[OH:1][C:2]1[C:10]([N+:11]([O-:13])=[O:12])=[CH:9][C:5]([C:6]([OH:8])=[O:7])=[CH:4][C:3]=1[O:14]C>Br>[OH:14][C:3]1[CH:4]=[C:5]([CH:9]=[C:10]([N+:11]([O-:13])=[O:12])[C:2]=1[OH:1])[C:6]([OH:8])=[O:7]A solution of 2.6 g of 4-hydroxy-3-methoxy-5-nitrobenzoic acid in 26 ml of constant-boiling hydrobromic acid is heated under reflux for 2 hours. After cooling the solvent is distilled in a water-jet vacuum. The crystalline residue is recrystallized from 50 ml of water at boiling temperature. There is obtained 3,4-dihydroxy-5-nitrobenzoic acid in the form of yellow crystals of m.p. 224°-226°.
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