Trimethylsulfoxonium iodide is a sulfoxonium salt derived from dimethylsulfoxide.

It is iodide salt of a common sulfoxonium ions.

It may be prepared by the alkylation of dimethyl sulfoxide with iodomethane:[1] The trimethylsulfoxonium ion features a tetrahedral sulfur center.

Trimethylsulfoxonium iodide is used to generate dimethyloxosulfonium methylide by reaction with sodium hydride.

[2] The latter compound is used to prepare epoxides from ketones and aldehydes.