Mechanistic pathways of the photolysis of paracetamol in aqueous solution: an example of photo-Fries rearrangement.

The mechanism of the photolysis of N-(4-hydroxyphenyl)ethanamide (paracetamol, PA), a widely prescribed analgesic and antipyretic drug, has been investigated in the absence and in the presence of oxygen. Identification of products and kinetic analyses were performed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) and by ultra-performance liquid chromatography with a diode array detector (UPLC-PDA). The results show that, under irradiation at 254 nm and independently of the presence of oxygen, the predominant reaction pathway is a photo-Fries rearrangement (PFR), yielding the PA isomer 2'-amino-5'-hydroxyacetophenone (PAI).

Degradation of 2,4-dihydroxibenzoic acid by vacuum UV process in aqueous solution: kinetic, identification of intermediates and reaction pathway.

2,4-Dihydroxybenzoic acid (2,4-DHBA) is found frequently as a pollutant in natural waters and represents a threat to water quality because it is a precursor to the formation of quinones which are highly toxic. The degradation of 2,4-DHBA using the vacuum UV photolysis of water has been investigated. Irradiation was carried out in an annular photoreactor equipped with a Xe-excimer lamp situated in the centre and emitting at 172 nm.

Hydrogen peroxide evolution during V-UV photolysis of water.

Hydrogen peroxide evolution during the vacuum-ultraviolet (V-UV, 172 nm) photolysis of water is considerably affected by the presence of oxalic acid (employed as a model water pollutant) and striking differences are observed in the absence and in the presence of dioxygen.