Oxidation of pentachlorophenol by manganese dioxide

This study examined the oxidative transformation kinetics of pentachlorophenol (PCP) by manganese dioxide (MnO₂) at pH 4.12 solution using manganese dioxide as an oxidant. This study also discussed the influence of pH on the reaction kinetics. Results show that PCP is highly susceptible to oxidation by manganese dioxide. The loss of PCP slows as the reaction progresses and deviates from the simple pseudo-first-order kinetics but follows complex reaction kinetics when experiments were performed at a constant pH and with an enough excess of MnO₂. Furthermore, the reaction rate of PCP decreases significantly as the pH of the reaction mixture increases from 3.5 to 6.6. Using solvent extraction and GC-MS analysis, one minor and two major products were detected. The minor product is the mixture of tetrachloro-1,4-hydroquinone and tetrachlorocatechol, and the two major products are dimeric products that were formed by coupling of pentachlorophenoxy radicals. Furthermore, the two major products are structural isomers, resembling each other except for the position of nine chloride atoms on the aromatic ring. On the basis of the surface reaction kinetics and product identification observed in this study, the reaction scheme for PCP oxidation by manganese dioxide is tentatively proposed.