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Sulfonium ion

A sulfonium ion, also known as sulphonium ion or sulfanium ion, is a positively charged ion (a "cation") featuring three organic substituents attached to sulfur. They have the formula [SR3]+. Together with their negatively charged counterpart, the anion, the compounds are called sulfonium salts.


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

+ CH
+ I

Before the above reaction, the sulfur atom has two lone electron pairs. One of these lone pairs links to the methyl group. At the same time, as part of a concerted nucleophilic substitution mechanism (SN2), the iodide leaving group departs. This leaves a positively charged trimethylsulfonium ion, whose charge is balanced by the iodide. The rate of reaction is even faster with stronger methylating agents, such as methyl trifluoromethanesulfonate.


The compounds are pyramidal at sulfur. Thus Me3S+ is isostructural and isoelectronic to trimethylphosphine. Sulfonium compounds wherein the three substituents differ are chiral and optically stable.[1]

Applications and occurrence[edit]


The sulfonium (more specifically methioninium) species S-adenosylmethionine occurs widely in nature, where it is used as a source of the adenosoyl radical. This radical participates in the biosynthesis of various compounds.[2]

Another, sulfonium (methioninium) species found in nature is S-methylmethionine.

Organic synthesis[edit]

Sulfonium centers stabilize the formation of ylides, which are useful in C-C forming reactions.[3]


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.

See also[edit]


  1. ^ March, J. “Advanced Organic Chemistry” 5th Ed. J. Wiley and Sons, 1992: New York. ISBN 0-471-60180-2.
  2. ^ 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
  3. ^ Mitchell J. Bogdanowicz, Barry M. Trost (1988). "Cyclopropylphenylsulfonium Tetrafluoroborate". Org. Synth. ; Coll. Vol. 6, p. 364 

External links[edit]