New hydrogen carbonate precursors for efficient and byproduct-free syntheses of ionic liquids based on 1,2,3-trimethylimidazolium and N,N-dimethylpyrrolidinium cores

Two new hydrogen carbonate IL precursors, 1,2,3-trimethylimidazolium and N,N-dimethylpyrrolidinium hydrogen carbonate salts, were synthesized and their structures confirmed by NMR and single-crystal X-ray diffraction. These salts were also evaluated for application in the syntheses of ILs by reacting them with a variety of acids and [NH4][ClO4], which resulted in the clean and quantitative formation of a family of 1,2,3-trimethylimidazolium- and N, N-dimethylpyrrolidinium-based salts. Synthetic protocols for the formation of the hydrogen carbonate salts involved simple alkylation reactions of the chosen neutral amines with dimethyl carbonate, and later conversion of the formed methyl carbonate anion-based salts to hydrogen carbonate salts. The reactions proceed in one step at temperatures close to room temperature using only water. The new organic salts with the chosen anions are formed with only gaseous byproducts (CO2, H2O, and in the case of [NH4][ClO4], NH3), thus eliminating further purification steps. This generalized synthetic protocol for the formation of hydrogen carbonate IL precursors may be used as a cleaner, contaminant-free (halides and metal ions) route to many classes of ILs.