C16 TAB catalyzed oxidative decolorisation of methylene blue by acidic N-chloro-p-toluenesulfonamide

Abstract

Kinetics and mechanism of uncatalyzed and C 16 TAB catalyzed oxidation of methylene blue (phenothiazin-5-inum, 3,7-(dimethyl amino)-chloride) [MB + ] by N-chloro-p-toluenesulfonamide in acidic media has been studied spectrophotometrically. With excess concentrations of other reactants, the reaction rate follows pseudo-first order kinetics with respect to methylene blue. The uncatalyzed reaction has fractional order dependence on chloramine-T and zero order dependence on H + concentration (in the range 1.0 x 10 -2 M to 9.0 × 10- 2 M). Cationic surfactant cetyl trimethyl ammonium bromide catalyzes the reaction eveh before its CMC. A bathochromic shiff is the evidence of dye-surfactant interaction. The premicellar kinetics has been rationalized in the light of Piskiewicz positive co-operativity. Positive cooperativity index (n = 1.27) has been computed. Variations of ionic strength have no influence on the reaction rate. The basic stoichiometry equation is as follows: MB + + 2CAT + 2H 2 O = P 2 + + 2CH 3 C 6 H 4 SO 2 NH 2 + 2NaCl + 2HCHO where, P 2 + = 4aH-phenothiazine-3,7-diamine 5-oxide. On the basis of product analysis a pertinent mechanism is proposed.