Potentiometric studies on electrolytically generated manganese(III) acetate in aqueous acetic acid: Oxidation of thiosemicarbazide, its metal complexes and thiosemicarbazones

Abstract

Conditions for generating manganese (lll) acetate electrochemically with high current efficiency have been determined in aqueous acetic acid solutions. Nature of the manganese species formed has been elucidated spectro-photometrically. Conditions for potentiometric determination of thiosemicarbazide (TSC), its metal complexes and thiosemicarbazones have been investigated. Thiosemicarbazide has been found to undergo four electron oxidation whereas its metal complexes M(TSC)₂SO₄' participate in eight electron redox process, indicative of the number of TSC-ligands present in the complexes. All the thiosemicarbazones with the exception of salicylaldehyde thiosemicarbazone, undergo four electron redox process with the regeneration of the respective aldehydes. Salicylaldehyde thiosemicarbazone reacts in two stages namely four electron oxidation of thiosemicarbazone with the regeneration of salicylaldehyde which is further oxidised at elevated temperature to salicylicacid. The formal redox potentials of Mn(lll)-Mn(II)couple at various percentages (v/v) of acetic acid and.in the presence of anions CH₃COO^-, Cl^-, F^-, ClO₄ have been determined and compared with the earlier work involving manganic sulphate in H₂SO₄-HOAc medium. The reactive species envisaged in the present system are the undecomposed manganese(lll) acetate or the complex, Mn(OAc),while the earlier system contains free aquo manganic ions, Mn³⁺ aq. or MnOH²⁺ aq. as evident from spectral and redox potential values.