Effect of cationic micelles of cetytrimethylammonium bromide on the oxidation of thiourea by permanganate

Kinetics of MnO4−-thiourea redox reaction have been investigated spectrophotometrically in presence of cationic micelles of cetyltrimethylammonium bromide (CTAB). Upon mixing aqueous solutions of permanganate and thiourea, a readily distinguishable brown colour appears and then disappears slowly. Various experiments have been performed to confirm the nature of brown colored solution. The effects of [MnO4−], [thiourea] and [H+] on the reaction rate were determined in presence of CTAB (=8.0 × 10−4 mol dm−3). Absorbance of the reaction mixture increases with [CTAB] which suggest the incorporation/association of permanganate with the head group of CTAB micelles. Menger–Portnoy model was used to explain the effect of CTAB micelles. The reaction proceeds through the fast formation and slow decomposition of water-soluble colloidal MnO2 as an intermediate. A suitable mechanism is proposed for the oxidation of thiourea by permanganate.