Imidazolium-based deep eutectic solvents as multifunctional catalysts for multisite synergistic activation of epoxides and ambient synthesis of cyclic carbonates

Abstract

Novel imidazolium-based deep eutectic solvents were facilely synthesized and characterized by TGA, DSC, FT-IR, and NMR techniques. Various imidazolium salts and aromatic compounds containing active hydrogens were applied as HBAs and HBDs respectively for efficient cycloaddition of CO2 with styrene oxide under ambient conditions. The optimized [C1C2Im]I/m-DHB (1-ethyl-3-methylimidazolium iodide/m-dihydroxybenzene) DES with the molar ratio of 2:1 exhibited excellent catalytic activity at room temperature and 0.1 MPa CO2 pressure without cocatalyst, metal, and solvent. Moreover, the effects of reaction parameters, substrate scope, and catalyst recovery were studied in detail. Based on the results, the plausible reaction mechanism on the multisite synergistic activation of the epoxide by the hydrogen bonds involved with both the OH in m-DHB and C2-H in [C1C2Im]I was proposed. Finally, the reaction kinetics was studied and the cycloaddition reaction was accorded with the pseudo-first-order reaction kinetic model.