Fenton's reagent
Encyclopedia
Fenton's reagent is a solution of hydrogen peroxide
and an iron
catalyst that is used to oxidize contaminants or waste waters. Fenton's reagent can be used to destroy organic compound
s such as trichloroethylene
(TCE) and tetrachloroethylene
(PCE).
It was developed in the 1890s by Henry John Horstman Fenton
as an analytical reagent.
Ferrous
Iron(II) is oxidized by hydrogen peroxide to ferric
iron(III), a hydroxyl radical
and a hydroxyl
anion. Iron(III) is then reduced back to iron(II), a peroxide radical and a proton
by the same hydrogen peroxide (disproportionation
).
(1) Fe2+ + H2O2 → Fe3+ + OH· + OH−
(2) Fe3+ + H2O2 → Fe2+ + OOH· + H+
Reaction (1) was suggested by Haber
and Weiss in the 1930s,. In the net reaction the presence of iron is truly catalytic and two molecules of hydrogen peroxide are converted into two hydroxyl radicals and water. The generated radicals then engage in secondary reactions. Iron(II) sulfate
is a typical iron compound in Fenton's reagent. The exact mechanisms are debated (also non-OH· oxidizing mechanisms of organic compounds have been suggested) and, therefore, it may be appropriate to broadly discuss 'Fenton chemistry' rather than a 'Fenton reaction'.
In the Electro-Fenton process, hydrogen peroxide is produced in the required amount from the electrochemical reduction of oxygen.
Fenton's reagent is also used in organic synthesis
for the hydroxylation
of arene
s in a radical substitution
reaction such as the classical conversion of benzene
into phenol
.
(3) C6H6 + FeSO4 + H2O2 → C6H5OH
A recent hydroxylation example involves the oxidation of barbituric acid
to alloxane. Another application of the reagent in organic synthesis is in coupling reaction
s of alkanes. As an example tert-butanol
is dimerized with Fenton's reagent and sulfuric acid
to 2,5-dimethyl-2,5-hexanediol.
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
and an iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
catalyst that is used to oxidize contaminants or waste waters. Fenton's reagent can be used to destroy organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
s such as trichloroethylene
Trichloroethylene
The chemical compound trichloroethylene is a chlorinated hydrocarbon commonly used as an industrial solvent. It is a clear non-flammable liquid with a sweet smell. It should not be confused with the similar 1,1,1-trichloroethane, which is commonly known as chlorothene.The IUPAC name is...
(TCE) and tetrachloroethylene
Tetrachloroethylene
Tetrachloroethylene, also known under its systematic name tetrachloroethene and many other names, is a chlorocarbon with the formula Cl2C=CCl2. It is a colourless liquid widely used for dry cleaning of fabrics, hence it is sometimes called "dry-cleaning fluid." It has a sweet odor detectable by...
(PCE).
It was developed in the 1890s by Henry John Horstman Fenton
Henry John Horstman Fenton
Henry John Horstman Fenton was a British chemist who, in the 1890s invented Fenton's reagent, a solution of hydrogen peroxide and an iron catalyst that is used to oxidize contaminants or waste waters...
as an analytical reagent.
Ferrous
Ferrous
Ferrous , in chemistry, indicates a divalent iron compound , as opposed to ferric, which indicates a trivalent iron compound ....
Iron(II) is oxidized by hydrogen peroxide to ferric
Ferric
Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron or Fe3+. On the other hand, ferrous refers to iron with oxidation number of +2, denoted iron or Fe2+...
iron(III), a hydroxyl radical
Hydroxyl radical
The hydroxyl radical, •OH, is the neutral form of the hydroxide ion . Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry. Most notably hydroxyl radicals are produced from the decomposition of hydroperoxides or, in...
and a hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
anion. Iron(III) is then reduced back to iron(II), a peroxide radical and a proton
Hydrogen atom
A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively-charged proton and a single negatively-charged electron bound to the nucleus by the Coulomb force...
by the same hydrogen peroxide (disproportionation
Disproportionation
Disproportionation, also known as dismutation is used to describe a specific type of redox reaction in which a species is simultaneously reduced and oxidized so as to form two different products....
).
(1) Fe2+ + H2O2 → Fe3+ + OH· + OH−
(2) Fe3+ + H2O2 → Fe2+ + OOH· + H+
Reaction (1) was suggested by Haber
Fritz Haber
Fritz Haber was a German chemist, who received the Nobel Prize in Chemistry in 1918 for his development for synthesizing ammonia, important for fertilizers and explosives. Haber, along with Max Born, proposed the Born–Haber cycle as a method for evaluating the lattice energy of an ionic solid...
and Weiss in the 1930s,. In the net reaction the presence of iron is truly catalytic and two molecules of hydrogen peroxide are converted into two hydroxyl radicals and water. The generated radicals then engage in secondary reactions. Iron(II) sulfate
Iron(II) sulfate
Iron sulfate or ferrous sulfate is the chemical compound with the formula FeSO4. Known since ancient times as copperas and as green vitriol, the blue-green heptahydrate is the most common form of this material...
is a typical iron compound in Fenton's reagent. The exact mechanisms are debated (also non-OH· oxidizing mechanisms of organic compounds have been suggested) and, therefore, it may be appropriate to broadly discuss 'Fenton chemistry' rather than a 'Fenton reaction'.
In the Electro-Fenton process, hydrogen peroxide is produced in the required amount from the electrochemical reduction of oxygen.
Fenton's reagent is also used in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
for the hydroxylation
Hydroxylation
Hydroxylation is a chemical process that introduces a hydroxyl group into an organic compound. In biochemistry, hydroxylation reactions are often facilitated by enzymes called hydroxylases. Hydroxylation is the first step in the oxidative degradation of organic compounds in air...
of arene
Arene
Arene or Arênê or Arène may refer to:*an aromatic hydrocarbon*Arene , a genus of marine snails in the family Areneidae*Arene , the wife of Aphareus and mother of Idas and Lynceus in Greek mythology...
s in a radical substitution
Radical substitution
In organic chemistry, a radical substitution reaction is a substitution reaction involving free radicals as a reactive intermediate.The reaction always involves at least two steps, and possibly a third....
reaction such as the classical conversion of benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
into phenol
Phenol
Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
.
(3) C6H6 + FeSO4 + H2O2 → C6H5OH
A recent hydroxylation example involves the oxidation of barbituric acid
Barbituric acid
Barbituric acid or malonylurea or 6-hydroxyuracil is an organic compound based on a pyrimidine heterocyclic skeleton. It is an odorless powder soluble in water. Barbituric acid is the parent compound of barbiturate drugs, although barbituric acid itself is not pharmacologically active...
to alloxane. Another application of the reagent in organic synthesis is in coupling reaction
Coupling reaction
A coupling reaction in organic chemistry is a catch-all term for a variety of reactions where two hydrocarbon fragments are coupled with the aid of a metal catalyst...
s of alkanes. As an example tert-butanol
Tert-Butanol
tert-Butanol, or 2-methyl-2-propanol, is the simplest tertiary alcohol. It is one of the four isomers of butanol. tert-Butanol is a clear liquid with a camphor-like odor. It is very soluble in water and miscible with ethanol and diethyl ether...
is dimerized with Fenton's reagent and sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
to 2,5-dimethyl-2,5-hexanediol.
Further reading
- K. Barbusinsky (2009) Ecological Chemistry and Engineering vol 16 no 3 pp 347-358 "Fenton Reaction - Controversy concerning the chemistry"
External links
- USGS definition
- Reference Library Peroxide Applications
- Companies that use Fenton's Reagent for chemical remediation: ORIN