Ionic liquid-assisted carboxylation of amines by CO2: a mechanistic consideration

Abstract

The catalytic roles of ionic liquids (ILs) in the syntheses of 1,3-disubstituted ureas from the carboxylation of amines by CO₂ were experimentally and theoretically investigated. The carboxylation reaction of n-butylamine was greatly facilitated by the presence of an IL and the catalytic activity of the IL was strongly affected by the nucleophilicity of the anion. Computational study on the mechanistic aspects of the carboxylation with methylamine with or without the presence of an IL, 1-ethyl-3-methylimidazolium chloride, implies that the activation energies of the transition states and the intermediate ionic species could be lowered significantly through the multi-interactions of the carbonyl group of CO₂ with both cations and anions of the ILs.