James D. Rush

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.

Pulse radiolysis studies of alkaline iron(III) and iron(VI) solutions. Observation of transient iron complexes with intermediate oxidation states.

The first spectroscopic evidence for complexes containing iron formally in the IV and V oxidation states in the presence of a simple ligand, i.e., OH/sup -/ and P/sub 2/O/sub 7//sup 4 -/ in alkaline solution is reported. These transient species are obtained by pulse radiolysis of alkaline ferric (Fe(III)) and ferrate (Fe(VI)) solutions by using the hydroxyl radical or its conjugate base, O/sup -/, and the aquated electron, e/sub aq//sup -/, as the respective oxidizing and reducing agents. 18 references, 1 figure.

Complexes of silver(III) with oxoanions

Abstract Silver(III) has a half-life at pH 11 of several hundred seconds in aqueous solutions in the presence of 0.1–1.0 M concentrations of certain basic oxoanions (Oxo) (phosphate, carbonate, borate, pyrophosphate, and arsenate). This compares with a lifetime of a few seconds at pH 11 in the absence of these oxoanions. UV-visible spectra and kinetic data for these solutions are interpreted as evidence for the following equilibria in the pH range 9–13. Ag(OH) 4 −1 + H 2 O ⇌ Ag(OH) 3 H 2 O + OH − (1) Ag(OH) 4 −1 + Oxo ⇌ Ag(OH) 3 Oxo + OH − (2) Ag(OH) 3 Oxo + H 2 O ⇌ Ag(OH) 2 (Oxo)H 2 O + OH − (3) Values of K 3 lie in the range 10 −3 K 3 4 M for the systems studied. K 2 is estimated to be ∼10 2 for phosphate and slightly smaller for the other systems. Ag(OH) 4 − undergoes an unusual reaction with pyrophosphate at pH ∼ 8 to form a novel silver(II) complex, [Ag(P 2 O 7 ) 2 ] 6− , for which EPR and electronic absorption spectral parameters are reported.