Trimethylsulfonium Iodide

Me3S+X-
(X = I)

[2181-42-2]  · C3H9IS  · Trimethylsulfonium Iodide  · (MW 204.09) (X = Br)

[3084-53-5]  · C3H9BrS  · Trimethylsulfonium Bromide  · (MW 157.09)

(precursor of dimethylsulfonium methylide1)

Physical Data: Me3SI, mp 211-212.5 °C (dec); Me3SBr, mp 201-202 °C (dec, sealed tube), 172 °C (dec).

Solubility: sol H2O, alcohol, THF, DMSO.

Form Supplied in: Me3SI, white crystals; Me3SBr, white deliquescent crystals.

Preparative Methods: Me3SI is prepared in almost quantitative yield by mixing equimolar amounts of Dimethyl Sulfide and Iodomethane at room temperature. After standing overnight, the resulting solid white cake is crushed and recrystallized from absolute ethanol to give pure trimethylsulfonium iodide.1b,2

To prepare Me3SBr, a mixture of Me2S and an excess amount (more than 3.0 equiv) of Bromomethane is heated at 100 °C for 4 h in a sealed tube. During workup the contents of the tube give out a strong irritating odor. The resulting white crystals are washed with ethyl acetate and recrystallized from a small amount of water to give white, deliquescent crystals of trimethylsulfonium bromide.2a

Handling, Storage, and Precautions: irritant.

Formation of Dimethylsulfonium Methylide.

Treatment of trimethylsulfonium iodide (or bromide) with strong bases such as the methylsulfinyl carbanion1b,3 (Potassium t-Butoxide in Dimethyl Sulfoxide, Sodium Hydride in DMSO-THF, Sodium Ethoxide in DMSO) or n-Butyllithium in THF gave a solution of Dimethylsulfonium Methylide. This heat-labile reagent generated in situ is an exceedingly selective methylene-transfer reagent which is of great use for converting carbonyl compounds into epoxides (even in the case of a,b-unsaturated carbonyl compounds).4 This ylide also converts imines to aziridines.


1. (a) Corey, E. J.; Chaykovsky, M. JACS 1962, 84, 3782. (b) Corey, E. J.; Chaykovsky, M. JACS 1965, 87, 1353. (c) Franzen, V.; Driesen, H. E. TL 1962, 661. (d) Franzen, V.; Driesen, H. E. CB 1963, 96, 1881.
2. (a) Steinkopf, W.; Müller, S. CB 1923, 56, 1926. (b) Emeléus, H. J.; Heal, H. G. JCS 1946, 1126. (c) Swain, C. G.; Kaiser, L. E. JACS 1958, 80, 4089.
3. Corey, E. J.; Chaykovsky, M. JACS 1962, 84, 866.
4. Rosenberger, M.; Jackson, W.; Saucy, G. HCA 1980, 63, 1665.

Renji Okazaki & Norihiro Tokitoh

The University of Tokyo, Japan



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