Polarographic Oxidation and Reduction of O-Ethyl Thioacetothioacetato Complexes of Zinc(II), Cadmium(II), and Mercury(II) in Acetone

Polarographic oxidation and reduction of complexes of O-ethyl thioacetothioacetate (OEt-SacSacH) with ndw ions have been examined at the dme in acetone-0.1 M Et₄NClO₄. Coulometry has defined the oxidation of Zn(OEt-SacSac)₂ as a four-electron step which is believed to yield Zn(II) and the 3-methyl-5-ethoxy-1,2-dithiolium ion: Zn(OEt-SacSac)₂ → Zn(II) + 2[OEt-SacSac]⁺ + 4e^-. The oxidation has also been achieved chemically using iodine as an oxidant. Cd(OEt-SacSac)2 exhibits similar behavior to Zn(OEt-SacSac₎₂. With Hg(OEt-SacSac)₂, however, the oxidation is believed to occur via the electrode process Hg(OEt-SacSac)₂ + Hg → 2[Hg-(OEt-SacSac)]⁺ + 2e^-. On reduction the zinc and cadmium complexes undergo consecutive one-electron reduction steps and mercury a single two-electron reduction with an associated prewave. The zinc complex is reduced reversibly to the [Zn(OEt-SacSac)₂]^- and [Zn(OEt-SacSac)₂]^2- species, although the reduced zinc complex exhibits only a short lifetime. Inverse voltammetry at a hanging drop mercury electrode for the Cd(II) and Zn(II) complexes reveals that the products of the reduction are not amalgams. Ac polarograms have been obtained and substantiate the dc findings on the reversibility or otherwise of the electrode processes.