CONVERSION OF PENTAHALOGENATED PHENOLS BY MICROPEROXIDASE-8 H2O2 TO BENZOQUINONE-TYPE PRODUCTS/

This study reports the microperoxidase-8 (MP8)/H2O2-catalyzed dehaloge nation of pentafluorophenol and pentachlorophenol, compounds whose tox ic effects and persistence in the environment are well documented. The primary products of this dehalogenation reaction appear to be the cor responding tetrahalo-p-benzoquinones. Under the conditions used, the f luorinated phenol and its intermediate products are more susceptible t o degradation than the corresponding chlorinated analogue and its prod ucts. The main degradation products of tetrachloro-p-benzoquinone and tetrafluoro-p-benzoquinone were identified as trichlorohydroxy-p-benzo quinone and trifluorohydroxy-p-benzoquinone, respectively. This second ary conversion of tetrafluoro-p-benzoquinone and tetrachloro-p-benzoqu inone was not mediated by MP8, but was driven by H2O2. Evidence is pre sented for a mechanism where H2O2 molecules and not hydroxide anions a re the reactive nucleophilic species attacking the tetrahalo-p-benzoqu inones. In addition to the formation of the trihalohydroxy-p-benzoquin ones, the formation of adducts of the tetrahalo-p-benzoquinone product s with ethanol, present in the incubation medium, was observed. The ad duct from the reaction of tetrachloro-p-benzoquinone with ethanol was isolated and identified as trichloroethoxyquinone. Thus, the present p aper describes a system in which the formation of tetrahalo-p-benzoqui none-type products by an oxidative heme-based catalyst could be unequi vocally demonstrated.