Oxidative degradation of pharmaceutically important phenothiazines I: Isolation and identification of oxidation products of promethazine.

The thermal degradation of promethazine in water in the presence of oxygen was studied. After degradation, the products were isolated by TLC. Identification was carried out by comparison of the isolated compounds with reference compounds. Melting points, spectral data, and polarographic and chromatographic behavior were compared. The following products were identified: 10-methylphenothiazine, phenothiazine, 3H-phenothiazine-3-one, phenothiazine 5-oxide, promethazine 5-oxide, 7-hydroxy-3H-phenothiazine-3-one, acetaldehyde, formaldehyde, and dimethylamine.