A Specific Synergistic Effect in Ionic Liquid Chelate Extraction Based on Neutral Ternary Chloro-complex Formation

In the chelate extraction of zinc(II) into an ionic liquid (IL), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C4mimTf2N), with 8-(p-toluenesulfonamido)quinoline (Htsq), the co-existence of a certain amount of chloride anion in the aqueous phase resulted in an enhancement of the extractability. This enhancement did not occur at all in that into chloroform, a conventional organic extraction solvent. The specific synergistic effect was based on the dominant extraction of a neutral ternary complex, Zn(tsq)Cl, which is unstable in molecular organic solvents.