pH-induced mechanistic changeover from hydroxyl radicals to iron(IV) in the Fenton reaction

TitlepH-induced mechanistic changeover from hydroxyl radicals to iron(IV) in the Fenton reaction
Publication TypeJournal Article
Year of Publication2012
AuthorsBataineh H, Pestovsky O, Bakac A
Journal TitleChemical Science
Volume3
Pages1594-1599
Date Published05
Type of ArticleArticle
ISBN Number2041-6520
Accession NumberWOS:000302319000031
Keywordsaerated water, AQUEOUS-SOLUTION, as(iii) oxidation, atom transfer, ferryl ion, HYDROGEN-PEROXIDE, reagent generation, solvent water, zero-valent iron, zerovalent iron
Abstract

A major pathway in the reaction between Fe(II) and H2O2 at pH 6-7 in non-coordinating buffers exhibits inverse kinetic dependence on [H+] and leads to oxidation of dimethyl sulfoxide (DMSO) to dimethyl sulfone (DMSO2). This step regenerates Fe(II) and makes the oxidation of DMSO catalytic, a finding that strongly supports Fe(IV) as a Fenton intermediate at near-neutral pH. This Fe(IV) is a less efficient oxidant for DMSO at pH 6-7 than is (H2O)(5)FeO2+, generated by ozone oxidation of Fe(H2O)(6)(2+), in acidic solutions. Large concentrations of DMSO are needed to achieve significant turnover numbers at pH >= 6 owing to the rapid competing reaction between Fe(II) and Fe(IV) that leads to irreversible loss of the catalyst. At pH 6 and <= 0.02 mM Fe(II), the ratio of apparent rate constants for the reactions of Fe(IV) with DMSO and with Fe(II) is similar to 10(4). The results at pH 6-7 stand in stark contrast with those reported previously in acidic solutions where the Fenton reaction generates hydroxyl radicals. Under those conditions, DMSO is oxidized stoichiometrically to methylsulfinic acid and ethane. This path still plays a role (1-10%) at pH 6-7.

URL<Go to ISI>://WOS:000302319000031
DOI10.1039/c2sc20099f
Alternate JournalChem. Sci.