THE FENTON REAGENTS

Numerous transition metal ions and their complexes in their lower oxid ation states (L(m)M(n+)) were found to have the oxidative features of the Fenton reagent, and, therefore, the mixtures of these metal compou nds with H2O2 were named ''Fenton-like'' reagents. Using the Marcus th eory and the experimental data in the literature, it is shown that in most cases the reaction of these metal complexes with H2O2 is unlikely to occur via an outer-sphere electron-transfer mechanism. It is sugge sted that the first step in this process is the formation of a transie nt complex L(m)M-H2O2n+, which may decompose to an .OH radical or a hi gher oxidation state of the metal, L(m)M(n+2)+, or it may yield an org anic free radical in the presence of organic substrates. Thus, the que stion whether free 'OH radicals are being formed or not via the Fenton reaction depends on the relative rates of the decomposition reactions of the metal-peroxide complex and that of its reaction with organic s ubstrates. Contradictory conclusions described from the study of diffe rent systems might only indicate that these relative rates are differe nt in these systems.