Investigation of the photochemistry of urea herbicides (chlorotoluron and isoproturon) and quantum yields using polychromatic irradiation

This paper presents the investigation of the photochemical reaction of chlorotoluron (3-(3-chloro-4-methyl-phenyl)-1,1-dimethylurea) in CH₃CN, hexane, and aqueous and buffered solutions (pH = 4, 7, and 9) and of isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) in aqueous and buffered solutions using a polychromatic light source at a temperature of 22°C. For chlorotoluron, isosbestic points were found (with the exception of hexane as solvent) and ultraviolet spectroscopy was used to obtain kinetic data. The main photoproduct for the photolysis of chlorotoluron in aqueous solutions was identified as 3-(3-hydroxy-4-methyl-phenyl)-1,1 dimethylurea. Quantum yields found in aqueous and buffered solutions were comparable (about 0.07) and 2 times lower and 10 times higher in CH₃CN and hexane, respectively. No isosbestic points were found for isoproturon, and quantum yields of about 0.004 were calculated in all solutions. Chlorotoluron and isoproturon present very low molar extinction coefficients above 290 nm, and they can be assumed to be photostable with respect to direct irradiation by sunlight.