The detection of a complex intermediate in the oxidation of ascorbic acid by ferric ion

Abstract

The oxidation of ascorbic acid by Fe³⁺ ion has been studied using the stopped-flow technique in an attempt to detect and study the formation of an intermediate. It has been shown that a transient species, believed to be a ferric ascorbate complex, and exhibiting a broad absorption band with λ_max.= 560 nm is formed by a two-step mechanism. Values of 11 ± 6 l mol^–1 cm^–1 and 0·55 ± 0·4 for the extinction coefficient and formation constant respectively at 25 °C have been obtained for the overall complex formation. At 0 °C, the first step in the reaction is governed by the law, Rate =k[Fe³⁺][H₂A], where k has the value of 30 ± 10 l mol^–1 s^–1. The probable mechanism of both the complex formation and overall redox reaction are discussed.