Sulfonamides s. Sulfonic acid amides

Cleavage of the S-N bond734 of sulfonamides, yielding sulfonic acids, has preparative interest when purification of the sulfonic acid by way of the chloride is difficult and is better achieved by recrystallization of the amide prepared from the chloride. The amide is hydrolysed in a hydrochloric acid medium.735 HC1... 

Sulfonic acids, R(Ar)S03H, form derivatives similar to those of carboxylic acids (see Table 16-3). These are sulfonyl chlorides, sulfonates (esters), and sulfonamides. The transsulfonylation reactions are similar to the transacylation reactions, except that the ester and amide cannot be made directly from the acid. See Problem 13.17 for preparation of sulfonyl chlorides and esters and Problem 13.18 for use of sulfonate esters as substrates in S l and S,42 reactions. 

Sulfonyl chlorides as well as esters and amides of sulfonic acids can be hydrolyzed to the corresponding acids. Sulfonyl chlorides can by hydrolyzed with water or with an alcohol in the absence of acid or base. Basic catalysis is also used, though of course the salt is the product obtained. Esters are readily hydrolyzed, many with water or dilute alkali. This is the same reaction as 10-4, and usually involves R —O cleavage, except when R is aryl. However, in some cases retention of configuration has been shown at alkyl R, indicating S—O cleavage in these cases. Sulfonamides are generally not hydrolyzed by alkaline treatment, not even with hot concentrated alkali. Acids, however, do hydrolyze sulfonamides, but less readily than they do sulfonyl halides or sulfonic esters. Of course, ammonia or the amine appears as the salt. However, sulfonamides can be hydrolyzed with base if the solvent is HMPA. ... 

Chloro-2-methylbenzene sulfonamide 4-Chloro-2,5-dimethyl-benzene sulfonamide 2-Carboxy-S-methyl benzene sulfonamide (4-Toluic acid-2-sulfon-amide)... 

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