(CH3)3S+ in the BPh4- salt (code HEYZAM)

organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, ...

, a sulfonium ion, also known as sulphonium ion or sulfanium ion, is a positively-charged

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

(a " cation") featuring three organic

substituents A substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms ''substituent'' and ''functional group'', as well as ''side ...

attached to sulfur. These organosulfur compounds have the formula . Together with a negatively-charged counterion, they give sulfonium salts. They are typically colorless solids that are

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...

organic solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

Synthesis

Sulfonium compounds are usually synthesized by the reaction of

thioether In organic chemistry, an organic sulfide (British English sulphide) or thioether is an organosulfur functional group with the connectivity as shown on right. Like many other sulfur-containing compounds, volatile sulfides have foul odors. A su ...

s with

alkyl halide The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely us ...

s. For example, the reaction of dimethyl sulfide with

iodomethane Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one ...

yields

trimethylsulfonium iodide Trimethylsulfonium (systematically named trimethylsulfanium and trimethylsulfur(1+)) is an organic cation with the chemical formula (CH3)3S+ (also written as ). Compounds Several salts of trimethylsulfonium are known. X-ray crystallography re ...

: : + → The reaction proceeds by a nucleophilic substitution mechanism (S_N2). Iodide is the leaving group departs. The rate of methylation is faster with more electrophilic methylating agents, such as

methyl trifluoromethanesulfonate Methyl trifluoromethanesulfonate, also commonly called methyl triflate and abbreviated MeOTf, is the organic compound with the formula CF3SO2OCH3. It is a colourless liquid which finds use in organic chemistry as a powerful methylating agent. T ...

Dimethylsulfoniopropionate Structural Formula V1

Inversion

Sulfonium ions with three different substituents are chiral owing to their pyramidal structure. Unlike the isoelectronic oxonium ions (R3O+), chiral sulfonium ions are resolvable into optically stable enantiomers. e(Et)SCH₂CO₂Hsup>+ is the first chiral sulfonium cation to be resolved into enantiomers. The barrier to inversion ranges from 100 to 130 kJ/mol.

Applications and occurrence

Biochemistry

The sulfonium (more specifically methioninium) species ''S''-adenosylmethionine occurs widely in nature, where it is used as a source of the adenosoyl or methyl radicals. These radicals participate in the biosynthesis of many compounds. Other naturally-occurring sulfonium species are ''S''-methylmethionine ( methioninium) and the related

dimethylsulfoniopropionate Dimethylsulfoniopropionate (DMSP), is an organosulfur compound with the formula (CH3)2S+CH2CH2COO−. This zwitterionic metabolite can be found in marine phytoplankton, seaweeds, and some species of terrestrial and aquatic vascular plants ...

(DMSP).

Organic synthesis

Sulfonium salts are precursor to sulfur

ylide An ylide or ylid () is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both atoms ...

s, which are useful in carbon–carbon bond-forming reactions. In a typical application, a R₂S⁺CH₂R′ center is deprotonated to give the ylide R₂S⁺CHR⁻. Tris(dimethylamino)sulfonium difluorotrimethylsilicate (CH₃)₂N)₃Ssup>+ ₂Si(CH₃)₃sup>− is a popular fluoridation agent.{{OrgSynth , author = W. J. Middleton , title = Tris(dimethylamino)sulfonium difluorotrimethylsilicate , volume = 64 , pages = 221 , year = 1986 , doi = 10.15227/orgsyn.064.0221 Some azo dyes are modified with sulfonium groups to give them a positive charge. The compound

triphenylsulfonium triflate Photoacids are molecules which become more acidic upon absorption of light. Either the light causes a photodissociation to produce a strong acid or the light causes photoassociation (such as a ring forming reaction) that leads to an increased ac ...

is a

photoacid Photoacids are molecules which become more acidic upon absorption of light. Either the light causes a photodissociation to produce a strong acid or the light causes photoassociation (such as a ring forming reaction) that leads to an increased ac ...

, a compound that under light converts to an acid.

References

External links

IUPAC definition
(short pdf) Cations Sulfur ions