Ionic Liquid Chelate Extraction Behavior of Trivalent Group 13 Metals into 1-Alkyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imides Using 8-Quinolinol as Chelating Extractant

Ionic liquid (IL) chelate extraction behavior of trivalent Group 13 metals including aluminum(III), gallium(III) and indium(III) with 8-quinolinol (HQ) was investigated using three 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C_nmimTf₂N, n = 2, 4 and 8) ILs. Although the three extraction systems showed similar extraction selectivity among the metals, the extractability order for the metals among the extraction systems was C₈mimTf₂N > C₄mimTf₂N > C₂mimTf₂N, which was the same as the order of hydrophobicity in the IL cation. Only the neutral 1:3 complex species was extracted in use of more-hydrophobic C₈mimTf₂N, whereas use of less-hydrophobic C₄mimTf₂N and C₂mimTf₂N resulted in competitive extraction of neutral 1:3 and cationic 1:2 complexes. For each of the metals, in addition, similar extraction constants were obtained in these three extraction systems.