Distribution Equilibria of Amphoteric 8-Quinolinol between 1-Alkyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imide and Aqueous Phases and Their Effect on Ionic Liquid Chelate Extraction Behavior of Iron(III)

: The distribution behavior of amphoteric 8-quinolinol (HQ) between ionic liquid (IL) phase and aqueous phase and ionic liquid chelate extraction behavior of iron(III) with HQ were investigated using four 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (CnmimTf2N, n = 2, 4, 6 and 8) ILs. Not only neutral HQ but also cationic H2Q+ were distributed into the IL phase, and the latter distribution based on cation-exchange with Cnmim+ was pronounced in the use of IL having a less-hydrophobic cation, such as C2mim+. In the IL chelate extraction of iron(III), the extractability increased with the increase in the hydrophobicity of IL as the extraction phase. Nevertheless, the determined equilibrium constants for the extraction as the neutral complex FeQ3 were similar to one another. The difference in the extractability among the ILs was due to the difference in the distribution of H2Q+ into the extraction phase. In addition, the cationic coordinatively-unsaturated complex FeQ2+ was also extracted in use of less-hydrophobic C2mimTf2N.