C([NH:4][C:5]1[CH:13]=[C:12]([N:14]([CH3:16])[CH3:15])[C:11]([N+:17]([O-:19])=[O:18])=[CH:10][C:6]=1[C:7]([OH:9])=[O:8])(=O)C.Cl.O.[OH-].[Na+]>C(O)(=O)C>[NH2:4][C:5]1[CH:13]=[C:12]([N:14]([CH3:15])[CH3:16])[C:11]([N+:17]([O-:19])=[O:18])=[CH:10][C:6]=1[C:7]([OH:9])=[O:8]A mixture of 2-acetylamino-4-dimethylamino-5-nitrobenzoic acid (6.5 g), concentrated hydrochloric acid (20 ml), and water (80 ml) is stirred at 100° C. for 30 minutes. After cooling, solid sodium hydroxide (5 g) and then 10% aqueous sodium hydroxide solution are added until the mixture becomes a clear solution. The resulting solution is adjusted to the pH of about 4 with acetic acid. The precipitate is collected and recrystallized from methanol to give the title compound (4.8 g), mp 240°-250° C.
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