Sulfonium

A sulfonium ion, or sulphonium 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&minus; (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 (SN2), 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.