Potentiometric Studies on Electron Transfer Reactions of Anodically generated Manganese(III) Sulphate in Aqueous H2SO4-HOAc and Manganese(III) Acetate in Aqueous Acetic Acid : Oxidation of Semicarbazide and Semicarbazones

St. Aloysius College, Mangalore-575 003

Department of Chemistry, Mangalore University, Mangalagangothri-574 199

NGSM Institute of Pharmaceutical Sciences, Derlakatte, Mangalore

Chemical Engineering Departmenl, MIT, Manipal-576 119
Manuscript received 22 May 1992, revised 27 April 1994. accepted 28 June 1994

Manganese( Ill) sulphate in aqueous sulphuric add and manganese(III) acetate in aqueous acetic acid have been prepared by electrolytic methods with high current efficiency. The nature of the manganese( Ill) formed is elucidated spectrophotometrically. Condition for potentiometric determination of semicarbazide and its derivatives under different reaction conditions have been  investigated. Hydrazinium sulphate or hydroquinone is employed as back-titrant. The number of electrons in these oxidations differed, depending on the nature of the molecule and the reaction condition. The free radical nature of the reaction intermediate is demonstrated. Manganese(III) sulphate and manganese(lll) acetate oxidation of Semicarbazide and its derivatives in aqueous H₂SO₄ or aqueous HOAc yielded different results, probably because of the changes in the coordination lnvironment or manganese(III).