Stability of 10-acetylphenothiazine.

The degradation kinetics of 10-acetylphenothiazine were studied after isolation and identification of its degradation products, phenothiazine, phenothiazine-5-oxide, 3H-phenothiazine-3-one, and 7-(10'-phenothiazinyl)-3H-phenothiazine-3-one. The acetyl group was not present in any degradation product. The degradation rate was independent of oxygen but highly pH dependent, indicating a specific hydrogen-ion-catalyzed hydrolysis of 10-acetylphenothiazine to give phenothiazine, which was oxidized. The experimental values for the phenothiazine concentration were in good agreement with values calculated on the basis of this assumption, both in the presence and absence of oxygen.