Mechanism and stoichiometry of the redox reaction between iron(III) and caffeic acid

The stoichiometry of the redox reaction of caffeic acid with iron(III) was determined at pH 2.5. A linear increase in the yield of iron(II) was found with increasing iron(III) concentration until reached constant values when iron(III)/caffeic acid molar ratios were higher than 9. The reaction proceeds through two steps each having different rates, and involving intermediates with different redox activities. A mechanism of the redox reaction consistent with our results is proposed.