Sulfonium

File:Dimethylsulfoniopropionate Structural Formula V1.svg (DMSP), is found in marine phytoplankton and seaweeds.{{Cite journal|last=DeBose|first=Jennifer L.|author2=Sean C. Lema|author3=Gabrielle A. Nevitt|date=2008-03-07|title=Dimethylsulfoniopropionate as a foraging cue for reef fishes|journal=Science|volume=319|issue=5868|pages=1356|doi=10.1126/science.1151109|pmid=18323445|bibcode=2008Sci...319.1356D|s2cid=20782786|url=https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1339&context=bio_fac}}]]

Sulfonium compounds are usually synthesized by the reaction of thioethers with alkyl halides. For example, the reaction of dimethyl sulfide with iodomethane yields trimethylsulfonium iodide:

: {{chem2|CH3SCH3 + CH3I -> (CH3)3S+I-}}

The reaction proceeds by a nucleophilic substitution mechanism (S_N2), where iodide is the leaving group. For weakly electrophilic alkyl halides, the reactions can be accelerated by the addition of silver tetrafluoroborate. In that vein, the rate (and irreversibility) of methylation improves with more electrophilic methylating agents such as methyl trifluoromethanesulfonate.

These S-alkylations can be reversible, especially when the leaving group is iodide. For example, alkylation of dimethylsulfide with allyl iodide gives trimethylsulfonium iodide. In a related process, secondary alkyl halides react with dimethylsulfide to give mixed thioether, eliminating methyl halide.{{cite book |doi=10.1002/9780470771648.ch11 |chapter=Synthesis of Sulphonium Salts |title=The Sulfonium Group: Vol. 1 (1981) |date=1981 |last1=Lowe |first1=P. A. |pages=267–312 |isbn=978-0-470-77164-8|series=PATAI's Chemistry of Functional Groups }}

Below are listed some other synthetic methods, among many:

• sulfonium salts can be made by treating secondary and tertiary alcohols with sulfuric acid in the presence of thioethers.
• addition of methyl iodide to dimethyldisulfide in the presence of a mercuric halide catalyst.
• addition of sulfenyl chlorides to alkenes, giving episulfonium salts.
• alkylation of thioethers with electrophilic alkenes in the presence of a proton donor.

Sulfonium ions with three different substituents are chiral owing to their pyramidal structure. Unlike the isoelectronic oxonium ions (R₃O⁺), chiral sulfonium ions are resolvable into optically stable enantiomers.March, J. "Advanced Organic Chemistry" 5th Ed. J. Wiley and Sons, 1992: New York. {{ISBN|0-471-60180-2}} [Me(Et)SCH₂CO₂H]⁺ is the first chiral sulfonium cation to be resolved into enantiomers.{{cite book |doi=10.1016/B978-0-12-507704-0.50007-6|title=Asymmetric Synthesis|year=1984|pages=227–261|chapter=Optical Activation and Utilization of Compounds Containing Chiral Sulfur Centers

|first1=Michael R.|last1=Barbachyn|first2=Carl R.|last2=Johnson|isbn=9780125077040}} The barrier to inversion ranges from 100 to 130 kJ/mol.

The sulfonium (more specifically methioninium) species S-adenosylmethionine occurs widely in nature, where it is used as a source of the adenosoyl or methyl radicals. These radicals participate in the biosynthesis of many compounds.Layer, G.; Heinz, D. W.; Jahn, D.; Schubert, W.-D. "Structure and function of radical SAM enzymes" Current Opinion in Chemical Biology 2004, volume 8, 468-476. {{doi|10.1016/j.cbpa.2004.08.001}}Perry A. Frey, Olafur Th. Magnusson "S-Adenosylmethionine:  A Wolf in Sheep's Clothing, or a Rich Man's Adenosylcobalamin?" Chem. Rev., 2003, 103 (6), pp 2129–2148. {{doi|10.1021/cr020422m}}

Image:S-Adenosyl-L-methionin.svg.]]

Other naturally-occurring sulfonium species are S-methylmethionine (methioninium) and the related dimethylsulfoniopropionate (DMSP).

Sulfonium salts are precursor to sulfur ylides, which are useful in carbon–carbon bond-forming reactions. In a typical application, a R₂S⁺CH₂{{prime|R}} center is deprotonated to give the ylide R₂S⁺CHR⁻.{{OrgSynth | author = Mitchell J. Bogdanowicz, Barry M. Trost | title = Cyclopropylphenylsulfonium Tetrafluoroborate | volume = 54 | pages = 27 | doi = 10.15227/orgsyn.054.0027 | year = 1974}} These ylides add to ketones and aldehydes to give epoxides (Johnson–Corey–Chaykovsky reaction).{{cite journal |doi=10.1021/acs.chemrev.9b00111 |title=Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts |date=2019 |last1=Kaiser |first1=Daniel |last2=Klose |first2=Immo |last3=Oost |first3=Rik |last4=Neuhaus |first4=James |last5=Maulide |first5=Nuno |journal=Chemical Reviews |volume=119 |issue=14 |pages=8701–8780 |pmid=31243998 |pmc=6661881 }}

Image:TASF.png.]]

Tris(dimethylamino)sulfonium difluorotrimethylsilicate [((CH₃)₂N)₃S]⁺[F₂Si(CH₃)₃]⁻ is a popular fluoridation agent.{{OrgSynth | author = W. J. Middleton | title = Tris(dimethylamino)sulfonium difluorotrimethylsilicate | volume = 64 | pages = 221 | year = 1986 | doi = 10.15227/orgsyn.064.0221}}

Some azo dyes are modified with sulfonium groups to give them a positive charge. The compound triphenylsulfonium triflate is a photoacid, a compound that under light converts to an acid.{{cn|date=November 2024}}

Organic sulfides react with liquid bromine to give bromosulfonium bromides, i.e.:{{cite book|title=Sulfur in Organic and Inorganic Chemistry|volume=1|editor-first=Alexander|editor-last=Senning|year=1971|publisher=Marcel Dekker|location=New York|lccn=70-154612|isbn=0-8247-1615-9|first=Philip S.|last=Magee|chapter=The Sulfur–Bromine Bond|pages=316–321}}

:RS{{prime|R}} + [R{{prime|R}}S⁺Br]Br⁻

• Onium compounds

• [https://goldbook.iupac.org/terms/view/S06121 IUPAC definition] (short pdf)

Category:Cations

Category:Sulfur ions