The development of efficient, inexpensive, and nontoxic catalysts for
cycloaddition of CO2 with epoxides to produce five-membered cyclic
carbonates is a very interesting topic. In this work, cycloaddition of
CO2 with propylene oxide (PO) to produce propylene carbonate (PC)
catalyzed by potassium halides (KCl, KBr, and KI) in the presence of
cucurbit[6]uril (CB[6]) was studied at various conditions. It was discovered
that the potassium halides and CB[6] had excellent synergetic effect in
promoting the reaction, and the KI/CB[6] catalytic system was the most efficient
among them. The decrease of the activity and selectivity of KI/CB[6] was
negligible after the catalytic system was reused five times. Further study
indicated that the KI/CB[6] catalytic system was also very active and selective
for the cycloaddition of CO2 with other epoxides, such as glycidyl
phenyl ether, epichlorohydrin, and styrene oxide. The mechanism for the
synergetic effect of KI and CB[6] was also discussed.