Mannitol is a well-known radical trapping reagent, though the trapping effect is difficult to confirm in a Fenton reaction. Under acidic conditions, mannitol was consumed during the Fenton reaction, as well as other substrates, such as vanillyl alcohol, veratryl alcohol and Methyl-β-D-glucopyranoside. Under alkaline conditions, however, only mannitol was consumed during the reaction.
When we investigated the solubility of iron (II) and (III), which work as catalysts to initiate the Fenton reaction, the addition of mannitol was found to help dissolve the iron compounds in alkaline solution, especially those exceeding pH 10, though iron compounds are not soluble under such alkaline conditions. Based on this result, mannitol is considered to form a complex with iron (II) and (III) ions under these conditions and the hydroxyl radical (HO•) generated by the reaction between hydrogen peroxide and iron (II) and (III) complex of mannitol will attack the mannitol because it is the compound nearest the site where the HO• is generated.