The reaction of N-hydroxybenzenesulfonamide (1) with aldehydes was studied. In the presence of strong base, hydroxamic acids are formed. In methanol in the absence of base, rapid acid catalysis by 1 takes place, leading to dimethyl acetais. In this manner acetal formation or hydrolysis can be catalyzed by the mild acids 1 or its O-benzyl ether 6. Treatment of 1 or 6 with base does not appear to furnish nitrenes, as indicated by lack of reaction with olefins.