Reaction of ferrate (VI)/ferrate (V) with hydrogen peroxide and superoxide anion--a stopped-flow and premix pulse radiolysis study.
The reduction of ferrate(VI) to ferrate(V) by superoxide ions was studied over the pH range 2.6-13.0 using the premix pulse radiolysis technique. The pH dependence indicates that only the unstable protonated forms of ferrate, H2FeO4 (pKa3.5) and HFeO4- (pKa7.3) are reactive, k(HFeO4(-) + O2) = (1.7 +/- 0.2) x 10(7) M-1 s-1. The stable ferrate ion, FeO4(2-), showed no significant reactivity towards either hydrogen peroxide or superoxide anion. The rate constants for the spontaneous dimerization and decomposition of the protonated ferrates, e.g. k(HFeO4(-) + HFe04) approximately 250 M-1s-1, are orders of magnitude slower than their corresponding reduction reduction by superoxide indicating an outer-sphere mode of electron transfer for the latter process. In contrast the ferrate(VI) species H3FeO4+ (pKa = 1.6 +/- 0.2), H2FeO4, and HFeO4- oxidize hydrogen peroxide, e.g. k(HFeO4(-) + H2O2) = 170 M-1 s-1), at rates which correspond closely to their dimerization rates suggesting an inner-sphere controlled mechanism.
Rush
J D
JD
Chemistry Department, Brookhavan National Laboratory, Upton, NY 11793-5000, USA.
Zhao
Z
Z
Bielski
B H
BH
D006861:Hydrogen Peroxide; D007202:Indicators and Reagents; D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D016877:Oxidants / Q000737:chemistry*; D017680:Potassium Compounds / Q000737:chemistry*; D011675:Pulse Radiolysis / Q000379:methods; D012996:Solutions; D013481:Superoxides; D013997:Time Factors
D007202:Indicators and Reagents; D058085:Iron Compounds; D016877:Oxidants; D017680:Potassium Compounds; D012996:Solutions; D013481:Superoxides; C044384:potassium ferrate; D006861:Hydrogen Peroxide