Reactions of FeIInta and FeIIedda with Hydrogen Peroxide

Article abstract of DOI:10.1021/ja00223a013

Reactions of ferrous nitrilotriacetate (nta) and ethylenediamine-N,N'-diacetate (edda) complexes with hydrogen peroxide at neutral pH in the presence of formate lead to transient intermediates characterized by absorptions near 280 and 400 nm as previously observed for hedta as a ligand.The decomposition of hydrogen peroxide by Fe^IIInta and-edda leads to ligand destruction, which is not inhibited by formate.During this process a reactive intermediate is scavenged by ABTS <2,2'-azinobis(3-ethyl-2,3-dihydrobenzothiazole-6-sulfonate)> at concentrations of the latter that are much higher than expected if the hydroxyl radical were the reactive intermediate.This intermediate is not scavenged by the bromide ion.These stopped-flow and steady-state experiments give evidence for the following reactions (HL = nta, edda): (a) HLFe^II + H2O2 -> HLFe(H2O2), (b) HLFe(H2O2) + HLFe^II + 2H⁺ -> 2HLFe^III + 2H2O, (c) HLFe(H2O2) + HCO2^- -> L^.Fe^II + CO2^.- + 2H2O, (d) HLFe(H2O2) + H⁺ -> L⁺Fe^II + 2H2O, (e) HLFe(H2O2) + ABTS + 2H⁺ -> HLFe^III + ABTS^.+ + 2H2O.Reactions b-e are ascribed to a compound designated as HLFe(H2O2) in reaction a, which might be a hypervalent iron complex HLFe^IV(OH^-)2 but not a hydroxyl radical.The ability of the HLFe(H2O2) complex to oxidize ethanol but not bromide suggests a one-electron reduction potential greater than E^0'(CH3^.CHOH,H⁺/CH3CH2OH) = 1.2 V at pH 7 and smaller than E⁰(Br2^.-/2Br^- = 1.63 V.