Sulfenic acid

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tautomerism
, spectroscopic measurements as well as theoretical studies indicate that the structure on the left predominates almost exclusively.

In

oxoacid with the general formula R−S−OH. It is the first member of the family of organosulfur oxoacids, which also include sulfinic acids (R−S(=O)OH) and sulfonic acids (R−S(=O)2OH), respectively. The base member of the sulfenic acid series with R = H is hydrogen thioperoxide
.

Properties

In contrast to sulfinic and sulfonic acids, simple sulfenic acids, such as methanesulfenic acid, CH3SOH, are highly reactive and cannot be isolated in solution. In the gas phase the lifetime of methanesulfenic acid is about one minute. The gas phase structure of methanesulfenic acid was found by microwave spectroscopy (

pKa of 12.5 and an O–H bond-dissociation energy (bde) of 71.9 ± 0.3 kcal/mol, which can be compared to a pKa of ≥14 and O–H BDE of ~88 kcal/mol for the (valence) isoelectronic hydroperoxides, ROOH.[4]

Formation and occurrence

Peroxiredoxins

Peroxiredoxins are ubiquitous and abundant enzymes that detoxify peroxides. They function by the conversion of a cysteine residue to a sulfenic acid. The sulfenic acid then converts to a disulfide by reaction with another residue of cysteine.[5]

Garlic and onions

Sulfenic acids are produced by the enzymatic decomposition of

DART ion source were used to identify 2-propenesulfenic formed when garlic is cut or crushed and to demonstrate that this sulfenic acid has a lifetime of less than one second.[8] The pharmacological activity of certain drugs, such as omeprazole, esomeprazole, ticlopidine, clopidogrel, and prasugrel is proposed to involve sulfenic acid intermediates.[9] Oxidation of cysteine residues in protein to the corresponding protein sulfenic acids is suggested to be important in redox-mediated signal transduction.[10][11]

Sulfenic acid forms part of the series of chemical reactions that occur when cutting onions. The lachrymal glands are irritated by the end product of the reactions, syn-Propanethial-S-oxide, causing tears.[12]

Organic and inorganic chemistry

Dioctadecyl 3,3'-thiodipropanoate: Oxidation to the sulfoxide and subsequent Ei elimination generates a sulfenic acid. This material is used as a polymer stabilizer where it protects against long term heat ageing

Sulfoxides can undergo thermal elimination via an Ei mechanism to yield vinyl alkenes and sulfenic acids:[13][14]

Compounds which react in this manner are used as

polymer stabilizers where they protects against long term heat ageing,[15] structures based on thiodipropionate esters are popular.[16]

Sulfenate-based ligands are found at the active site of the nitrile hydratases. The S=O group is proposed as the nucleophile that attacks the nitrile.[17]

Other sulfenyl compounds

Cyclohexylthiophthalimide is an example of a sulfenamide, yet another derivative of sulfenic acid.

The prefix sulfenyl in organic nomenclature denotes the RS group (R ≠ H). One example is methanesulfenyl chloride, CH3SCl.[18]


Sulfenate esters have the formula RSOR′. They arise by the reaction of sulfenyl chlorides on alcohols.

Mislow-Evans rearrangement of allyl sulfoxides.[13]
Sulfenamides have the formula RSNR′2.

References

  1. doi:10.1021/ja00479a068
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  3. doi:10.1021/ja962995k
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  4. PMID 21049943
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  5. PMID 28226215
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  6. ISBN 978-0-85404-190-9
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  7. PMID 19040240
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  8. PMID 20225897
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  9. PMID 20869346
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  10. PMID 20845928.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  11. PMID 23748139
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  12. ^ "Why does chopping an onion make you cry?". Everyday Mysteries. The Library of Congress. Retrieved 1 April 2019.
  13. ^
    doi:10.1002/9780470772287.ch8
  14. doi:10.15227/orgsyn.070.0029.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  15. ISBN 978-0-12-803581-8
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  16. doi:10.1016/0014-3057(75)90141-X
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  17. PMID 15096062
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  18. doi:10.1351/goldbook.S06098
  19. doi:10.15227/orgsyn.081.0244
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