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:

CH₃-S-CH₃ + CH₃-I → (CH₃)₃S⁺ I⁻ (trimethylsulfonium iodide)

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.

See also

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

References

External links

• IUPAC definition (short pdf)