Sulfonyl halide

Sulfonyl halide groups occur when a sulfonyl functional group is singly bonded to a halogen atom. They have the general formula R-SO₂-X where X is a halogen. The stability of sulfonyl halides decreases in the order fluorides>chlorides>bromides>iodides, all four types being well known. The sulfonyl chlorides are of dominant importance in this series.

Structure

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 1.424, 1.763, and 2.046 Å.

Sulfonyl chlorides

File:Sulfonyl chloride.png

General structure of a sulfonic acid chloride

Sulfonic acid chlorides, or sulfonyl chlorides, are a sulfonyl halide with the general formula R-SO₂Cl. They are generally colourless compounds that are sensitive to water.

Production

Arylsulfonyl chlorides are prepared industrially in a two-step, one-pot reaction from the arene and chlorosulfuric acid:

C₆H₆ + HOSO₂Cl → C₆H₅SO₃H + HCl

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(V) chlorides.

Phenyldiazonium chloride reacts with sulfur dioxide and HCl to give the sulfonyl chloride:

[C₆H₅N₂]Cl + SO₂ → C₆H₅SO₂Cl + N₂

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

RH + SO₂ + Cl₂ → RSO₂Cl + HCl

Reactions

The most obvious reaction is their tendency to hydrolyse to the corresponding sulfonic acid:

C₆H₅SO₂Cl + H₂O → C₆H₅SO₃H + HCl

These compounds react readily with nucleophiles other than water, like 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, sulfonyl chlorides convert to the sulfinate salts, e.g., C₆H₅SO₂Na.

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

RSO₂Cl + C₆H₆ → RSO₂C₆H₅ + HCl

The desulfonation of arylsulfonyl chlorides provides a way to make aryl chlorides:

ArSO₂Cl → ArCl + SO₂

1,2,4-Trichlorobenzene is prepared 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

The only industrially important sulfonyl chloride is the benzene derivative. In the laboratory, useful reagents include tosyl chloride, brosyl chloride, nosyl chloride and mesyl chloride.

Sulfonyl fluorides

Sulfonyl fluorides have the general formula R-SO₂-F and can be important sulfonyl halide synthetic precursors. For example, "most, if not all" industrially synthesized perfluorooctanesulfonyl derivatives, such as PFOS, have the sulfonyl fluoride as their precursor. Sulfonyl fluorides are used in molecular biology as reactive probes. They specifically react with residues based on serine, threonine, tyrosine, lysine, cysteine and histidine. The fluorides are more resistant than the corresponding chlorides and are therefore better suited to this task

Sulfonyl bromides

Sulfonyl bromides have the general formula R-SO₂-Br. In contrast to sulfonyl chlorides, sulfonyl bromides readily undergo light-induced homolysis affording sulfonyl radicals, which can add to olefins, as illustrated by the use of bromomethanesulfonyl bromide, BrCH₂SO₂Br in Ramberg-Bäcklund reaction syntheses.

Sulfonyl iodides

Sulfonyl iodides, having the general formula R-SO₂-I, are quite light-sensitive. Perfluoroalkanesulfonyl iodides, prepared by reaction between silver perfluoroalkanesulfinates and iodine in dichloromethane at −30 °C, react with olefins to form the normal adducts, RFSO₂CH₂CHIR and the adducts resulting from loss of SO₂, RFCH₂CHIR. 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.

In popular culture

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.