Trimethylsulfonium

Trimethylsulfonium (systematically named trimethylsulfanium) is an organic cation with the chemical formula (CH₃)₃S⁺ (also written as C₃H₉S⁺).

Trimethylsulfonium

Names
IUPAC name Trimethylsulfonium
Systematic IUPAC name Trimethylsulfanium
Other names Trimesium Trimethylsulfur(1+)
Identifiers
CAS Number	676-84-6 Y
3D model (JSmol)	Interactive image
ChemSpider	1115
PubChem CID	1147
UNII	8U5M0SJV65 Y
CompTox Dashboard (EPA)	DTXSID50862857
InChI InChI=1S/C3H9S/c1-4(2)3/h1-3H3/q+1 Key: NRZWQKGABZFFKE-UHFFFAOYSA-N
SMILES C[S+](C)C
Properties
Chemical formula	(CH3)3S+
Molar mass	77.17 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Compounds

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

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[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. Decomposes at 172 °C, melts in a sealed tube at 201-201 °C, reacts in neutral aqueous solution.[clarification needed][4]
Trimethylsulfonium iodide	[(CH3)3S]+I−	204	Colorless crystals, decomposes at 203-207 °C.[4][5] 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,[clarification needed] density = 1.958 g/cm3[6]
Trimethylsulfonium tetrafluoroborate	[(CH3)3S]+[BF4]−	163.97	melting point = 205-210 °C[7]
Trimethylsulfonium methylsulfate	[(CH3)3S]+CH3OSO−3	188.27	melting point = 92-94 °C[8] 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[clarification needed]

Preparation

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)₂S + CH₃I → [(CH₃)₃S]⁺I⁻

Related

An extra oxygen atom can bond to the sulfur atom to yield the trimethylsulfoxonium ion [(CH₃)₃S=O]⁺, where the sulfur atom is tetravalent and tetracoordinated.

Use

Glyphosate herbicide is often supplied as a trimethylsulfonium salt, referred to as trimesium.^[9]

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.^[10]