Reduction Kinetics of 3,7-bis (dimethylamino)-4-nitro-phenothiazine-5-ium Chloride (Methyelene Green) with Potassium Persufate in Presence of Halides

The effect of ionic strength and temperature on the kinetics of reaction between 3, 7 bis (dimethyl amino) - 4- nitro-phenothiazine-5-ium chloride (methylene green) and persulfate ions in presence of potassium iodide and potassium bromide was studied by spectrophotometric method. The overall reaction follows pseudo second order kinetics. First order with respect to persulfate and halide ions respectively and zero order kinetics with respect to Methylene green were observed. The reaction was studied at different ionic strengths and temperatures ranging from 25ºC to 50ºC. The kinetic data was evaluated in terms of Debye-Huckel-Bronsted (DHB) and Kilpatrick relations. It was observed that with the increase in ionic strength and temperature, the rate increases following DHB theory. The value of zAzB was also calculated from DHB plots and Kilpatrick plots. The effect of ionic strength on the activation parameters was also studied.