Hydroxyl radical reaction with monuron

On the example of monuron, aromatic ring hydroxylation reactions were studied by Density Functional Theory calculations. In order to model the aqueous media the Solvation Model Density technique was used. Based on the relatively low activation energies of hydroxyl radical additions to ipso-, ortho- and meta-positions of the benzene ring (19-42 kJ mol−1 ) and also the Gibbs free energies ((-16)-(-41) kJ mol−1 ) of reactions, hydroxyl radical addition to any of these positions may take place. However, according to the calculations the ortho-addition is preferred in agreement with the experimental results. In these reactions hydroxycyclohexadienyl type radicals form. The first step in the mechanism of para-reaction is OH/Cl substitution without cyclohexadienyl type intermediate. The results of theoretical calculations here are also in agreement with the experimental results which show that the hydroxyl radical reaction with monuron in 40% results in Cl elimination