PROCESS FOR THE PREPARATION OF 2-AMINO-1-NAPHTHALENE SULFONIC ACID

摘要

The invention relates to an improved process for the production of 2-amino-1-naphthalenesulfonic acid (Tobias acid). This improved process makes it possible to obtain Tobias acid which has only a very low content of 2-aminonaphthalene and in high space-time yield. The process starts from 2-hydroxynaphthalene and comprises the following main reaction steps: (a) the sulfonation of 2-hydroxynaphthalene to 2-hydroxynaphthalene-1-sulfonic acid (oxy-Tobias acid) with chlorosulfonic acid, in an inert organic solvent; (b) the neutralization of the liberated hydrochloric acid and excess chlorosulfonic acid still present in the reaction medium and conversion of the 2-hydroxynaphthalene-1-sulfonic acid obtained into the corresponding ammonium salt with ammonia; (c) conversion of the 2-hydroxy group into the 2-amino group by the Bucherer reaction; and (d) the subsequent precipitation of the Tobias acid with dilute sulfuric acid.