Fenton's reagent is a solution of hydrogen peroxide and ferrous ion that generates hydroxyl radicals and is used to oxidize organic compounds. It consists of iron(II) sulfate and hydrogen peroxide and causes the disproportionation of hydrogen peroxide through a redox cycle to produce hydroxyl and hydroperoxyl radicals. These radicals then engage in secondary reactions to rapidly oxidize contaminants into carbon dioxide and water. Some applications of Fenton's reagent include the hydroxylation of arenes like benzene to phenol, converting barbituric acid to the toxic compound alloxan, and oxidizing glycerol to a mixture of glyceraldehyde and dihydroxyacetone known as glycerose.

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6. Fenton’s Reagent

2. …Fenton’s Reagent
Ø Fenton's reagent is a solution of hydrogen peroxide (H2O2) with ferrous ion
(typically iron(II)sulfate, FeSO4) as a catalyst that is used to oxidize
contaminants or waste waters.
Ø Fenton's reagent can be used to destroy organic compounds such
as trichloroethylene (TCE) and tetrachloroethylene (perchloroethylene, PCE).
Ø It was developed in the 1890s by British Chemist Henry John Horstman
Fenton as an analytical reagent.
FeSO4 + H2O2

3. …Fenton’s Reagent
Ø Iron(II) is oxidized by hydrogen peroxide to iron(III), forming a hydroxyl radical and a
hydroxide ion in the process.
Ø Iron(III) is then reduced back to iron(II) by another molecule of hydrogen peroxide,
forming a hydroperoxyl radical and a proton.
Ø The net effect is a disproportionation of hydrogen peroxide to create two different
oxygen-radical species, with water (H+ + OH−) as a byproduct.
Fe2+ + H2O2 → Fe3+ + HO• + OH− (1)
Fe3+ + H2O2 → Fe2+ + HOO• + H+ (2)
2 H2O2 → HO• + HOO• + H2O (net reaction: 1+2)
Reaction (1) was suggested by Haber and Weiss in the 1930s as part of what would
become the Haber–Weiss reaction.
FeSO4 + H2O2

4. …Fenton’s Reagent
Ø The free radicals generated by this process then engage in secondary reactions.
For example, the hydroxyl is a powerful, non-selective oxidant.
Ø Oxidation of an organic compound by Fenton's reagent is rapid and
exothermic and results in the oxidation of contaminants to primarily carbon
dioxide and water.
Ø Iron(II) sulfate is typically used as the iron catalyst. The exact mechanisms
of the redox cycle are uncertain.
FeSO4 + H2O2

5. …Fenton’s Reagent: Applications
1. Fenton's reagent is used in organic synthesis for the hydroxylation of arenes
in a radical substitution reaction such as the classical conversion of benzene into
phenol.
C6H6 + FeSO4 + H2O2 → C6H5OH
Fe2+ + H2O2 → Fe3+ + HO• + OH−
Mechanism:
FeSO4 + H2O2

6. …Fenton’s Reagent
2. Transformation of barbituric acid into alloxan by hydroxyl radicals
J. Pineal Res. 2002; 33:239–247
Barbituric acid is based on a pyrimidine
heterocycle.
It is the parent compound of barbiturate drugs.
Alloxan is a toxic glucose analogue, which
selectively destroys insulin-producing cells in
the pancreas (i.e., beta cells) when administered
to rodents and many other animal species.
FeSO4 + H2O2

7. …Fenton’s Reagent
3. Glycerol on oxidation with Fenton’s reagent (H2O2 + FeSO4)
gives a mixture of glyceraldehyde & dihydroxyacetone. Mixture of
these two are known as Glycerose.
FeSO4 + H2O2

8. …Fenton’s Reagent
4. Conversion of tartaric acid into dihydroxy fumaric acid;
Ø Tartaric acid is a white, crystalline organic acid that occurs naturally in many
fruits, most notably in grapes, but also in bananas, and citrus.
Ø Its salt, potassium bitartrate, commonly known as cream of tartar, develops
naturally in the process of winemaking.
FeSO4 + H2O2

9. …Fenton’s Reagent
5. Hydroxylation of salicylic acid in aqueous medium by the
electrogeneration of Fenton’s reagent: An attack of hydroxyl radical on
salicylic acid produced 2,3- and 2,5-dihydroxybenzoic acids with 2,3-
dihydroxy-benzoic acid as a major product.
New J. Chem., 2012, 36, 1265–1272
FeSO4 + H2O2

10. …Fenton’s Reagent: Summary
1. Hydroxylation of arenes.
2. Barbituric acid into alloxan.
3. Glycerol gives a mixture of glyceraldehyde & dihydroxyacetone
~ known as Glycerose.
4. Tartaric acid into dihydroxy fumaric acid.
5. Hydroxylation of salicylic acid.
FeSO4 + H2O2