A process where ionic liquids catalyze the cycloaddition of carbon dioxide to propylene oxide

Abstract

Experiments on the cycloaddition of carbon dioxide to propylene oxide at room temperature ionic liquids based on 1-n-butyl-3-
methylimidazolium and n-butylpyridinium salts have been conducted, all without the need of additional organic solvents. The most active
catalyst, with about 100% selectivity, was determined to be 1-n-butyl-3-methylimidazolium tetrafluoroborate. A high conversion rate required
an appropriate molar ratio of CO to propylene oxide. The catalyst for the process, an ionic liquid, may be recycled. Five-membered cyclic
carbonates are excellent aprotic polar solvents and are used extensively as intermediates in the production of drugs and pesticides. The
formation of cyclic carbonates via cycloaddition of epoxides and carbon dioxide, which is one of the routes for carbon dioxide chemical
fixation,1 has received much attention as regards the utilization of carbon resources and the reduction of CO pollution.
Cycloaddition between epoxides and carbon dioxide using organic and inorganic compounds such as metal halides,2,3 onium halides, metal
complexes4h6 and MgO,7 MgÈAl mixed oxides,8 KIÈZnO,9 etc. as catalysts generally occur at low rates unless high temperature, high
carbon dioxide pressure, long reaction time and/or high catalyst/substrate ratios are used. More recently, propylene carbonate has also been
syn- thesized from supercritical carbon dioxide (sc-CO )Èpropylene oxide mixture with phthalocyaninatoaluminium chlorideÈ
tetrabutylammonium bromide as catalyst, which necessitates a