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.
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.
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.
Arylsulfonyl chlorides are prepared 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(V) chlorides.
Phenyldiazonium chloride reacts with sulfur dioxide and HCl to give the sulfonyl chloride:
For alkylsulfonyl chlorides, one synthetic procedure is the Reed reaction:
The most 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 (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.
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