Liquid—liquid extraction of transition metals with acylthioacetamides

The extraction behaviour of acylthioacetamides, R¹—CO—CH₂—CS—NR²R³, was studied for a series of transition metals. The highest distribution ratios were obtained with benzoylthioacetanilide. Complexes with acylthioacetamides which were completely substituted on the amide group were extracted slowly. The ranking of the extraction characteristics is related to the different pK_a values of the compounds used. Polymerization and solvation reactions can be excluded at metal concentrations of ? 10^-3 mol dm^-3 and extractant concentrations of ?10^-1 mol dm^-3, respectively. Decreasing extractability, Cu(II) > Zn(II) > Ni(II) > Co(II) > Cd(II), corresponds to the stability constants of the extracted metal chelates. Iron(III) cannot be extracted at pH ?3; Hg(II), Pd(II), and Au(III) are extracted readily over a reasonably wide pH range. The different extraction constants for zinc(II) and cadmium(II) permit an effective separation of these ions with benzoylthioacetanilide.