Can any Basic/Nucleophile Quaternary Salt Promote the Carbonatation of Epoxides? A Review

This review examines the role of ionic liquids (ILs) in the catalytic carbonation of epoxides for the synthesis of cyclic carbonates, focusing on the key factors that influence reaction efficiency. The nucleophilicity and basicity of the anions in IL catalysts are highlighted as critical components for promoting the cycloaddition reaction with CO₂. The solubility and ionicity of the ILs also significantly affect the reaction, with higher ionicity leading to better solubilization and catalytic performance. Additionally, the review emphasizes the importance of the water content in influencing solvation and the generation of nucleophilic species, particularly in hydrophilic IL environments. Mechanistic studies, supported by density functional theory (DFT) calculations, provide insight into the reaction pathways, although more detailed kinetic data are required. The induction period observed in some reactions suggests the formation of ionic nucleophilic species, but it is still premature to draw definitive conclusions regarding the effects of various reaction parameters. The review calls for further exploration of the kinetic data and competitive experiments to fully understand the role of ILs in epoxide carbonation.