Systematic Study on the General Preparation of Ionic Liquids with High Purity via Hydroxide Intermediates

High-purity ionic liquids were prepared from halide precursors by an optimized synthesis route. This preparation route consisted of three steps, i.e. methathesis, ion exchange, and acid/base neutralization. A significant amount of halide impurity remained in the ionic liquids. Metal and halide impurities were effectively removed by utilizing an ionic exchange column. Multiple parameters that affected the amounts of impurities in the final product, such as molar ratio of halide precursor to potassium hydroxide, amount of ethanol solvent, type of resin, and concentration of hydroxide, were investigated in detail. Two high-purity hydroxide intermediates ((N2221)OH and (C6mim)OH) were prepared by metathesis and ion exchange, and they were then neutralized with four different acids to produce a series of ionic liquids. The yields of cations and anions in the ionic liquids as well as the concentrations of impurities in each step were determined to verify the feasibility of the method. The new preparation route is of great potential in preparing various high-purity ionic liquids.