Sulfonyl halide groups occur when a sulfonylfunctional group is singly bonded to a halogenatom. They have the general formula RSO2X 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 and fluorides are of dominant importance in this series.
Sulfonic acid chlorides, or sulfonyl chlorides, are a sulfonyl halide with the general formula RSO2Cl. They are generally colourless compounds that are sensitive to water.
Production
Arylsulfonyl chlorides are made industrially in a two-step, one-pot reaction from the arene and chlorosulfuric acid: 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. Phenyldiazonium chloride reacts with sulfur dioxide and hydrochloric acid to give the sulfonyl chloride: For alkylsulfonyl chlorides, one synthetic procedure is the Reed reaction: Or by treating with SOCl2
Reactions
An obvious reaction is their tendency to hydrolyse to the corresponding sulfonic acid: These compounds react readily with nucleophiles other than water, like alcohols and amines. 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, such as C6H5SO2Na. Chlorosulfonated alkanes are susceptible to crosslinking via reactions with various nucleophiles. Sulfonyl chlorides readily undergo Friedel–Crafts reactions with arenes giving sulfones, for example: The desulfonation of arylsulfonyl chlorides provides a route to aryl chlorides: 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:
Common sulfonyl chlorides
is produced industrially by chlorosulfonation of polyethylene. CSPE is noted for its toughness, hence its use for roofing shingles. An industrially important derivative is benzenesulfonyl chloride. In the laboratory, useful reagents include tosyl chloride, brosyl chloride, nosyl chloride and mesyl chloride.
Sulfonyl fluorides
Sulfonyl fluorides have the general formula RSO2F. "Most, if not all" industrially synthesized perfluorooctanesulfonyl derivatives, such as PFOS, have the sulfonyl fluoride as their precursor. In the laboratory, 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 RSO2Br. In contrast to sulfonyl chlorides, sulfonyl bromides readily undergo light-inducedhomolysis affording sulfonyl radicals, which can add to alkenes, as illustrated by the use of bromomethanesulfonyl bromide, BrCH2SO2Br in Ramberg–Bäcklund reaction syntheses.
Sulfonyl iodides
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. Arenesulfonyl iodides, prepared from reaction of arenesulfinates or arenehydrazides with iodine, can be used as initiators to facilitate the synthesis of polycontaining C–I, C–Br and C–Cl chain ends.
