The oxidation of 6-hydroxydopamine in aqueous solution. Part 3. Kinetics and mechanism of the oxidation with iron(III)

Abstract

The kinetics of the oxidation of 6-hydroxydopamine [5-(2-aminoethyl)benzene-1,2,4-triol, protonated form H3LH+] by iron(III) under anaerobic conditions are presented. A complex mechanism whereby the o- (oQ), p- (pQ), and triketo-quinones (tQ) are formed via parallel inner- and outer-sphere electron transfer mechanisms has been established. The outer-sphere mechanism is particularly fast (nearly diffusion limiting) and predominates. By following the dependence of the rate on ionic strength it has been shown that a deprotonated form of 6-hydroxydopamine reacts via an outer-sphere reaction with all species of iron. Like the other catecholamines [3,4-dihydroxy-1-(2-aminoethyl)benzenes], but to a..