New Insights of the Fenton Reaction Using Glycerol as the Experimental Model. Effect of O₂, Inhibition by Mg²⁺, and Oxidation State of Fe

Abstract

The use of iron ions as catalyst of oxidation with hydrogen peroxide, known as the Fenton reaction, is important for industry and biological systems. It has been widely studied since its discovery in the 19th century, but important aspects of the reaction as which is the oxidant, the role of oxygen, and the oxidation state of Fe still remain unclear. In this work new mechanistic insights of the oxidation of carbohydrates by the Fenton reaction using glycerol as experimental model are described. The reaction was studied by means of oxidation reduction potential (ORP) measures. The stoichiometry was measured, showing the important role of oxygen for lowering H2O2 consumption under aerobic conditions. Evidence is provided to demonstrate that in this system Fe(2+) generates a catalyst by reacting with a substrate to produce a complex, which gives rise to singlet oxygen after reacting with H2O2. This is the first time that the inhibitor effect of Mg(2+) is reported in this reaction, and its participation in the mechanism is described. A rational mechanism for the oxidation of glycerol using the Fenton reaction under these specific conditions is proposed. The role of oxygen, the participation of Fe(2+), and the inhibition by Mg(2+) are fully demonstrated experimentally.

Overcoming Catalyst Residue Inhibition of the Functionalization of Single-Walled Carbon Nanotubes via the Billups–Birch Reduction

“…If the iron catalyst residue catalyzes the quenching, then the Fenton oxidation could be a comparable reaction, whereby Fe­(II) and Fe­(III) undergo electron transfer. The kinetics of the Fenton reaction have been extensively studied and the activation energy is ordinarily in the range of 2–50 kJ mol –1 . − Our determined value is clearly within this rather broad range, suggesting that it is consistent with (although not unique to) a comparable electron transfer reaction.…”

QSAR studies of the antioxidant activity of anthocyanins

“…Anthocyanins are known to remove H 2 O 2 from cells that mainly occurs by the Fenton reaction. It takes place through the hydroxyalkene group of of the anthocyanin structures via the mechanism proposed for this reaction (Vitale et al 2016). Hence, a large part of their bioactivities can be explained by this important function.…”

Fates of Organic Hydroperoxides in Atmospheric Condensed Phases

“…Even reactive α-HHs can survive more than a day under certain conditions (e.g., neutral pH, low water content, low temperature). − In that case, transition metals in the condensed phase will be a species that can react with peroxides. The key issue is that the mechanisms of the Fenton (Fe 2+ + H 2 O 2 ) and Fenton-like reactions (Fe 2+ + ROOH/ROOR′) are still not fully understood. − Recent experiments have revealed that the formation of reactive intermediate species depends on the pH, coreactants, and water content of the reaction medium. ,− For example, in a water-poor medium, the reaction of Fe 2+ with H 2 O 2 produces oxo–ferryl (Fe IV O 2+ ) species and other products rather than OH radicals. ,,− It has been reported that in a dry acetonitrile solution, the Fenton reaction exclusively produces Fe IV O 2+ , while the reaction in the presence of >10% water in the solution produces OH-radicals . Furthermore, the decomposition of methyl hydroperoxide CH 3 OOH and ethyl hydroperoxide C 2 H 5 OOH in the presence of Fe 2+ in water at pH 2 produces corresponding alkoxy radicals RO • , rather than OH-radicals .…”