Kinetics and mechanism of C16TAB catalyzed oxidation of methylene violet by chloramine-T in acidic medium

Abstract

Kinetics and mechanism of uncatalyzed and C16TAB catalyzed oxidation of methylene violet (3-amino-7-(diethyamino)-5-phenyl phenazinium chloride) (MV+) by chloramine-T in acidic media has been kinetically studied using spectrophotometry. With excess concentrations of other reactants, the reaction rate follows pseudo-first order kinetics with respect to methylene violet. The uncatalyzed reaction has first order dependence on chloramine-T and zero order dependence on H+ concentrations (in the range 1.0×10^-2 to 6.0×10^-2 M). The reaction is catalyzed by cetyltrimethyl ammonium bromide, a cationic surfactant, even before the cmc. A bathochromic shift is the evidence of dye-surfactant interaction. The pre-micellar kinetics has been rationalized in the light of Piszpiwicz positive co-operativity. Positive cooperatively index (n = 2.7) has been computed. The order in [Cl-] is unity. Variation of ionic strength and the initial addition of p-toluenesulphonamide have no influence on the reaction rate. The rate of depletion of the dye decreases with the increase in pH from 2 to 6. On the basis of product analysis a pertinent mechanism is proposed.