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Sulfenic acid

A sulfenic acid is an organosulfur compound and oxoacid with the general formula R S O H. It is the first member of the family of organosulfur oxoacids, which also include sulfinic acids and sulfonic acids, R S O2 H and R S O3 H, 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 ( rotational spectroscopy) to be CH3–S–O–H. Sulfenic acids can be stabilized through steric effects, which prevent the sulfenic acid from condensing with itself to form thiosulfinates, RS(O)SR, such as allicin from garlic. Through the use of X-ray crystallography, the structure of such stabilized sulfenic acids were shown to be R–S–O–H. The stable, sterically hindered sulfenic acid, 1-triptycenesulfenic acid, has been found to have a 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, R O O H.

Formation and occurrence

In nature

Sulfenic acids are produced by the enzymatic decomposition of alliin and related compounds following tissue damage to garlic, onions, and other plants of the Allium genus. 1-Propenesulfenic acid, formed when onions are cut, is rapidly rearranged by a second enzyme, the lachrymatory factor synthase, giving syn-propanethial-S-oxide. 2-Propenesulfenic acid, formed from allicin, is thought to be responsible for garlic’s potent antioxidant activity. Mass spectrometry with a 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. The pharmacological activity of certain drugs, such as omeprazole, esomeprazole, ticlopidine, clopidogrel, and prasugrel is proposed to involve sulfenic acid intermediates. Oxidation of cysteine residues in protein to the corresponding protein sulfenic acids is suggested to be important in redox-mediated signal transduction. 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.

Organic chemistry

The conversion of certain sulfoxides to alkenes proceeds via the elimination of sulfenic acid: RS(O)CH2CH2R′ → RSOH + CH2=CHR′

Other sulfenyl compounds

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 methane sulfenyl chloride, CH3SCl.IUPAC Gold Book http://goldbook.iupac.org/goldbook/S06098.html Sulfenate esters, which have the formula RSOR′, are intermediates in the Mislow-Evans rearrangement of allyl sulfoxides.Braverman, S., "Rearrangements involving sulfenic acids and their derivatives," in Sulfenic Acids and Derivatives, 1990, John Wiley & Sons. Sulfenamides have the formula RSNR′2.

References

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This article based upon the http://en.wikipedia.org/wiki/Sulfenic_acid, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Sulfenic_acid&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany