Abstract:
The degradation of monuron (3-(4-chlorophenyl)-1,1-dimethylurea) and isoproturon (3-4-isopropylphenyl)-1,1-dimethylurea) photoinduced by nitrate and nitrite ions in aqueous solution has been investigated.
The photolysis of monuron at 310 nm gives only one photo-product of hydrolysis. The photolysis of the isoproturon leads several intermediates: oxidations of the N-terminous and isopropyl groups, deisopropylation and the substitution of isopropyl by OH,
elimination of dimethylamine group. It appears that the nature of the substituent on the ring play a major role in the orientation of the reaction.
The transformation photo-inducted of monuron and isoproturon (were investigated in an aqueous solution containing nitrates and nitrites at 310 nm and 365 nm, respectively. In both NO3
− and NO2
− conditions, the degradation of monuron and isoproturon followed
pseudo-first order kinetics. The intermediate products were identified by GC-MS, and the nitration, hydroxylation and coupling reactions were determined. In addition, the oxidation of the N-terminus group, the substitution of chlorine by ˙OH and the nitration by ˙NO2 radical onto the phenyl ring were observed. The photoinduced transformation of monuron was studied under variable conditions of pH, inducer concentration, substrate concentration, humic acids, oxygen content and salts used as hydroxyl radical
scavengers. The photodegradation rates were strongly influenced by all the above parameters.
The degradation of monuron and isoproturon is efficacy in the dark and in the presence of NO2
− as well as in an aqueous solution with the addition of hydrogen peroxide in an acidic medium.
