Trimethylsulfonium (systematically named trimethylsulfanium) is an organic cation with the chemical formula (also written as).
Several salts of trimethylsulfonium are known. X-ray crystallography reveals that the ion has trigonal pyramidal molecular geometry at sulfur atom, with C-S-C angles near 102° and C-S bond distance of 177 picometers. Unless the counteranion is colored, all trimethylsulfonium salts are white or colorless.
| Salt | Formula | Molecular weight (g/mol) | Properties[1] |
|---|---|---|---|
| Trimethylsulfonium chloride | 112.5 | Colorless crystals, decompose at 100 °C, very soluble in ethanol, very hygroscopic.[2] | |
| Trimethylsulfonium bromide | 157 | Colorless crystals. Decomposes at 172 °C, melts in a sealed tube at 201-201 °C, reacts in neutral aqueous solution.[3] | |
| Trimethylsulfonium iodide | 204 | Colorless crystals, decomposes at 203-207 °C.[4] crystal structure monoclinic, with these parameters: a = 5.94 μm, b = 8.00 μm, c = 8.92 μm, β = 126°32′ 2 formulas per unit cell, density = 1.958 g/cm3[5] | |
| Trimethylsulfonium tetrafluoroborate | 163.97 | melting point = 205-210 °C[6] | |
| Trimethylsulfonium methylsulfate | 188.27 | melting point = 92-94 °C[7] Crystal structure orthorhombic with these parameters: a = 12.6157 μm, b = 8.2419 μm, c = 7.540 μm 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:
An extra oxygen atom can bond to the sulfur atom to yield the trimethylsulfoxonium ion, where the sulfur atom is tetravalent and tetracoordinated.
Glyphosate herbicide is often supplied as a trimethylsulfonium salt, referred to as trimesium.[8]
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]