Trimethylsulfoxonium Iodide1

(X = I)

[1774-47-6]  · C3H9IOS  · Trimethylsulfoxonium Iodide  · (MW 220.09) (X = Cl)

[5034-06-0]  · C3H9ClOS  · Trimethylsulfoxonium Chloride  · (MW 128.64)

(precursor of dimethylsulfoxonium methylide,1 which transfers a methylene group to ketones and aldehydes to form epoxides and to a,b-unsaturated carbonyl compounds to produce cyclopropyl derivatives;1-3 a methylation reagent;4 can function as a catalyst5)

Physical Data: trimethylsulfoxonium iodide: mp 170 °C (dec), yellow crystalline powder; trimethylsulfoxonium chloride: 227 °C (subl), white powder. The vibrational spectra of both iodide and chloride salts, as well as NMR studies of molecular motion of both salts, have been investigated.6-8 pKa = 18.2 for sulfoxonium ion in DMSO.

Solubility: trimethylsulfoxonium iodide: 3.85 g/100 g H2O (20 °C).9 Trimethylsulfoxonium chloride has greater solubility in THF than trimethylsulfoxonium iodide.10 Both sulfoxonium salts sol H2O, DMSO, t-butanol.

Form Supplied in: both iodide and chloride salts are widely available in powder form.

Analysis of Reagent Purity: the purity of trimethylsulfoxonium iodide and trimethylsulfoxonium chloride can be determined by an AgNO3 titration method. A miscible organic solvent, such as acetone, ethanol, or propanol, is usually adopted to carry out the titration process.11 For precise data, the AgNO3(aq) solution should be protected from light and stored in a dark glass bottle.

Purification: trimethylsulfoxonium iodide and trimethylsulfoxonium chloride are precursors of dimethylsulfoxonium methylide. Except when used under phase transfer conditions, the sulfur ylide is usually prepared by deprotonation of trimethylsulfoxonium iodide or trimethylsulfoxonium chloride with moisture-sensitive strong bases such as Sodium Hydride, n-Butyllithium, etc. Therefore drying the salts prior to use is crucial. Trimethylsulfoxonium iodide can be purified by recrystallization from H2O and dried in a desiccator over P2O5 before use.2,9

Preparative Methods: trimethylsulfoxonium iodide is commonly prepared by reaction of Dimethyl Sulfoxide with ~2.5 equiv of Iodomethane.12 After refluxing for 24 h at 80 °C, the reaction mixture is cooled and the crude solid product filtered and washed with acetone to give the trimethylsulfoxonium iodide. Iodomethane has to be handled in a fume hood because of its high volatility and toxicity.12-14 Excess MeI is used to ensure the completion of the reaction.

Trimethylsulfoxonium chloride can be obtained by the treatment of trimethylsulfoxonium iodide with benzyltributylammonium chloride in a mixed solvent system (CH2Cl2/H2O).10 The end point is reached when two clear phases are obtained. The aqueous phase is then washed with CH2Cl2. After evaporation of H2O, solid trimethylsulfoxonium chloride is obtained. Direct oxidation of trimethylsulfonium chloride with Sodium Hypochlorite in the presence of catalytic amount of Ruthenium(VIII) Oxide in H2O at room temperature also provides trimethylsulfoxonium chloride.15 Alternatively, trimethylsulfoxonium chloride can be synthesized by treating a hot aqueous solution of trimethylsulfoxonium iodide with AgCl. After removal of iodide salt, the aqueous filtrate is evaporated to dryness to give trimethylsulfoxonium chloride.6

Handling, Storage, and Precautions: both the iodide and chloride salts are hygroscopic and have to be stored in a cool, dry place. They are incompatible with strong oxidizing agents and strong base. The iodide salt is sensitive to light and needs to be protected from light as much as possible.

Preparation of Dimethylsulfoxonium Methylide.

Trimethylsulfoxonium iodide and trimethylsulfoxonium chloride are primarily utilized in the preparation of Dimethylsulfoxonium Methylide, an extremely useful organic synthesis reagent.


Trimethylsulfoxonium iodide can be converted to Trimethylsulfonium Hydroxide in a mixture of MeOH and water in the presence of Silver(I) Oxide at room temperature. After filtration, the reaction mixture is concentrated and used directly as a methylation reagent. Uracil, thymine, and cytosine were reported to be converted to their corresponding N-methylated products in excellent yield using this reagent. In the same manner, uridine, thymidine, and inosine were smoothly methylated to produce corresponding N-methylated nucleosides.16 Quaternization of tertiary amines is usually accomplished with MeI. Direct treatment of trimethylsulfoxonium iodide with aqueous perchloric acid also provided trimethylsulfoxonium perchlorate, which readily quaternized tertiary amines to their corresponding perchlorate salts in one step.17

Other Usages.

Trimethylsulfoxonium iodide is used as a catalyst in the conversion of oxathiolane to oxathiin in toluene under acidic conditions.5 It is also used in the promotion of the reaction between Phosphorus(V) Sulfide and an alcohol to form the desired dialkyl phosphorodithioic acid.18

1. Corey, E. J.; Chaykovsky, M. JACS 1965, 87, 1353.
2. Corey, E. J.; Chaykovsky, M. OSC 1973, 5, 755.
3. Yamaoka, H.; Mishima, I.; Miyamoto, M.; Hanafusa, T. BCJ 1980, 53, 469.
4. Traynelis, V. J.; McSweeney, J. V. JOC 1966, 31, 243.
5. Znotins, A. A.; Brewer, A. D. U.S. Patent 4 247 707, 1981 (CA 1981, 94, 175 134q).
6. Creighton, J. A.; Green, J. H. S.; Harrison, D. J. Spectrochim. Acta A 1969, 25, 1314.
7. Blaschette, A.; Buerger, H. Inorg. Nucl. Chem. Lett. 1969, 5, 639.
8. Jurga, S.; Jurga, K.; Pajak, Z. J. Phys. C Solid State Phys. 1981, 14, 4433.
9. Perret, R. BSF 1988, 3, 495.
10. Brandstrom, A.; Lamm, B. ACS(B) 1974, 28, 590.
11. (a) Kolthoff, I. M.; Sandell, E. B. Textbook of Quantitative Inorganic Analysis; MacMillan: New York, 1952. (b) Ingram, G. Methods of Organic Elemental Microanalysis; Reinhold: New York, 1962. Method was supplied by Aldrich Chemical Company, Inc.
12. Lampman, G. M.; Koops, R. W.; Olden, C. C. J. Chem. Educ. 1985, 62, 267.
13. Kuhn, R.; Trichmann, H. LA 1958, 611, 177.
14. Irving, E.; Stark, B. P. Br. Polym. J. 1983, 15, 24.
15. Heather, J. B. U.S. Patent 4 625 065, 1986 (CA 1987, 106, 155 583y).
16. Yamauchi, K.; Nakamura, K.; Kinoshita, M. JOC 1978, 43, 1593.
17. Deutsch, E.; Cheung, N. K. V. JOC 1973, 38, 1123.
18. Mirviss, S. B. Eur. Patent 285 073, 1988 (CA 1989, 110, 24 089b).

John S. Ng & Chin Liu

Searle Research and Development, Skokie, IL, USA

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