7-Amino-1,3-naphthalenedisulfonic acid → 6-Amino-1,3-naphthalenedisulfonic acid

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When 2-naphthylamine (BNA) is sulfonated in oleum, the sulfonation products are principally 2-amino-1,5,7-naphthalene trisulfonic acid and 2-amino-6,8-naphthalenedisulfonic acid (Amino G Acid). Hydrolysis of the trisulfonic acid provides Amino J Acid (2-amino-5,7-naphthalenedisulfonic acid). Thus, using this so-called BNA route, it is possible to prepare a fixed ratio of both Amino J Acid and Amino G Acid. However, because of the known carcinogenicity of 2-naphthylamine, this route is not used. Amino J Acid is primarily made by the sulfonation of 2-amino-1-naphthalenesulfonic acid (Tobias Acid) with 30% oleum followed by hydrolysis of the intermediate 1,5,7-trisulfonic acid. Amino G Acid, on the other hand, is made by the sulfonation of beta naphthol with sulfuric acid and then with 20% oleum, in controlled steps from 15°-80°C., followed by amination by the Bucherer Reaction.

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