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Trimethylsulfonium (systematically named trimethylsulfanium and trimethylsulfur(1+)) is an organic cation with the chemical formula (CH3)3S+ (also written as C

Preferred IUPAC name
Other names
3D model (JSmol)
  • C[S+](C)C
Molar mass 77.17 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references


Structure of (CH3)3S+ as its tetraphenylborate salt.[1]

Several salts of trimethylsulfonium are known. X-ray crystallography reveals that the sulfur is pyramidal, with C-S-C angles near 102° and C-S bond distance of 177 picometers. Unless the anion is colored, all trimethylsulfonium salts are white or colorless.

Salt Formula Molecular weight (g/mol) Properties[2]
Trimethylsulfonium chloride [(CH3)3S]Cl 112.5 Colorless crystals, decompose at 100 °C, very soluble in ethanol, very hygroscopic.[3]
Trimethylsulfonium bromide [(CH3)3S]Br 157 Colorless crystals from H2O. Decomposes at 172 °C, melts in a sealed tube at 201-201 °C, reacts in neutral aqueous solution.[4]
Trimethylsulfonium iodide [(CH3)3S]I 204 Colorless crystals from ethanol, decomposes at 203-207 °C.[4][5] crystal structure monoclinic a=5.94 b=8.00 c=8.92 μm β=126°32′ 2 formulas per unit cell density=1.958[6]
Trimethylsulfonium tetrafluoroborate [(CH3)3S]BF4 163.97 mp 205-210°[7]
Trimethylsulfonium methylsulfate [(CH3)3S]CH3OSO3 188.27 mp 92-94°[8] Crystal structure orthorhombic a=12.6157 b=8.2419 μm c=7.540 cell volume 784.0 2 formulas per unit cell


Sulfonium compounds can be synthesised by treating a suitable alkyl halide with a thioether. For example, the reaction of dimethyl sulfide with iodomethane yields trimethylsulfonium iodide:

CH3–S–CH3 + CH3–I → (CH3)3SI


An extra oxygen atom can bond to the sulfur atom to yield the trimethylsulfoxonium ion.


Glyphosate herbicide is often supplied as a trimethylsulfonium salt. When mixed with aluminium bromide, or aluminium chloride or even hydrogen bromide, trimethylsulfonium bromide forms an ionic liquid, which melts at temperatures below standard conditions.[9]


  1. ^ Knop, Osvald; Cameron, T. Stanley; Bakshi, Pradip K.; Linden, Antony; Roe, Stephen P. (1994). "Crystal chemistry of tetraradial species. Part 5. Interaction Between Cation Lone Pairs and Phenyl Groups in Tetraphenylborates: Crystal Structures of Me3S+,Et3S+, Me3SO+, Ph2I+, and 1-Azoniapropellane Tetraphenylborates". Canadian Journal of Chemistry. 72 (8): 1870–1881. doi:10.1139/v94-238.
  2. ^ Heilbron's Dictionary of Organic Compounds, volume 4, revised edition published in 1953. Published in Great Britain
  3. ^ Blättler, H. (1919). "Über Trimethylsulfoniumverbindungen". Monatshefte für Chemie und verwandte Teile anderer Wissenschaften. 40 (8): 417–429. doi:10.1007/BF01559085. S2CID 197766904.
  4. ^ a b Steinkopf, W.; Müller, S. (1923). "Über die Einwirkung von Jodmethyl auf Disulfide". Chem. Ber. 56 (8): 1926–1930. doi:10.1002/cber.19230560834.
  5. ^ Mussgnug, F. (1941). "Trimethylammoniumjodid und Trimethylsulfoniumjodid". Naturwissenschaften. 29 (17): 256. Bibcode:1941NW.....29..256M. doi:10.1007/BF01479158. S2CID 33842580.
  6. ^ Zuccaro, D. Ε.; McCullough, J. D. (1 January 1959). "The crystal structure of trimethylsulfonium iodide". Zeitschrift für Kristallographie - Crystalline Materials. 112 (1–6). doi:10.1524/zkri.1959.112.jg.401. S2CID 98338161.
  7. ^ "Trimethylsulfonium tetrafluoroborate". Sigma-Aldrich. Retrieved 23 September 2016. CS1 maint: discouraged parameter (link)
  8. ^ "Trimethylsulfonium methyl sulfate". Sigma-Aldrich. Retrieved 23 September 2016. CS1 maint: discouraged parameter (link)
  9. ^ Ma, M.; Johnson, K.E. (April 1995). "Some physicochemical characteristics of molten salts derived from trimethylsulfonium bromide". Canadian Journal of Chemistry. 73 (4): 593–598. doi:10.1139/v95-076.

See alsoEdit