3-Chlorosulfonylbenzoic acid

In the reaction of benzoic acid with a large excess of chlorosulfonic acid, the dichloride 273 may be an intermediate. 3-Chlorosulfonylbenzoyl chloride 273 was easily prepared by treatment of 3-chlorosulfonylbenzoic acid 271 widi thionyl chloride and was shown to reform the 3-sulfonyl chloride 271 by reaction with either water or chlorosulfonic acid (Scheme 6). Stewart" successMly reacted cinnamic, salicylic and phenylacetic acid with excess chlorosulfonic acid to obtain the corresponding sulfonyl chlorides. Several ortAo-substituted benzoic acids (274 X = Me, OMe, qjj 110,268-271 q 26 gj.267 treated with excess... 

Benzoyl chloride and benzoic anhydride, by heating with excess chlorosulfonic acid followed by addition of the crude reaction mixture to crushed ice, both afforded 3-chlorosulfonylbenzoic acid. These carboxylic acid derivatives (acid chlorides and anhydrides) are easily hydrolysed to the carboxylic acid group in the work-up procedure, so they behave similffl ly to the parent arylcarboxylic acid. On the other hand, arylcarboxylic acid esters may be chlorosulfonated without loss of the ester group thus methyl-1-naphthalenecarboxylate 297 by treatment with excess chlorosulfonic acid gave the corresponding 5-sulfonyl chloride 298 (Equation 92). Similar results were reported in the chlorosulfonation of ethyl chlorophenoxyacetates in which the ester grouping was retained. 

When unamalgamated zinc dust is used, a considerable proportion of yellow insoluble product is often noted at this point. Since the disulfide has been isolated as an intermediate in a similar reduction of m-chlorosulfonylbenzoic acid,4 it is probable that this material is a mixture of disulfides of varying molecular weight. 

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