勝田 正一

Effect of phenols as organic proton donors on the chelate extraction of metal ions was thoroughly investigated. A remarkable enhancement of extractability was found in the solvent extraction of various metal ions (Be(II), Sc(III), Fe(III), Cu(II), Zn(II), etc.) with typical chelating extractants (beta-diketones and 8-quinolinols) in the presence of halogenated phenols. This effect was ascribed to the association of neutral metal chelates (MA(m)) with the phenols (ArOH) in the organic phase. Spectroscopic measurements such as Nh IR indicated the existence of hydrogen bonds between MA(m) and ArOH. From analysis of the extraction equilibria, compositions of the association complexes were found to be MA(m).nArOH (n=1, 2 when m=2; n=1 similar to 3 when m=3), and their association constants and thermodynamic parameters were determined. Factors influencing the association equilibrium were systematically discussed with respect to the central metal ion, chelating reagent, phenol and solvent. The addition of phenols was also useful to improve selectivity of the chelate extraction. In this study, the remarkable role of hydrogen bonding in the chelate extraction was first clearly demonstrated and the characteristics of interaction between metal chelates and proton donors were elucidated.