An E.S.R. Investigation of the Reactive Intermediate Generated in the Reaction Between FeII and H2O2 in Aqueous Solution. Direct Evidence for the Formation of the Hydroxyl Radical

The technique of E.S.R. spectroscopy, when employed in conjunction with a continuous flow system, provides direct evidence for the nature of free radicals formed from organic substrates in the presence of Fe^II and H₂O₂ in aqueous solution. It is shown, both via the identification of hydroxyl-radical adducts to alkenes and via the observed site-selectivity of radical attack, that the hydroxyl radical is formed as the reactive intermediate in the presence of various chelators (e.g. EDTA, DTPA). This approach also allows the rate constants for the Fe^II-H₂O₂ reaction in the presence of the different chelates to be determined; values obtained are in reasonable agreement with most of those measured by other methods. Examples of radical oxidation (by Fe^III) and reduction (by Fe^II) are revealed.