Interactions of Fe(III) with adrenaline, l-dopa and other catechol derivatives: Electron-exchange kinetics and mechanism in acidic perchlorate media

The electron transfer reaction between Fe(III) and several benzene-1,2-diols (namely, 4-methyl-, 4-t-butyl-, 4-chloro-benzene-1,2-diol, l-Dopa and adrenaline) has been studied with a stopped-flow technique, at 25.0°C, μ = 1.0 M and 0.10 ⩽ [HClO4] ⩽ 0.40 M. The reaction, leading to Fe(II) and the corresponding o-benzoquinone, has been found to follow the kinetic law: Rate = (A + B[Fe(III)][H+]−1)[Fe(III)][Diol][H+]−. Both A and B are strongly influenced by the susceptibility of the substrate to oxidation. Each pathway is discussed with reference to the reacting species, and linear relations between log k and the standard redox potentials of the rate determining step and between ΔG≡ and ΔG° have been found and are discussed.