Synthesis of cyclic carbonates from epoxides and carbon dioxide over silica-supported quaternary ammonium salts under supercritical conditions

A silica-supported quaternary ammonium salt is reported for the first time as a recyclable and efficient catalyst for the synthesis of propylene carbonate from propylene oxide and carbon dioxide under supercritical conditions, which requires no additional organic solvents either for the reaction or for the separation of product. Moreover, the catalyst can be easily recovered by a simple filtration and reused over four times without obvious loss of its catalytic activity. The effects of the types of cation and anion of quaternary ammonium salts, and other reaction parameters on the reaction are investigated. This organic solvent-free process presented here could show much potential application in industry due to its simplicity, easy product separation from reaction medium and catalyst recycling. It could be profitably applied to the development of fix-bed continuous flow reactors, avoiding the use of solvent to isolate the products. (c) 2006 Elsevier B.V. All rights reserved.