Main pathways in the photochemical transformation of 3-(4-bromophenyl)-1-methoxy-1-methylurea (metobromuron) in aqueous solution

Metobromuron (MB) in aqueous solution has a complex photochemical behaviour due to the involvement of two main different routes: demethoxylation of ur ea moiety and reactions (hydroxylation, oxidation, formation of adducts) re sulting from the initial formation of a carbene. Both pathways occur in app roximately equal proportions in the case of MB. Comparison with other halog enophenylureas indicates that the position of the halogen atom on the ring and the nature of the substituent on the urea moiety play an important role in the relative importance of these two pathways: the carbene pathway is r elated to the presence of a halogen atom in para-position on the ring and N -demethoxylation is much easier than N-demethylation. Hydroxylation of the ring without debromination. was also observed. The photocatalytic degradati on also leads to the formation of several products resulting from hydroxyla tion of the ring and demethoxylation. (C) 2001 Elsevier Science B.V. All ri ghts reserved.