Study of Superbase-Based Deep Eutectic Solvents as the Catalyst in the Chemical Fixation of CO2 into Cyclic Carbonates under Mild Conditions

Superbases have shown high performance as catalysts in the chemical fixation of CO₂ to epoxides. The proposed reaction mechanism typically assumes the formation of a superbase, the CO₂ adduct as the intermediate, most likely because of the well-known affinity between superbases and CO₂, i.e., superbases have actually proven quite effective for CO₂ absorption. In this latter use, concerns about the chemical stability upon successive absorption-desorption cycles also merits attention when using superbases as catalysts. In this work, ¹H NMR spectroscopy was used to get further insights about (1) whether a superbase, the CO₂ adduct, is formed as an intermediate and (2) the chemical stability of the catalyst after reaction. For this purpose, we proposed as a model system the chemical fixation of CO₂ to epichlorohydrin (EP) using a deep eutectic solvent (DES) composed of a superbase, e.g., 2,3,4,6,7,8-hexahydro-1