OXIDIZING INTERMEDIATES GENERATED IN THE FENTON REAGENT - KINETIC ARGUMENTS AGAINST THE INTERMEDIACY OF THE HYDROXYL RADICAL

It has long been recognized that the aqueous mixture of hydrogen perox ide and ferrous ion, known as the Fenton reagent, generates powerful o xidants. Furthermore, the chemical intermediates and reaction pathways of the type generated by this reagent have been implicated in oxidati ve damage in biological systems. Although the subject continues to be debated, the hydroxyl radical (OH) is generally invoked as the predomi nant oxidizing intermediate formed by the Fenton reagent. However, rec ent results from this laboratory have demonstrated that the principal pathway for the Fenton-media ted oxidation of N-nitrosodimethylamine d oes not involve OH, but instead must invoke the intermediacy of anothe r strongly oxidizing species. This conclusion was based on stopped-flo w spectrophotometric observation of a transient, A, believed to be an iron(II) nitrosyl adduct, which was formed at a rate fivefold faster t han that predicted for formation of OH. Subsequent experiments have sh own that methanol and other organic compounds can quench the formation of A. This quenching procedure provides a unique spectrophotometric p robe with which to examine the relative reactivities of putative Fento n-type oxidizing intermediates toward organic substrates. Presented he re are the results of several such quenching studies, plus an overview of our mechanistic investigations of the Fenton reaction.