BCSJ : Vol. 78 (2005) , No. 7 pp.1218-1222

Kinetics of the MnO₄⁻ Oxidation of Anionic Surfactant (Sodiumdodecyl Sulphate): Evidence for the Formation of Soluble Colloidal MnO₂

Raju¹⁾ and Zaheer Khan¹⁾

1) Department of Chemistry, Jamia Millia Islamia, (Central University)

(Received July 20, 2004)

A conventional spectrophotometric technique was used to study the oxidation of SDS by permanganate in a perchloric acid medium. It was observed that the reaction proceeded in two stages (fast first stage followed by a relatively slow second stage). Plots of log(absorbance) versus time deviate from linearity. The kinetic and spectroscopic data are consistent with the formation of soluble colloidal MnO₂. The first-order kinetics with respect to [SDS] at low concentrations shifted to second-order at higher concentrations. The kinetics of oxidation is first-order with respect to both [MnO₄⁻] and [HClO₄]. The oxidation rate was decreased by the addition of P₂O₇⁴⁻ and Mn(II) ions. Second-step oxidation is not a true path for the oxidation of the Mn(IV)–SDS reaction. In the presence of Mn(II) (a reaction product), the MnO₄⁻ oxidation of SDS becomes more complicated, and an exact dependence on [Mn(II)] can not be estimated. Different activation parameters have been evaluated. Mechanisms consistent with the kinetic data have been proposed and discussed. The –O–SO₃⁻ group is responsible for the oxidative degradation of SDS by MnO₄⁻.