A Simple and Practical Method for the Preparation and Purity Determination of Halide-Free Imidazolium Ionic Liquids

The reaction of N‐alkylimidazole with alkyl sulfonates at room temperature affords 1,3‐dialkylimidazolium alkanesulfonates as crystalline solids in high yields. The alkanesulfonate anions can be easily substituted by a series of other anions [BF4, PF6, PF3(CF2CF3)3, CF3SO3 and N(CF3SO2)2] by simple reaction of anions, salts, or acids in water at room temperature. Extraction with dichloromethane, filtration through a short basic alumina column and solvent evaporation affords the desired ionic liquids in 80–95% yield. The purity (>99.4%) of these ionic liquids can be determined by 1H NMR spectra using the intensity of the 13C satellites of the imidazolium N‐methyl group as internal standard.