Transformation of fenuron induced by photochemical excitation of humic acids

When neutral solutions containing the herbicide 3-phenyl-1,1-dimethylurea (fenuron) and a humic acid are irradiated at 365 nm, 3-(4-hydroxyphenyl)-1,1-dimethylurea and three biphenyl products are formed as main products. The apparent quantum yield of fenuron disappearance is evaluated as 6·2 × 10−5 mole E−1. Upon irradiation of the same mixture at 253·7 nm, both direct and induced phototransformations of fenuron occur. Direct photooxidation yields 2- and 4-amino-N,N-dimethylbenzamide. The induced phototransformation leads to 2- and 4-hydroxylation of the aromatic ring in accordance with the fact that hydroxyl radicals are involved in the oxidation.