Cu(I)-containing room temperature ionic liquids as selective and reversible absorbents for propyne

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 pi-complexation of propylene and propyne with Cu in Cu-RTIL is not observed.