Fenton's reagent

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Fenton reaction
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Fenton's reagent is a solution of

waste water as part of an advanced oxidation process. Fenton's reagent can be used to destroy organic compounds such as trichloroethylene and tetrachloroethylene (perchloroethylene). It was developed in the 1890s by Henry John Horstman Fenton as an analytical reagent.[2][3][4]

Reactions

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.[5]

Fe2+ + H2O2 → Fe3+ + HO• + OH−

 

 

 

 

(1)

Fe3+ + H2O2 → Fe2+ + HOO• + H+

 

 

 

 

(2)

2 H2O2 → HO• + HOO• + H2O

 

 

 

 

(net reaction: 1+2)

The

exothermic
and results in the oxidation of contaminants to primarily carbon dioxide and water.

Reaction (1) was suggested by Haber and Weiss in the 1930s as part of what would become the Haber–Weiss reaction.[7]

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.[citation needed] 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.[8]

Fenton's reagent is also used in

arenes in a radical substitution reaction such as the classical conversion of benzene into phenol
.

C6H6 + FeSO4 + H2O2 → C6H5OH + (byproducts)

 

 

 

 

(3)

An example hydroxylation reaction involves the

tert-butanol is dimerized with Fenton's reagent and sulfuric acid to 2,5-dimethyl-2,5-hexanediol.[10] Fenton's reagent is also widely used in the field of environmental science for water purification and soil remediation. Various hazardous wastewater were reported to be effectively degraded through Fenton's reagent.[11]

Effect of pH on formation of free radicals

Fe(OH)3, lowering the concentration of the Fe+3 species in solution.[11] Solubility of iron species is directly governed by the solution's pH. Fe+3 is about 100 times less soluble than Fe+2 in natural water at near-neutral pH, the ferric ion concentration is the limiting factor for the reaction rate. Under high pH conditions, the stability of the H2O2 is also affected, resulting in its self-decomposition.[14] Higher pH also decreased the redox potential of •OH thereby reducing its effectiveness.[15] pH plays a crucial role in the formation of free radicals and hence the reaction performance. Thus ongoing research has been done to optimize pH and amongst other parameters for greater reaction rates.[16]

Impacts of operation pH on reaction rate
Low pH Formation of [Fe(H2O)6]2+ complex, hence reducing Fe2+ for radical generation
Scavenging of •OH by excess H+
High pH Lower redox potential of •OH
Self-decomposition of H2O2 due to decreased stability at high pH
Precipitation of Fe(OH)3 species in solution

Biomedical implications

The Fenton reaction has different implications in biology because it involves the formation of free radicals by chemical species naturally present in the cell under

free radicals. Superoxide ions and transition metals act in a synergistic way in the appearance of free radical damages.[18] Therefore, although the clinical significance is still unclear, it is one of the viable reasons to avoid iron supplementation in patients with active infections, whereas other reasons include iron-mediated infections.[19]

Applications

See also: Advanced oxidation process

Fenton's reagent is used as a sewage treatment agent.[20]

Fenton's reagent can be used in different chemical procesess that supply hydroxyl ion or oxidize certain compounds:[21]

Fenton-like reagent

Mixtures of Fe+2 and H2O2 are called Fenton reagent. If Fe+2 is replaced by Fe+3, it is called Fenton-like reagent.

Numerous transition metal ions and their complexes in their lower oxidation states (LmMn+) were found to have the oxidative features of the Fenton reagent, and, therefore, the mixtures of these metal compounds with H2O2 were named "Fenton-like" reagents.[22]

See also

References

  1. ISBN 9780123982568
    .
  2. PMID 8138191
    .
  3. doi:10.1039/ct8946500899
    .
  4. PMID 26875845
    .
  5. S2CID 231712587
    .
  6. S2CID 224976088
    .
  7. S2CID 40200383
    .
  8. PMID 15819245
    .
  9. S2CID 30242100
    .
  10. ^ Jenner, E. L. (1973). "α,α,α′,α′-Tetramethyltetramethylene glycol". Organic Syntheses; Collected Volumes, vol. 5, p. 1026.
  11. ^
    S2CID 227523802
    .
  12. doi:10.1016/j.seppur.2009.05.013
    .
  13. doi:10.1080/09593330.1996.9618465
    .
  14. PMID 11358291
    .
  15. doi:10.1002/aic.15369
    .
  16. S2CID 234110033
    .
  17. S2CID 3918519
    .
  18. ISBN 978-0-8089-2302-2
    .
  19. PMID 15196322
    .
  20. ISSN 2071-1050
    .
  21. ^ "Fenton's Reaction - Reaction Details, Reagent, Applications, FAQs". BYJUS. Retrieved 2022-07-25.
  22. PMID 8225025
    . Retrieved 19 November 2023.

Further reading

External links

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