Selective removal of alkynes from diene mixtures using ether-functionalized Cu(i)-containing ionic liquids as extractants

Abstract

Cu(I)-Containing room temperature ionic liquids (Cu-E_nA), prepared from CuCl and ether-functionalized ionic liquids (ILs) bearing a methanesulfonate anion (E_nA, n = 1, 2 or 3), were thermally stable and highly effective for the removal of alkynes such as isopropenylacetylene (IPA) and 2-butyne (2-BT) contained in dienes like isoprene (2-methyl-1,3-butadiene). Cu-E_nA were found to reversibly and selectively interact with IPA and 2-BT, thereby enabling the regeneration of Cu-E_nA. Fast atom bombardment (FAB)-mass spectral and computational results imply that E_nA consists of an ether-functionalized imidazolium cation and a methanesulfonate-coordinated Cu(I) anion such as [CuCl(CH₃SO₃)]⁻ ([CuClA]⁻) or [Cu(CH₃SO₃)₂]⁻ ([CuA₂]⁻). Computational studies demonstrate that the preferential extraction of IPA and 2-BT to isoprene by Cu-E_nA originated from the difference in the strength of the hydrogen bonding and π-complexation.