Oxidation of chloroanilines at metal oxide surfaces

The oxidation reaction of chlorinated anilines by two manganese oxides, birnessite and pyrolusite, and by iron oxide has been investigated. The oxidation ability of the oxides was in the order birnessite >> pyrolusite > iron oxide. Birnessite removed 100% of chloroanilines in 30 min, whereas pyrolusite and iron oxide removed from 5 to 96% of chloroanilines in 72 h. The differences in the reactivity of chloroanilines depended on the number and the position of chloro substituents on the aromatic ring. The activity of the oxides was maximal at pH 4.0 and decreased as the pH increased. The reaction kinetics in each of the systems investigated was adequately described by a second-order rate expression. A free-radical mechanism for the oxidative coupling reaction of chlorinated anilines was suggested. Chloroazobenzene and chlorohydroxydiphenylamine dimers were detected among the oxidation products. The results obtained suggested that the oxidative mechanism occurred through a head-to-head and head-to-tail coupling of chloroanilino radicals.