[NH:1]([C:5]1[CH:14]=[CH:13][C:12]2[C:7](=[CH:8][CH:9]=[C:10]([S:15]([OH:18])(=[O:17])=[O:16])[CH:11]=2)[CH:6]=1)C(C)=O.OC1C=CC2C(=CC=CC=2)C=1.S(=O)(=O)(O)O.OC1C=CC2C(=CC=CC=2)C=1S(O)(=O)=O>>[NH3:1].[S:15]([O-:18])([OH:17])=[O:16].[NH4+:1].[NH2:1][C:5]1[CH:14]=[CH:13][C:12]2[C:7](=[CH:8][CH:9]=[C:10]([S:15]([OH:18])(=[O:16])=[O:17])[CH:11]=2)[CH:6]=1A single-vessel process for preparing 2-acetaminonaphthalene-6-sulfonic acid of high purity by sulfonating 2-hydroxynaphthalene with concentrated sulfuric acid, converting the 2-hydroxynaphthalenesulfonic acid formed with ammonia in the presence of ammonium hydrogensulfite into 2-amino-naphthalene-6-sulfonic acid (Bucherer reaction) and N-acetylating the latter to give 2-acetaminonaphthalene-6-sulfonic acid, which comprises, after diluting the sulfonating melt with water, substantially removing any impurities still present in the resulting aqueous solution of 2-hydroxynaphthalene-6-sulfonic acid, in particular 2-hydroxynaphthalene, by extraction with toluene or xylene and/or clarification using active carbon.
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