Phototransformation of 3,5-dihalogeno-4-hydroxybenzonitriles (ioxynil and chloroxynil) in aqueous solution

The main initial photochemical reaction of ioxynil and chloroxynil in pure water is the photohydrolysis of C–halogen bond, leading, in both cases, to a monohalogenated dihydroxybenzonitrile. Reduction is observed as a minor pathway, especially when irradiation is carried out in the presence of humic acids. In a second stage, similar reactions occur with the remaining C–halogen bond. The photochemical reactivity is not significantly affected by the nature of the halogen Cl, Br or I.