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 >> pyr
olusite > iron oxide. Birnessite removed 100% of chloroanilines in 30
min, whereas pyrolusite and iron oxide removed from 5 to 96% of chloro
anilines 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 de
creased as the pH increased. The reaction kinetics in each of the syst
ems investigated was adequately described by a second-order rate expre
ssion. A free-radical mechanism for the oxidative coupling reaction of
chlorinated anilines was suggested. Chloroazobenzene and chlorohydrox
ydiphenylamine dimers were detected among the oxidation products. The
results obtained suggested that the oxidative mechanism occurred throu
gh a head-to-head and head-to-tail coupling of chloroanilino radicals.