Fenton's reagent

Fenton's reagent is a solution of hydrogen peroxide with ferrous iron as a 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 (perchloroethylene, PCE). It was developed in the 1890s by Henry John Horstman Fenton as an analytical reagent.[1] [2]

Overview

Iron(II) is oxidized by hydrogen peroxide to iron(III), forming a hydroxyl radical and a hydroxide ion in the process. Iron(III) is then reduced back to iron(II) by another molecule of hydrogen peroxide, forming a hydroperoxyl radical and a proton. 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)

The free radicals generated by this process then engage in secondary reactions. For example, the hydroxyl is a powerful, non-selective oxidant. 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.[3]

Reaction (1) was suggested by Haber and Weiss in the 1930s as part of what would become the Haber–Weiss reaction.[4] Iron(II) sulfate is typically used as the iron catalyst. The exact mechanisms of the redox cycle are uncertain, and non-OH• oxidizing mechanisms of organic compounds have also been suggested. Therefore, it may be appropriate to broadly discuss Fenton chemistry rather than a specific Fenton reaction.

In the electro-Fenton process, hydrogen peroxide is produced in situ from the electrochemical reduction of oxygen.[5]

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.

C6H6 + FeSO4 + H2O2 → C6H5OH

 

 

 

 

(3)

A recent hydroxylation example involves the oxidation of barbituric acid to alloxane.[6] 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.[7]

Biomedical applications

The Fenton reaction has importance in biology because it involves the creation of free radicals by chemicals that are present in vivo. Transition-metal ions such as iron and copper donate or accept free electrons via intracellular reactions and help in creating free radicals. Most intracellular iron is in ferric (+3 ion) form and must be reduced to the ferrous (+2) form to take part in Fenton reaction. Superoxide ions and transition metals act in a synergistic manner in the creation of free radical damage.[8] Therefore, although the clinical significance is still unclear, it is one of the viable reason to avoid iron supplementation in patients with active infections, whereas other reasons include iron-mediated infections.[9]

References

  1. ↑ Fenton H.J.H. (1894). "Oxidation of tartaric acid in presence of iron". J. Chem. Soc., Trans. 65 (65): 899–911. doi:10.1039/ct8946500899.
  2. ↑ Hayyan M., Hashim M.A., AlNashef I.M., Superoxide Ion: Generation and Chemical Implications, Chem. Rev., 2016, 116 (5), pp 3029–3085. DOI: 10.1021/acs.chemrev.5b00407]
  3. ↑ http://geocleanse.com/fentonsreagent.asp
  4. ↑ Haber, F.; Weiss, J. (1932). "Über die Katalyse des Hydroperoxydes". Naturwissenschaften. 20 (51): 948–950. doi:10.1007/BF0150471.
  5. ↑ Juan Casado; Jordi Fornaguera; Maria I. Galan (January 2005). "Mineralization of Aromatics in Water by Sunlight-Assisted Electro-Fenton Technology in a Pilot Reactor". Environ. Sci. Technol. 39 (6): 1843–47. doi:10.1021/es0498787. PMID 15819245.
  6. ↑ Brömme HJ, Mörke W, Peschke E (November 2002). "Transformation of barbituric acid into alloxan by hydroxyl radicals: interaction with melatonin and with other hydroxyl radical scavengers". J. Pineal Res. 33 (4): 239–47. doi:10.1034/j.1600-079X.2002.02936.x. PMID 12390507.
  7. ↑ E. L. Jenner (1973). "α,α,α',α'-Tetramethyltetramethylene glycol". Org. Synth.; Coll. Vol., 5, p. 1026
  8. ↑ Robbins & Cotran (2008). Pathologic Basis of Disease (7th ed.). Elsevier. p. 16. ISBN 9780808923022.
  9. ↑ Lapointe, Marc (2004-01-01). "Iron supplementation in the intensive care unit: when, how much, and by what route?". Critical Care. 8 (2): 1–5. doi:10.1186/cc2825. ISSN 1364-8535. PMC 3226152Freely accessible. PMID 15196322.

Further reading

External links

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