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Subject: search.filters.subject.Ferrous Ions

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    Oxidation of Ferrous Ions by Perhydroxyl Radicals
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (1), 1973) Jayson, G. G.; Parsons, B. J.
    The rate of the reaction between HO2 radicals and Fe2+ is dependent on temperature, the rate constant at 20 C being 9.1 +0.4x 105 M-1 s-1 (1.2±0.05x 106 M-1 s-1 at 25^C) and the activation energy 10.0± 1.0 kcal mol-1 (42 kJ mol-1). The initial reaction product is considered to be an outer-sphere complex between Fe31 and HO2. This hydroperoxide complex appears to react with Fe2+ in a fast reversible reaction to give a bridge compound. The absorption spectra of the two complexes have been measured. The molar extinction coefficients at 450 nm arc 140± 50 M-1 cm-1 and 1240+100 M-1 cm-1, respectively. The equilibrium constant for the formation of the bridge compound varies from 22 + 2 M-1 at 20°C to 37.5 ±0.5 M-1 at 40°C. The hydroperoxide complex dissociates unimolecularly with a rate constant at 20 or 25°C of 1.8 ±0.1 x 103 s-1, activation energy 2.1 ±0.2 kcal mol-1. The bridge compound dissociates unimolecularly with a rate constant at 20°C of 1.8±0.1 x 104 s-1 (2.5±0.1 x 104 s-1 at 25°C), activation energy 11.4± 1.1 kcal mol-1. The final product of the whole reaction is the hydrated ferric ion.
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    Oxidation of Ferrous Ions by Hydroxyl Radicals
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (11), 1972) Jayson, G. G.; Parsons, B. J.; Swallow, A. J.
    Hydroxyl radicals have been found by pulse radiolysis to oxidize hydrated ferrous to ferric ions with a rate constant of (2.3 ± 0.2)× 108 M–1 s–1. The corresponding reaction of OD radicals in D2O solution has a rate constant of (9.4 ± 0.8)× 107 M–1 s–1. OD radicals oxidize ferrocyanide in D2O solution with (9.7 ± 1.0)× 109 M–1 s–1. The mechanism of the oxidation of ferrous ions is though to consist of simple electron transfer, and the difference in rate between H2O and D2O solution is attributed to differences between free energies of hydration in the two solvents.