Halide aided synergistic ring opening mechanism of epoxides and their cycloaddition to CO2 using MCM-41-imidazolium bromide catalyst

Abstract

Imidazole was immobilized on MCM-41 using 3-chloropropyltriethoxysilane (CPTES) as the anchoring agent followed by alkylation with 1,2-dibromoethane at 110°C. The resulting catalyst was designated as MCM-41-Imi/Br. The catalyst was used for the synthesis of cyclic carbonates via cycloaddition of CO2 with several epoxides under solvent free condition. The use of MCM-41-Imi (without bromide ion) to catalyze the reaction led to the elucidation of the reaction mechanism involved in the synergistic catalysis. The catalyst was used in the cycloaddition of styrene oxide, epichlorohydrine, glycidol, allyl glycidyl ether and phenyl glycidyl ether. A high yield and excellent selectivity of cyclic carbonates were obtained under optimized conditions. The yields of the respective cyclic carbonates were 98.8% for styrene oxide, 97.0% for epichlorohydrin, 98.3% for glycidol, 97.5% for allyl glycidyl ether, 96.7% for phenyl glycidyl ether and 100% for 1,2-epoxyhexane.