Oxidative transformation of tetrachlorophenols and trichlorophenols by manganese dioxide.

This study examined the transformation kinetics of three tetrachlorophenols (TeCPs) and three trichlorophenols (TCPs) in the presence of MnO2 under different solution chemistry conditions. The reaction rate measured for each CP decreased as a function of solution pH, and under the same solution chemistry conditions, the measured rates may depend primarily on both the adsorbability at the MnO2 surfaces and the isomeric structures of the CPs. Isomeric effects indicated that chloro substituent on ortho or para positions exhibited faster rates of transformation than on meta positions. Gas chromatography-mass spectrometry analysis with a derivatization method showed that dimers including polychlorinated phenoxyphenols and chlorinated polyhydroxybiphenyl were among the major products for all CPs. Monomeric products were among the major products of 2,4,6-TCP, 2,3,4-TCP, and 2,3,4,6-TeCP, whereas trimeric products also were among the major products of 2,3,4-TCP and 2,4,5-TCP. It appeared that hydroxylation of CPs and formation of dimeric or trimeric products via oxidative coupling were the major reaction mechanisms involved in the oxidation of CPs by MnO2.