MECHANISM OF PHOTODEGRADATION OF AQUEOUS ORGANIC POLLUTANTS .2. MEASUREMENT OF THE PRIMARY RATE CONSTANTS FOR REACTION OF OH RADICALS WITH BENZENE AND SOME HALOBENZENES USING AN EPR SPIN-TRAPPING METHOD FOLLOWING THE PHOTOLYSIS OF H2O2

The technique of spin trapping, with EPR detection of spin adducts, has been applied to the study of the photodegradation of benzene, chlorobenzene, bromobenzene, iodobenzene, o-dichlorobenzene, m-dichlorobenzene, and p-dichlorobenzene sensitized by the photolysis of H2O2 in aqueous solution. By employing a competition kinetic scheme and relative initial slopes or signal amplitudes, plus published rate constants for the reaction of OH radicals with the spin trap (DMPO), it has been possible to obtain rate constants for the reaction of OH radicals with benzene and its halo derivatives. Rate constants obtained by this method at neutral and acidic solutions are similar to published methods using pulse radiolysis, where available. Significant differences were found for measurements carried out in basic solutions. The rate constants do not vary much among the halobenzene derivatives studied, and an average rate constant of approximately 5.0 x 10(9) M-1 s-1 could be used for any of these compounds.