Chitosan functionalized ionic liquid as a recyclable biopolymer-supported catalyst for cycloaddition of CO₂

Development of efficient, cheap and recyclable catalysts for a reaction under green reaction conditions is still a very attractive topic. In this work, the cycloaddition reactions of CO₂ with various epoxides to form five-membered cyclic carbonates catalyzed by chitosan functionalized 1-ethyl-3-methyl imidazolium halides (CS-EMImX, X = Cl, Br) without additional solvent and metal co-catalyst were achieved in high yield and selectivity. The catalyst could be easily recovered and reused five times with high catalytic activity and selectivity. Besides, a possible catalytic cycle for the hydrogen bond assisted ring-opening of epoxide and activation of CO₂ induced by the nucleophilic tertiary nitrogen of the chitosan was also proposed. The process represents a simple, ecologically safe and cost-effective route to synthesize cyclic carbonates with high product yield, as well as easy catalyst recycling.