A photochemical study of diclofenac and its major transformation products.

The photolytic transformation of 2-(2-(2,6-dichlorophenylamino)phenyl)acetic acid (diclofenac) and its transformation products (TPs) (8-chloro-9H-carbazol-1-yl) acetic acid (Cz1), 2-(2-chloro-phenylamino)-benzaldehyde (Ald) and (1,4-dioxo-4,9-dihydro-1H-carbazol-8-yl) acetic acid (Cz4) in aqueous solutions have been studied. The previously unreported TP (Cz4) was isolated by LC and completely characterized by NMR and MS. UV-absorption spectra of diclofenac and three of its TPs were determined and used to calculate disappearance quantum yields. The dominating transformation pathway of diclofenac occurs via initial formation of Cz1 and proceeds to form mainly (Cz4) over 200 min of UV-irradiation. A second minor transformation pathway, which yields Ald as the sole product, was observed only under deaerated conditions.