Indirect Fenton reaction

A fundamental aspect of irradiated, aqueous systems is indirect action over a range of concentrations of solute. Fenton reagent provides free radicals, and it might be expected that, within certain limits, yields of products would be independent of the concentration of carbohydrate. However, for a fixed amount of iron (II) sulfate and hydrogen peroxide, yields of carbon dioxide from D-glucono-1,4-lactone indicate otherwise. In part, this result must be attributed to competition of radicals, and it is to be expected that, as the initial n-glucono-l, 4-lactone] [Fe 3 ratio is increased, reactions (19), (22), and (23) will become less important. 

The evidence for the free radical mechanisms of the reaction between ferrous and ferric ions and hydrogen peroxide is fully discussed in the article by J. H. Baxendale in this volume, and it is necessary here only to summarize and comment on those features especially relevant to hemoprotein reactions. This evidence is essentially indirect. Experiment shows very reactive intermediates to be present and extensive kinetic studies reveal competition reactions for these intermediates in that the overall order of the reaction is found to depend on the reactant concentrations. A free radical mechanism is adopted because it accounts for the chemical reactivity of the system in the oxidation of substrates (Fenton s reaction) and the initiation of the polymerization of vinyl compounds (Baxendale, Evans, and Park, 84) and it provides a set of reactions which largely account for the observed kinetics. The set of reactions which fit best the most recent experimental data is that proposed by Barb, Baxendale, George, and Hargrave (83) ... 

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