Acidic pyridinium ionic liquid: an efficient bifunctional organocatalyst to synthesis carbonate from atmospheric CO2 and epoxide.

Ionic liquids (ILs) are used as non-toxic, biodegradable, non-volatile, and relatively low-cost catalysts to synthesize 5-membered cyclic organic carbonates (COCs) from carbon dioxide (CO2) and different types of oxiranes in great conversion and selectivity. Single-component IL containing pyridinium salt moieties as quaternary amine, the carboxylic functional group as a H-bond donor, and bromine as a nucleophile and significant leaving group was synthesized by a simple method. The simultaneous selection and use of all mentioned factors in IL caused the epoxides converted into their corresponding carbonates under mild conditions, under 1 atm carbon dioxide (CO2) pressure (CO2 balloon), co-catalyst/ metal/ and solvent-free during 2.5 h. The synthetic catalyst converted styrene oxide (SO) to styrene carbonate (SC) with 100% conversion and selectivity. Moreover, the catalyst could be recycled more than four times before losing its remarkable catalytic activity. Finally, an inferential mechanism was suggested according to the experimental results.