Fenton's reagent

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 compounds such as trichloroethylene (TCE) and tetrachloroethylene (PCE).

It was developed in the 1890s by Henry John Horstman Fenton.

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 first suggested by Haber and Weiss in the 1930s, but is commonly referred to as 'the Fenton reaction'. 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 oxigen. [cite journal |author=Juan Casado,Jordi Fornaguera,Maria I. Galan |title=Mineralization of Aromatics in Water by Sunlight-Assisted Electro-Fenton Technology in a Pilot Reactor |journal=Environ. Sci. Technol. |volume=39 |issue=6 |pages=1843–47 |year=2005 |month=January |pmid= |doi= |url=http://pubs.acs.org/cgi-bin/abstract.cgi/esthag/2005/39/i06/abs/es0498787.html]

Fenton's reagent is also used in organic synthesis for the hydroxylation of arenes 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. [cite journal |author=Brömme HJ, Mörke W, Peschke E |title=Transformation of barbituric acid into alloxan by hydroxyl radicals: interaction with melatonin and with other hydroxyl radical scavengers |journal=J. Pineal Res. |volume=33 |issue=4 |pages=239–47 |year=2002 |month=November |pmid=12390507 |doi= |url=http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=0742-3098&date=2002&volume=33&issue=4&spage=239] Another application of the reagent in organic synthesis is in coupling reactions of alkanes. As an example "tert"-butanol is dimerized with Fenton's reagent and sulfuric acid to 2,5-dimethyl-2,5-hexanediol.

The mismanagement of iron in cellular systems can lead to the toxic accumulation of iron in organ systems such as the liver and brain. It is believed that this build up of iron eventually leads to the production of free radicals leading to oxidative stress, cellular damage and eventual cellular death via apoptotic signaling.

External links

* [http://toxics.usgs.gov/definitions/fentons_reagent.html USGS definition]
* [http://www.h2o2.com/applications/industrialwastewater/fentonsreagent.html Reference Library Peroxide Applications]
* Companies that use Fenton's Reagent for chemical remediation: [http://www.orinrt.com ORIN]
* Dimerization of "tert"-butanol in Organic Syntheses [http://www.orgsyn.org/orgsyn/prep.asp?prep=cv5p1026 Online article]

References

*cite journal
title = Oxidation of tartaric acid in presence of iron
author = Fenton H.J.H.
journal = J. Chem. Soc., Trans.
volume = 65
issue = 65
pages = 899–911
year = 1894
doi = 10.1039/CT8946500899

*cite journal
title = The Fenton reagents
author = Goldstein Sara, Meyerstein Dan, and Czapski Gidon
journal = Free Radical Biology and Medicine
volume = 15
issue = 4
pages = 435–445
year = 1993
doi = 10.1016/0891-5849(93)90043-T

Haber, F. and Weiss, J. (1932). Uber die Katalyse des Hydroperoxydes.Naturwissenschaften 20, 948–950.