Photocatalytic degradation of paracetamol: Intermediates and total reaction mechanism

[Display omitted] ► The advanced oxidation of paracetamol with TiO2/UV was investigated. ► HPLC indicated the formation of hydroquinone, benzoquinone, p-aminophenol and p-nitrophenol. ► IR studies indicated that p-nitrophenol and p-aminophenol are also produced. ► PAM photocatalytic reaction mechanism includes an alternative deacylation pathway. The advanced oxidation of paracetamol (PAM) promoted by TiO2/UV system in aqueous medium was investigated. Monitoring this reaction by HPLC and TOC, it was demonstrated that while oxidation of paracetamol is quite efficient under these conditions, its mineralization is not complete. HPLC indicated the formation of hydroquinone, benzoquinone, p-aminophenol and p-nitrophenol in the reaction mixtures. Further evidence of p-nitrophenol formation was obtained following the reaction by UV–vis spectroscopy. Continuous monitoring by IR spectroscopy demonstrated the breaking of the aromatic amide present in PAM and subsequent formation of several aromatic intermediate compounds such as p-aminophenol and p-nitrophenol. These aromatic compounds were eventually converted into trans-unsaturated carboxylic acids. Based on these experimental results, an alternative deacylation mechanism for the photocatalytic oxidation of paracetamol is proposed. Our studies also demonstrated IR spectroscopy to be a useful technique to investigate oxidative mechanisms of pharmaceutical compounds.