Abstract: 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.

Abstract: A process for the production of an aryl thiol, which comprises hydrogenating an aryl sulfochloride in a protic or aprotic solvent in the presence of platinum as catalyst, at a temperature between 100.degree. and 180.degree. C., with hydrogen under a pressure of 2 to 140 bar, in a single reaction step.