A Simple Halide-to-Anion Exchange Method for Heteroaromatic Salts and Ionic Liquids

Abstract: A broad and simple method permitted halide ions in quaternary heteroaromatic and ammonium salts to be exchanged for a variety of anions using an anion exchange resin (A⁻ form) in non-aqueous media. The anion loading of the AER (OH⁻ form) was examined using two different anion sources, acids or ammonium salts, and changing the polarity of the solvents. The AER (A⁻ form) method in organic solvents was then applied to several quaternary heteroaromatic salts and ILs, and the anion exchange proceeded in excellent to quantitative yields, concomitantly removing halide impurities. Relying on the hydrophobicity of the targeted ion pair for the counteranion swap, organic solvents with variable polarity were used, such as CH₃OH, CH₃CN and the dipolar nonhydroxylic solvent mixture CH₃CN:CH₂Cl₂ (3:7) and the anion exchange was equally successful with both lipophilic cations and anions.