Strong Inhibition of the Fe3+ + H2O2 Reaction by Ethanol: Evidence against the Free Radical Theory

The effect of ethanol on the catalytic decomposition of H2O2 by Fe3+ was investigated. While expecting a simple competitive oxidation of C2H5OH, far more complex kinetics were encountered experimentally: already minute amounts of C2H5OH (1% of H2O2) had a powerful retardation effect on the disappearance of H2O2. This fact indicated the operation of an intricate mechanism. It excluded the possibility of OH• radicals being the active agents in the oxidation: OH• radicals generated by radiolysis react with C2H5OH with a very high rate constant. The interpretation of the experimental results was based on a mechanism involving iron in a +5 oxidation state (FeO3+) as the active intermediate and its binding in complex structures in which activity is reduced. The question of free radical versus non-radical mechanisms is discussed. The conclusions differ from generally accepted concepts in relation to the Fenton and related reactions.