Chemical Fixation of CO2 with Highly Efficient ZnCl/[BMIm]Br Catalyst System
摘要
The search for environmentally benign economic process has been the impetus for much of the research involving epoxide carbon dioxide coupling in view of the so called green chemistry and atom economy , since CO2 is a renewable resource can be used as a safe cheap C 1 building block to synthesize useful organic compounds without producing any coproducts.[1-2] One of the most attractive synthetic goals starting from carbon dioxide is the chemical fixation of CO2 onto epoxide to afford the five-membered cyclic carbonates (Scheme 1),which are excellent aprotic polar solvents are used extensively as intermediates in the production of pharmaceuticals fine chemicals.[3] In the last decades of the twentieth century numerous catalytic systems have been developed for this transformation. While some advances have been obtained, all suffer from either low catalyst stability/reactivity, the need for co-solvent, or the requirement for high pressure and/or catalyst costing expensive.[4] Therefore, to find an effective,not exrensive, environmentally benign economic catalyst system is urgent.In this paper, chemical fixation of CO2 with mono-substituted terminal epoxides or cyclohexene oxide to form cyclic carbonates under the ZnCl2/[BMIm]Br Catalyst System without using additional organic solvents was achieved in excellent selectivity (＞98%) TOF(5410h-1) Besides,the pure cis-cyclic carbonate of cyclohexene oxide was obtained in this catalyst system.It was important to note that the catalyst could be recovered by simple vacuum distillation of the corresponding cyclic carbonates could be used six times almost without losing its catalytic activity selectivity. The catalyst system was found to be applicable to a variety of terminal epoxides cyclohexene oxide, forming the corresponding cyclic carbonates in very high TOF more than 98% selectivity. Based on the obtained results, we also propose the plausible mechanism for this chemical fixation reaction of CO2.