Fenton’s reaction was first discovered by H.J.H Fenton when he first observed the oxidative properties in various metals which could further improve the usage of already discarded, unstable, and poisonous hydrogen peroxide. This discovery in the chemical field not only explored the benefits of hydrogen peroxide but also attracted attention to the strong catalytic power of some metals which could generate highly reactive hydroxyl radicals. Presently iron-catalyzed hydrogen peroxide reactions are called Fenton's reactions and they have many applications in various chemical industries.
Before discussing the mechanism of Fenton's reaction it is important to discuss the commonly used Fenton's reagent. It is a solution of hydrogen peroxide $\mathrm{(H_2O_2)}$ and any ferrous ion preferably iron(II) sulfate or $\mathrm{FeSO_4}$. Its formula is $\mathrm{FeH_4O_6S_2^+}$. Its major usage in the present scenario is in wastewater management where due to its strong catalytic property it is used in the oxidation of contaminants.
The mechanism of Fenton's reaction can be broken down into certain steps in a sequential manner as explained below.
The beginning of the Fenton's reaction is by the oxidation process where ferrous ions $\mathrm{Fe^{2+}}$ are oxidized to ferric ions $\mathrm{Fe^{3+}}$ in the presence of hydrogen peroxide as an oxidizing agent. This first step leads to the production of a hydroxide ions and hydroxyl free radicals as byproducts.
The next step in Fenton's reaction is the opposite of the above-mentioned first step. Here reduction happens where the ferric ion formed is reduced to a ferrous ion in the presence of another hydrogen peroxide molecule. This leads to the regeneration of ferrous ion catalysts and the production of proton and hydroperoxy free radicals as by-products.
Here two different kinds of oxygen radicals are formed because of the disproportionation of hydrogen peroxide in Fenton's reaction. The hydroxide ions and the protons are formed previously as by-products and also combine to generate water molecules in the disproportionation reaction.
After the formation of hydroxyl radicals as mentioned above, it starts its reaction with various compounds present in the vicinity which act as pollutants or hazardous materials. It can undergo addition, hydrogen abstraction, electron transfer, and radical interactions with the pollutants.
Figure 1: Mechanism of Fenton Reaction
Fenton reagent or Fenton reaction as a whole process has many applications and usages in the chemical industry and academic laboratories especially in organic synthetic methodologies as a catalyst. Let us discuss various examples where it has been used.
Fenton’s reaction is used in the conversion reaction of benzene to phenol.
Transformation of barbituric acid to alloxan is possible due to the catalytic activity of Fenton's reagent.
The Haber-Weiss reaction which produces hydroxyl radical and hydrogen peroxide and superoxide is based on the first step of Fenton's reaction mechanism.
Another major organic synthesis where Fenton's reaction a contribution is the coupling reaction of alkanes.
Fenton’s reaction has a crucial role in curbing radioactive contamination, soil pollution, sludge formation, and in wastewater management.
From an ecological perspective, it can be used for biodegradability improvement and as a potential BOD (Biological Oxygen Demand) remover.
It also deals with chemical waste and toxicity by destructing organic pollutants.
Fenton’s reaction can come in handy in odor elimination and color removal.
Fenton’s reaction was first reported and discovered by H.J. Fenton and it discusses the hidden potential of hydrogen peroxide as an oxidizing agent when Fe compounds are used as catalysts in highly acidic conditions.
With the passage of time and enhanced scientific information development, Fenton like reactions were implemented with other metals with low oxidation states and were used as hazardous organic material destructors.
Q1. What is the effect of environmental pH on Fenton’s reaction?
Ans. Ferric ions used in Fenton's reaction are very selective in terms of their solubility and act as a limiting factor in the reaction rate of Fenton's reaction. So the pH of the environment impacts the overall dynamic of Fenton's reaction. Under acidic conditions, the reaction rate is fast due to the easy solubility of ferric ions in the acidic medium. On the contrary, under alkaline conditions, the reaction slows down due to the precipitation of ferric ions.
Q2. Give a brief about the electro-Fenton process.
Ans. The electro-Fenton process is similar to the conventional Fenton's reaction but is advanced in its approach as an electrochemical oxidation process where hydroxyl radicals are generated in situ using electrocatalytic ways. This process has shown high efficiency instead of the usual method.
Q3. How does Fenton's reaction happen in the human body?
Ans. The connecting link between Fenton's reaction and the human body is iron. Iron is one of the most important and abundant minerals in the human body and has properties that are significant for living longevity and sustainability. On the other hand, Fenton's reaction is between iron and hydrogen peroxide which generates strong hydroxyl radicals. The generation of these strong oxidative hydroxyl radicals is toxic to the human body and affects it badly at the cellular level.
Q4. Name the reactive oxygen species produced in Fenton’s reaction.
Ans. The major reactive oxygen species formed during Fenton's reaction is the high valent oxoiron(IV) species. The species is formed due to the reaction of Fe(II) and H2O2 in an aqueous medium.
Physics
Biology
Chemistry
Mathematics
Economics
Psychology
Environmental Science
Social Studies
Fashion Studies
English