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.