Studies of the effect of IL cation / anion hydrophobicity and the nature of the aqueous phase anion on the extraction of alkali and alkaline earth cations from an acidic aqueous phase into 1,3-dialkylimidazolium-based and quaternary ammonium-based ILs by crown ethers have revealed significant similarities between the behavior of the two IL families. To further explore the “generic” nature of these observations and their potential application in the rational design of ILs for use as extraction solvents, the extraction of several metal ions (Na+, Sr2+ and Ba2+) from nitric and hydrochloric acid solutions by dicyclohexano-18-crown-6 into a series of N-alkylpyridinium-based ILs has been studied. Although much of the metal ion extraction behavior observed in these systems is consistent with that seen previously for the 1,3-dialkylimidazolium and quaternary ammonium-based ILs, certain observations, such as the effect of IL cation hydrophobicity on Sr2+ extraction from HNO3 by N-alkylpyridinium-ILs bearing long (dodecyl- and tetradecyl-) alkyl chains, cannot be fully explained by the established three-path model for metal ion partitioning. Instead a complete description of metal ion extraction in these systems appears to require consideration of the aggregation of the IL cation in the aqueous phase.

Factors influencing the mode(s) of metal ion partitioning into N-alkylpyridinium-based ionic liquids (ILs)

249th National Meeting (2015)

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