A sulfonium ion, also known as sulphonium ion and sulfanium ion, is a positively charged sulfur ion carrying three alkyl groups as substituents (S⁺R₃). Ionic compounds consisting of a positively charged sulfonium cation and a negatively charged anion are called sulfonium salts.

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

CH₃–S–CH₃ + CH₃–I → (CH₃)₃S⁺ + I⁻

In the above reaction, the alkylation of a sulfide, the sulfur atom has two lone electron pairs. Using those lone pairs, the sulfide acts as a nucleophile, and attacks the carbon of iodomethane. At the same time, as part of a concerted nucleophilic substitution mechanism (S_N2), the iodide leaving group comes off; this leaves a positively charged trimethylsulfonium ion. This cation is attracted to the negatively charged iodide, so the two form an ionic bond, giving trimethylsulfonium iodide.

[edit] See also

• Sulfide R-S-R
• Sulfate R-SO₄-R
• Sulfite R-SO₃-R
• Sulfonate R-SO₃⁻
• Onium compounds

[edit] External links

• IUPAC definition (short pdf)

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