Synergistic effect of a binary ionic liquid/base catalytic system for efficient conversion of epoxide and carbon dioxide into cyclic carbonates

Abstract

Carbon dioxide (CO2) mitigation via utilization can be a potential solution to global warming issues such as increasing CO2 concentration. In this study, we present the synthesis and characterisation of 3-(2-hydroxyethyl)-1-vinyl-1H-imidazol-3-ium chloride [EvimOH][Cl] and 3-(2-hydroxyethyl)-1-vinyl-1H-imidazol-3-ium sulphate [EvimOH][HSO4] ionic liquids for cycloaddition reactions of CO2 and epoxides into cyclic carbonates. The synthesized ionic liquids were characterized by FT-IR, 1H- and 13C-NMR spectroscopic methods. Also, we have analysed the physical properties of ionic liquids by using TGA and DTA. Further, the CO2 consumption was done by developing a binary catalytic system with bases such as DBU, TEA, DIPEA, piperidine, pyrrolidine, aniline. The developed binary ([EvimOH][Cl]/base) catalytic system exhibited the excellent catalytic activity of 99.8% conversion and ≥99% selectivity under mild reaction conditions without the aid of solvent and metal co-catalysts. Furthermore, the results show that the improved activity from the binary system is due to synergistic effect among −OH functional group from the cation, reactive acidic C(2)-H in the imidazolium ring and amine containing bases which promote the CO2 absorption. Also, a plausible mechanism of cyclic carbonate formation and kinetic study in the presence of binary catalytic system was demonstrated.