Coupled Ion Complexation and Exchange between Aqueous and Ionic Liquid Phases: A Thermodynamic Interpretation

Experimental studies of ion extraction from aqueous to ionic liquid phases have demonstrated that, in many cases, extraction of an ion from the aqueous phase is coupled to counterextraction of similarly charged ions from the ionic phase. These exchanges often involve coordination complexes that are not observed in extractions from aqueous phases to molecular organic liquids. We make a thermodynamic analysis of this coupled ionization/exchange process, and show that it is driven by the relative solubilities of the ionic liquid ion and the complex in the two phases. We apply the analysis to a series of systems for which the phenomenon has been documented, and discuss general principles that can be used to control the process.