1-Butyl-2,3-trimethyleneimidazolium bis(trifluoromethylsulfonyl)imide ([b-3C-im][NTf 2]): a new, stable ionic liquid

Abstract

Using imidazole as the starting material, the synthesis of a new bicyclic ionic liquid [b-3C-im][NTf 2] is described. Except for the alkylation reaction in the second step (40% yield) of this four-step synthesis of [b-3C-im][NTf 2], others were all high yielding reactions (85–94% isolated yields). We investigated intrinsic reactivity of this and other imidazolium-based ionic liquids and found that, under strongly basic conditions (KOD in CD 3OD/D 2O (1:1) solution), the new ionic liquid was stable to solvent deuterium isotope exchange while the previously reported [bdmim][NTf 2] and [bdmim][PF 6] ionic liquids were 50% deuterium exchanged at its C-2 methyl in 30 min at ambient temperature. At the same experimental condition, the most commonly employed [bmim][PF 6] ionic liquid was deuterium exchanged instantaneously at its C-2 hydrogen. In the absence of bases (CD 3OD/D 2O = 1:1), only [bmim][PF 6] was deuterium exchanged (50% within 1 h) and other ionic liquids gave no detectable exchanges even after one week at ambient temperature. It is therefore concluded that the new [b-3C-im][NTf 2] ionic liquid is far more chemically stable than previously reported [bmim][PF 6], [bdmim][NTf 2], and [bdmim][PF 6].