C(N[C:5]1[C:6]([N+:16]([O-:18])=[O:17])=[C:7]([C:11]([Cl:15])=[CH:12][C:13]=1[Cl:14])[C:8]([OH:10])=[O:9])(=O)C.[OH-:19].[K+].Cl>O.C(OCC)(=O)C>[Cl:14][C:13]1[CH:12]=[C:11]([Cl:15])[C:7]([C:8]([OH:10])=[O:9])=[C:6]([N+:16]([O-:18])=[O:17])[C:5]=1[OH:19]3-Acetamido-4,6-dichloro-2-nitrobenzoic acid (1-5) (9.7 g, 0.033 mol) was added to a solution of KOH (18.7 g, 0.034 mol) in H2O (85 mL). The solution was heated under reflux for 18 h and cool to room temperature. Conc HCl was added to adjust the pH to 0. The mixture was diluted with ethyl acetate and H2O and left to stir at room temperature for 30 min. The layers were separated; the aqueous layer was extracted with ethyl acetate (3×), the extracts combined with the original organic layer, washed with brine, dried and concentrated to yield 4,6-dichloro-3-hydroxy-2-nitrobenzoic acid (1-6) as a dark red solid (7.4 g, 89%); m.p. 188-189° C. (lit.4 m.p. 186° C. (dec)).
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