Kinetics of oxidation of chlorobenzenes and phenyl-ureas by Fe(II)/H2O2 and Fe(III)/H2O2. Evidence of reduction and oxidation reactions of intermediates by Fe(II) or Fe(III)

The rates of degradation of 1,2,4-trichlorobenzene (TCB), 2,5-dichloronitro benzene (DCNB), diuron and isoproturon by Fe(II)/H2O2 and Fe(III)/H2O2 have been investigated in dilute aqueous solution ([Organic compound], 2 1 muM, at 25.0 +/- 0.2 degreesC and pH less than or equal to 3). Using the relati ve rate method with atrazine as the reference compound, and the Fe(II)/H2O2 (with an excess of Fe(II)) and Fe(III)/H2O2 systems as sources of OH radic als, the rate constants for the reaction of OH. with TCB and DCNB were dete rmined as (6.0 +/- 0.3)10(9) and (1.1 +/- 0.2)10(9) M-1 s(-1). Relative rat es of degradation of diuron and isoproturon by Fe(II)/H2O2 were about two t imes smaller in the absence of dissolved oxygen than in the presence of oxy gen. These data indicate that radical intermediates are reduced back to the parent compound by Fe(II) in the absence of oxygen. Oxidation experiments with Fe(III)/H2O2 showed that the rate of decomposition of atrazine markedl y increased in the presence of TCB and this increase has been attributed to a regeneration of Fe(II) by oxidation reactions of intermediates (radical species and dihydroxybenzenes) by Fe(III). (C) 2000 Elsevier Science Ltd. A ll rights reserved.