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(CF,CF3)(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 H-1 NMR spectra using the intensity of the C-13 satellites of the imidazolium N-methyl group as internal standard.