Abstract:
Experimental and theoretical studies of electronic spectra of paracetamol in water after exposure to UV radiation are presented. Theoretical studies were performed using the quantum-chemical modified INDO/s method. Paracetamol-water complexes in a 1:1 ratio were determined. Chemical bonds of paracetamol were revealed, the rupture of which leads to the formation of several photoproducts. To interpret changes in the absorption spectra of paracetamol after exposure to UV radiation, electronic absorption spectra of the identified photoproducts and their complexes with the paracetamol anion were calculated. It was shown that the rupture of chemical bonds and the formation of paracetamol photoproducts occurs in the singlet state by the predissociation mechanism. The calculation results are confirmed by experimental data. Three photoproducts (2-amino-5-hydroxyacetophenone, para-aminophenol, peroxyether) formed as a result of the rupture of single bonds in the CHCOCH$_3$ fragment were proven. It has been shown that the band in the absorption spectrum in the region of $\lambda_{\mathrm{max}}$ = 380 nm after UV irradiation of paracetamol in water is formed by a structure composed of hydrogen-bonded complex at the oxygen of the carboxyl group of the paracetamol anion with the main photoproduct of its decay –
2-amino-5-hydroxyacetophenone.
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