Oxidation kinetics of phenothiazine and 10-methylphenothiazine in acidic medium.

The rate of phenothiazine degradation in an acidic oxygen-saturated medium was studied. 3H-Phenothiazine-3-one and phenothiazine 5-oxide are produced by parallel reactions, and 7-(10'-phenothiazinyl)-3H-phenothiazine-3-one is produced in a more complex manner. The overall phenothiazine degradation rate appears to be pH independent up to pH 7.0. The degradation kinetics of 10-methylphenothiazine were studied after isolation and identification of its degradation products, 10-methylphenothiazine 5-oxide and 3H-phenothiazine-3-one. The main degradation product is 10-methylphenothiazine 5-oxide; but at low pH values and high temperatures, more 3H-phenothiazine-3-one is formed. The degradation rate of 10-methylphenothiazine is pH independent up to pH 7.