Browsing by Author "Jayson, G. G."

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Appearance of Sulphatoferric Complexes in the Oxidation of Ferrous Sulphate Solutions: A Study by Pulse Radiolysis
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (6), 1973) Jayson, G. G.; Parsons, B. J.; Swallow, A. J.
The rate of the reaction between perhydroxyl radicals and ferrous ions, like that between hydroxyl radicals and ferrous ions, is little affected when the ferrous ions are associated with sulphate. However, sulphate ions displace HO–2 from the ferric hydroperoxide complex by an outer-sphere ion-pair formation mechanism (Id): SO2–4+ Fe3+(H2O)6,HO–2⇌ Fe3+(H2O)6,HO–2SO2–4, Fe3+(H2O)6,HO–2SO2–4→ Fe3+(H2O)5SO2–4+ HO–2+ H2O. The equilibrium constant for the first of these reactions is 90 ± 20 M–1, and the rate constant for the second is approximately 104 s–1. Sulphate reacts with the ferric-hydroperoxide-ferrous bridge compound similarly, with an equilibrium constant of 100 ± 20 M–1 and a rate constant of the same order of magnitude as for the ferric hydroperoxide complex. Additional reactions take place when the concentration of sulphate ions is high enough. New determinations have been made of the rate constants and activation parameters for the reaction of hydrated ferric ions with sulphate. A detailed mechanism is given for reactions occurring during irradiation of the Fricke dosimeter in the absence of sodium chloride.
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.
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.