Conditions have been established for the electrogeneration of Mn III from MnII in a sulphuric acid medium. The Mn III formed was identified and characterized by ultraviolet spectra. The stability of standard solutions of manganese(III) sulphate at various concentrations of H+, MnII and acetic acid and in the presence of the complexing agents P2O74-, Cl- and F- was studied and conditions for the potentiometric determination of thiosemicarbazide (TSC), its metal complexes, M(TSC)2SO4, and its thiosemicarbazone derivatives, propanal thiosemicarbazone (PTSC) and benzaldehyde thiosemicarbazone (BTSC), have been investigated. Thiosemicarbazide in H2SO4 underwent a six-electron oxidation. The M(TSC)2SO4 complex participates in a 12-electron redox process, indicative of the number of TSC ligands present in the complex. The PTSC in an H2SO4-HOAc (20% v/v) medium underwent oxidation in two stages, namely, six-electron oxidation of TSC with the regeneration of propionaldehyde and two-electron oxidation of the aldehyde to the corresponding carboxylic acid. The benzaldehyde regenerated from BTSC did not undergo further oxidation. Above 40% HOAc, a reproducible four-electron stoichiometry was achieved thereby showing the selectivity of MnIII as an oxidizing agent. The formal redox potential of the MnIII-MnII couple with and without the complexing agents and at various concentrations of H+ was determined. Addition of complexing agents decreased the formal redox potential of the MnIII-MnII couple, thereby reducing the oxidation rate, but did not alter the over-all stoichiometry of the electron transfer process.
All Science Journal Classification (ASJC) codes
- Analytical Chemistry
- Environmental Chemistry