Trimethylsulfonium

Trimethylsulfonium is an organic cation with the chemical formula .

Compounds

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	Properties
Trimethylsulfonium chloride		112.5	Colorless crystals, decompose at 100 °C, very soluble in ethanol, very hygroscopic.
Trimethylsulfonium bromide		157	Colorless crystals. Decomposes at 172 °C, melts in a sealed tube at 201-201 °C, reacts in neutral aqueous solution.
Trimethylsulfonium iodide		204	Colorless crystals, decomposes at 203-207 °C. 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
Trimethylsulfonium tetrafluoroborate		163.97	melting point = 205-210 °C
Trimethylsulfonium methylsulfate		188.27	melting point = 92-94 °C 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.
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.