Kinetics and Mechanisms of the Non-Catalyzed and Manganese(II) Catalyzed Oxidation of Neutral Red with Potassium Periodate in Aqueous Solution

Abstract

A detailed kinetic and spectrophotometric investigation has been made for the oxidation of neutral red, a cationic phenazine dye, using potassium periodate in aqueous media. The rate of the oxidation reaction attained a first order dependence on the dye and the oxidant only at lower concentrations of the latter. The rate of reaction increases with increasing pH of the medium due to the deprotonation of the substrate nitrogen atoms. Moreover, the rate of reaction decreases with increasing ionic strength of the medium, suggesting an interaction between two singly oppositely charged ions in the activated complex. However, addition of trace amounts of manganese(II) ions sharply increases the oxidation rate. Mechanisms are proposed for both the non-catalyzed and manganese(II) catalyzed reactions which are in agreement with the experimental data.