Light-induced transformation of alkylurea derivatives in aqueous TiO2 dispersion

The light-induced degradation of alkyl-urea derivatives under simulated solar irradiation has been investigated in aqueous solutions containing TiO2 as a photocatalyst. Herein, we will focus on how the presence of one or more methyl (or ethyl) groups on urea modifies the kinetics of disappearance and influences both the ratio and the extent of the inorganic nitrogen formation, due to the existence of different degradation pathways. In the present work, we have elucidated a mechanism of formation of transformation products of the alkyl derivatives by combining several analytical and spectroscopic procedures and the theoretical simulation of ab initio calculation. In all cases, N-demethylation represents only a secondary pathway, while the main transformation proceeds via an unexpected cyclization, involving (m)ethyl- and di(m)ethyl-ureas with the formation of (methyl)-amino-2,3-dihydro-1,2,4-oxadiazol-3-one as the principal intermediate of the reaction (yield of 60%). This behaviour is rather surprising and in contrast with the typical photocatalysed transformation pathways, that proceed through the formation of more simple structures.