The hydrolysis of 4-amino- and 4-dimethylaminobenzene sulfonyl chlorides: an unprecedented case of independence of reactivity from pH

The reactivity-pH profile for the hydrolysis of 4-aminobenzenesulfonyl chloride 1 has a sigmoid shape with a plateau extending from pH 2 to pH 11; reactivity of N,N-dimethyaminobenzenesulfonyl chloride 4 is invariant over an even wider pH range (0 to 14.7). These results, together with the activation data determined at selected pH’s for compound 1, are interpreted in light of the occurrence of a reaction mechanism that is dissociative in nature, in which nucleophilic assistance by solvent molecules is given to the amino group of 1 acting as ‘internal nucleophile’.