ABSTRACT
The catalytic roles of ionic liquids (ILs) in the syntheses of 1,3-disubstituted ureas from the carboxylation of amines by CO(2) 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 CO(2) with both cations and anions of the ILs.
ABSTRACT
A Cu(i)-containing room temperature ionic liquid (Cu-RTIL), prepared from CuCl and 1,3-dimethylimidazolium methylphosphite ([DMIM][MeHPO(3)]), was found to reversibly and selectively interact with propyne over propylene. Cu-RTIL exhibited 12 times higher propyne absorption capacity and 14 times higher ideal propyne/propylene selectivity than [DMIM][MeHPO(3)]. Fast atom bombardment (FAB)-mass spectral and computational results with Cu-RTIL (CuCl/[DMIM][MeHPO(3)] = 1/2) strongly imply that the Cu-RTIL contains stable methylphosphite-coordinated anionic Cu(i) species such as CuCl(MeHPO(3))(-) and Cu(MeHPO(3))(2)(-). Computational studies on the optimized structures demonstrate that the preferential absorption of propyne over propylene in a Cu-RTIL originates from the difference in the interaction mode between the coordinated phosphite ligand and propyne or propylene. Strong π-complexation of propylene and propyne with Cu in Cu-RTIL is not observed.
