Oxidation of Ferrous Ions by an Aliphatic Dioxyl Radical

Abstract

1-Hydroxy-1-methylethyl radicals react with oxygen with a rate constant of 4.5 ± 0.5 × 109 dm3 mol–1 s–1. The resulting dioxyl radicals react with ferrous ions with a rate constant at 25°C of 1.7 ± 0.2 × 106 dm3 mol–1 s–1, entropy of activation + 99 J °C–1 mol–1. Pulse radiolysis data are consistent with the product of the reaction being a complex, Fe3+RO–2, which is in equilibrium with a bridge compound, Fe3+RO–2Fe2+. The complex disappears in a first order manner with a rate constant at 25°C of 3.85 ± 0.15 × 103 s–1, entropy of activation –82 J °C–1 mol–1. The bridge compound disappears in a first order manner with a rate constant at 25°C of 2.1 ± 0.1 × 104 s–1, entropy of activation –0.9 J °C–1 mol–1. The 1-hydroxy-1-methylethyldioxyl radical has a weak absorption with a peak at 250 nm. Fe3+RO–2 has a weak absorption extending through the visible region of the spectrum. Fe3+RO–2Fe2+ has a stronger absorption with a broad peak at 320 nm. 1-Hydroxy-1-methylethyl radicals react with ferric ions with a rate constant of 4.5 ± 0.5 × 108 dm3 mol–1 s–1.