Sulfonyl halide

Sulfonyl halides have tetrahedral sulfur centres attached to two oxygen atoms, an organic radical, and a halide. In a representative example, methanesulfonyl chloride, the S=O, S−C, and S−Cl bond distances are respectively 142.4, 176.3, and 204.6 pm.^[3]

Sulfonic acid chlorides, or sulfonyl chlorides, are a sulfonyl halide with the general formula RSO₂Cl.

Production

Arylsulfonyl chlorides are made industrially in a two-step, one-pot reaction from an arene (in this case, benzene) and chlorosulfuric acid:^[4]

${\displaystyle {\ce {C6H6 + HOSO2Cl -> C6H5SO3H + HCl}}}$

${\displaystyle {\ce {C6H5SO3H + HOSO2Cl -> C6H5SO2Cl + H2SO4}}}$

The intermediate benzenesulfonic acid can be chlorinated with thionyl chloride as well. Benzenesulfonyl chloride, the most important sulfonyl halide, can also be produced by treating sodium benzenesulfonate with phosphorus pentachlorides.^[5]

Benzenediazonium chloride reacts with sulfur dioxide and hydrochloric acid to give the sulfonyl chloride:

${\displaystyle {\ce {[C6H5N2]Cl + SO2 -> C6H5SO2Cl + N2}}}$

For alkylsulfonyl chlorides, one synthetic procedure is the Reed reaction:

${\displaystyle {\ce {RH + SO2 + Cl2 -> RSO2Cl + HCl}}}$

Reactions

Sulfonyl chlorides react with water to give the corresponding sulfonic acid:

RSO₂Cl + H₂O → RSO₃H + HCl

These compounds react readily with many other nucleophiles as well, most notably alcohols and amines (see Hinsberg reaction). If the nucleophile is an alcohol, the product is a sulfonate ester; if it is an amine, the product is a sulfonamide. Using sodium sulfite as the nucleophilic reagent, p-toluenesulfonyl chloride is converted to its sulfinate salt, CH₃C₆H₄SO₂Na.^[6] Chlorosulfonated alkanes are susceptible to crosslinking via reactions with various nucleophiles.^[7]

Sulfonyl chlorides readily undergo Friedel–Crafts reactions with arenes giving sulfones, for example:

RSO₂Cl + C₆H₆ → RSO₂C₆H₅ + HCl

The desulfonation of arylsulfonyl chlorides provides a route to aryl chlorides:

ArSO₂Cl → ArCl + SO₂

1,2,4-Trichlorobenzene is made industrially in this way.

Treatment of alkanesulfonyl chlorides having α-hydrogens with amine bases can give sulfenes, highly unstable species that can be trapped:

RCH₂SO₂Cl → RCH=SO₂ + HCl

Sulfonamides can be prepared by reaction of sulfonyl chlorides with amines:

RSO₂Cl + R'₂NH → RSO₂NR'₂ + HCl

A readily available sulfonyl chloride source is tosyl chloride.^[8]

Reduction with tetrathiotungstate ions (WS2−4) induces dimerization to the disulfide.^[9]

Common sulfonyl chlorides

Chlorosulfonated polyethylene (CSPE) is produced industrially by chlorosulfonation of polyethylene. CSPE is noted for its toughness, hence its use for roofing shingles.^[7]

An industrially important derivative is benzenesulfonyl chloride. In the laboratory, useful reagents include tosyl chloride, brosyl chloride, nosyl chloride and mesyl chloride.

Sulfonyl fluorides have the general formula RSO₂F. They can be produced by treating sulfonic acids with sulfur tetrafluoride:^[10]

SF₄ + RSO₃H → SOF₂ + RSO₂F + HF

Perfluorooctanesulfonyl derivatives, such as PFOS, are produced from their sulfonyl fluoride, which are produced by electrofluorination^[11]

In the molecular biology, sulfonyl fluorides are used to label proteins. They specifically react with serine, threonine, tyrosine, lysine, cysteine, and histidine residues. The fluorides are more resistant than the corresponding chlorides and are therefore better suited to this task.^[12]

Some sulfonyl fluorides can also be used as deoxyfluorinating reagents, such as 2-pyridinesulfonyl fluoride (PyFluor) and N-tosyl-4-chlorobenzenesulfonimidoyl fluoride (SulfoxFluor).^[13][14]

Sulfonyl bromides have the general formula RSO₂Br. In contrast to sulfonyl chlorides, sulfonyl bromides readily undergo light-induced homolysis affording sulfonyl radicals, which can add to alkenes, as illustrated by the use of bromomethanesulfonyl bromide, BrCH₂SO₂Br in Ramberg–Bäcklund reaction syntheses.^[15][16]

Sulfonyl iodides, having the general formula RSO₂I, are quite light-sensitive. Perfluoroalkanesulfonyl iodides, prepared by reaction between silver perfluoroalkanesulfinates and iodine in dichloromethane at −30 °C, react with alkenes to form the normal adducts, RFSO₂CH₂CHIR and the adducts resulting from loss of SO₂, RFCH₂CHIR.^[17] Arenesulfonyl iodides, prepared from reaction of arenesulfinates or arenehydrazides with iodine, can be used as initiators to facilitate the synthesis of poly(methyl methacrylate) containing C–I, C–Br and C–Cl chain ends.^[18]

In the episode "Encyclopedia Galactica" of his TV series Cosmos: A Personal Voyage, Carl Sagan speculates that some intelligent extraterrestrial beings might have a genetic code based on polyaromatic sulfonyl halides instead of DNA.