Dithizone adsorption at matal electodes. Electrochemical characterization of dithizone anion at a silver electrode

The redox behavior of the anion of diphenylthiocarbazone (dithizone) has been investigated at a silver electrode in alkaline media. The dithizone anion is reduced at the azo group at silver, but the observed voltammetric wave is split into surface and bulk components due to the adsorption of the anion at the silver surface. The product of this electrode reaction, the correponding hydrazo species, is also adsorbed at silver surface, but to a lesser extent. The cathodic processes for the dithizone anion reduction are complicated in alkaline solutions prepared with alkali hydroxides by the electrodeposition of alkali metals onto the silver surface and the subsequent formation of alkali metal-silver intermetallic compounds. The dithizone anion can also be oxidized at silver to form the corresponding disulfide compound. This disulfide, which is insoluble in the aqueous systems, adsorbs at the silver surface in multilayer quantities. This disulfide film passivates the silver electrode towards surface oxidation until potentials >ca. 400-500 mV (vs. Ag/AgCl) are reached.