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E-Journal of Chemistry
Volume 2, Issue 1, Pages 75-85

Mechanism of Oxidation of L-Histidine by Heptavalent Manganese in Alkaline Medium

Timy P. Jose,1 Sharanappa T. Nandibewoor,2 and Suresh M. Tuwar1

1Department of Chemistry, Karnatak Science College, Dharwad-580001, India
2Postgraduate Department of Studies in Chemistry, Karnatak University, Dharwad-580003, India

Received 6 November 2004; Accepted 14 December 2004

Copyright © 2005 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The kinetics of oxidation of L-histidine by manganese(VII) in aqueous alkaline medium at a constant ionic strength of 0.05 mol dm-3 was studied spectrophotometrically. The reaction between permanganate and L-histidine in alkaline medium exhibits 2:1 stoichiometry (KMnO4: L-histidine). The reaction is of first order in [KMnO4], less than unit order in [L-histidine] and [alkali]. Decrease in the dielectric constant of the medium decreases the rate of reaction. Effect of added products and ionic strength of the reaction medium have been investigated. The main products were identified by spot test and I.R. A mechanism involving the free radical has been proposed. In composite equilibrium step L-histidine binds to MnO4- species to form a complex(C). The reaction constants involved in the different steps of mechanism are evaluated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities are also determined.