A Further Investigation of the Symmetrical Chloride of Paranitroorthosulphobenzoic Acid

The sulphobenzoic acids have been the subject of investigation in this laboratory for a number of years past. Among the many interesting facts that have been brought to light in the course of this study, perhaps no others have been attended with more interest than the discovery of well characterized isomerism in the case of the chlorides of orthosulphobenzoic acid, and its paranitro derivative; together with the preparation of a series of isomeric derivatives of these substances. The chlorides themselves have been isolated in the crystalline condition, and have been found to differ markedly, not only in chemical, but in physical properties as well.

The first evidence that such isomerism existed, was obtained by Remsen and Coates who, in the course of an investigation of the action of aniline upon the chloride of orthosulphobenzoic acid, obtained two isomeric anilids quite different in properties, which they designated as fusible and infusible respectively. The following year, Remsen and Kohler obtained one of the chlorides in crystalline form, together with an oil which they did not succeed in crystallizing.

This however was accomplished the succeeding year by Remsen and Saunders, and a still more satisfactory result was obtained by Remsen and McKee in 1895. The chloride melting at 79° was found to yield only the fusible anilid, together with an anil, while from the lower melting chloride, in addition to these, the infusible anilid was also formed.

In 1895, Gray isolated the two corresponding isomeric chlorides of paranitroorthosulphobenzoic acid, the lower melting chloride being obtained in small quantity only. The succeeding year Hollis made a more careful study of this lower melting chloride, and prepared it in considerable quantity.

From evidence drawn from the action of ammonia upon these chlorides, taken in connection with a number of other facts, the higher melting chloride is identified as the one possessing a symmetrical structure, while the lower melting chloride possesses an unsymmetrical structure.