Identification of intermediate compounds and photodegradation mechanisms of omeprazole under the system UV/O-2

Abstract

The photodegradation of the proton pump inhibitor omeprazole (OME) in aqueous media with the system UV/O2 is presented. The photodegradation rate was assessed by HPLC and UV‐vis spectroscopy, while the mineralization rate was obtained by TOC measurements. Degradation products were investigated by IR spectroscopy and GC‐MS analysis. UV‐vis absorbance and HPLC results indicated that OME is completely degraded within 3 minutes of irradiation. TOC analysis indicated that intermediates compounds are relatively easy to mineralize since 80% mineralization is achieved within 2 hours. IR studies demonstrated a rapid oxidation of OME leading to the formation of amines and both sulfonic and carboxylic acids. GC‐MS data indicated that the initial photoproducts are derivatives of both benzimidazole and pyridine produced after the photochemical cleavage of the C–S bond. Plausible mechanisms for the direct and indirect degradation of OME are given. In the photochemical degradation of OME, many intermediate compounds are actually generated. Several of them were generated from hydroxyl radical reactions, but some of them resulted from rearrangements, reductive reactions, and through the formation of highly reactive intermediates such as pseudo carbene, thiooxirane, and sulfenamide.