THE OXIDATIVE DECHLORINATION REACTION OF 2,4,6-TRICHLOROPHENOL IN DILUTE AQUEOUS SUSPENSIONS OF MANGANESE OXIDES

Oxidation of 2,4,6-trichlorophenol (TCP) by layered manganese oxides (Na and Co-buserite) in dilute acidified aqueous suspension gives 2,6-dichloro-p-benzoquinone as a major product. This compound is likely to further polymerize and become incorporated into humuslike materials. The oxidation rate was higher at lower pH and higher on Na-buserite compared to Co-buserite. TCP reacted at a faster rate than unsubstituted phenol at pH 3 and 5.5, which is explained by (a) the lower half-wave potential of TCP compared to phenol; (b) a stronger bond dipole associated with the electronegative halogen, favoring an addition step in nucleophilic substitution; and (c) easier depronation of TCP at the manganese oxide-water interface due to its lower pK(a). IR spectroscopy shows that TCP adsorbs in deprotonated form on the surface of manganese oxide, and it cannot be washed from the surface by water. Nucleophilic attack by addition-elimination is suggested as a mechanism of TCP dechlorination and oxidation.