THE FIRST ISOLATION AND CHARACTERIZATION OF FREE PHENYLAMIDOSULFURIC ACID AND ITS RING-SUBSTITUTED DERIVATIVES. POSTULATED INTERMEDIATES IN THE SULFONATION OF AROMATIC AMINES

Abstract Thirteen free arylamidosulfuric acids were prepared and charactrized for the first time. These acids could readily been obtained in a pure state simply by adding concentrated hydrochloric acid to a cold aqueous solution of the corresponding ammonium salts. These compounds are non-hygroscopic, crystalline solids and quite stable at room temperature under anhydrous conditions. The spectral data clearly showed that all the arylamidosulfuric acids exist as zwitterions, ArNH2+–SO3−, in the solid state.