We report experiments on the extraction of acids and bases from an aqueous phase to a pseudoprotic ionic liquid phase consisting of an equimolar mixture of trihexylamine and octanoic acid. We observed the extraction of a wide range of acids and bases, and investigated the mechanism of extraction in detail. Our results confirmed the observation of the Hofmeister effect in these systems reported in our previous work, where the extent of the extraction of copper salts was significantly influenced by the interactions between extracted inorganic anions and the organic phase. Our results further demonstrated that the organic layer served as a "floating buffer" capable of stabilizing the pH of an acidic or alkaline aqueous phase. The results tie current interest in protic and pseudoprotic ionic liquids to earlier work on the extraction of acids using amine and acid⁻base couples as extraction agents in an inert organic solvent.
Keywords: Hofmeister effect; acid extraction; protic ionic liquids.