted ILs' structures and the reaction conditions such as reaction temperature, time, pressure, and the amount of catalyst used, were systematically investigated. For comparison, silica-grafted imidazolium-based ILs with and without hydroxyl groups were also used to catalyze cycloaddition reactions. The carboxylic acid group in the catalyst was demonstrated to have a synergistic effect with halide anions. A high yield of cyclic carbonates and excellent selectivity could be obtained under optimized conditions.