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.
The distribution constants of 4-benzoyl-3-phenyl-5-isoxazolone (HPBI) and deprotonated one (PBI) between hydrophobic ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([CCim][TfN]) and aqueous phases were determined, together with the acid-dissociation constant of HPBI. The solvent extraction of three selected lanthanoid ions (La, Eu, and Lu) with HPBI from aqueous nitrate phase into [CCim][TfN] has been investigated. Application of the ionic liquid as the extracting phase greatly enhanced the extraction performance of HPBI for lanthanoid ions compared with that in the chloroform system. A slope analysis was conducted in order to compare the results of the solution 4f-ion coordination chemistry in ionic and molecular media. The composition of the extracted species was established to be anionic tetrakis entities, Ln(PBI), for light, middle, and heavy lanthanoid ions in an ionic environment (Ln denotes lanthanoid ion). Nevertheless, the typical neutral chelate lanthanoid complexes of the type Ln(PBI) have been detected when the conventional molecular diluent chloroform was applied as an organic phase.
The three ILs (C2mimTf2N, C4mimTf2N and C8mimTf2N) were synthesized according to a reported procedure. 47,48 The extraction reagent HQ was purchased from FUJIFILM Wako Pure Chemical Corporation (Osaka, Japan). Other chemicals and solvents included reagent-grade materials, which were used without further purification. High-purity water was produced with a Millipore Direct-Q water-purification system.
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