|MadSci Network: Chemistry|
Hello Lee, The Fenton reagent is a mixture of Fe(II) and hydrogen peroxide. The Fe(II) reacts with the peroxide to form Fe(III), a hydroxyl radical, and a hydroxide anion. If the hydroxyl radical is not trapped by a species that can react with it, another Fe(II) will react with it to form another Fe(III) and another hydroxide anion. This is eqivalent to what is shown schematically below _inside_ the dashed border. The Haber-Weiss cycle is inclusive of the Fenton reaction but regenerates the Fe(II) by oxidation with a peroxyl radical (or dioxygen radical anion if the peroxyl radical first loses a proton) to give oxygen gas as the byproduct. Whether or not a Fenton reaction becomes a Haber-Weiss cycle depends on the stoichiometries of the reactants. Qualitatively, if there is a lot of hydrogen peroxide and little Fe(II) then the Haber-Weiss cycle is more likely to take place, whereas, if there is very little hydrogen peroxide and lots of Fe(II) then the Fenton reaction alone takes place. The acidity of the reaction mixture is important as well and should be kept well below 7 (therefore acidic). In fact, "available hydroxyl radical" can be calculated based on the pH of the reaction. The advantage of the Fe(III) process is that it _must_ go through the Haber-Weiss cycle and therefore must be catalytic in iron. For any process that requires a heavy metal it is best (for toxicity, waste disposal and cost reasons) if the heavy metal can be present in as little quantity as possible thus making the catalytic method better. I hope this info was helpful Jeremy
Try the links in the MadSci Library for more information on Chemistry.