[NH2:1][C:2]1[C:10]([O:11]C)=[CH:9][C:8]([Cl:13])=[CH:7][C:3]=1[C:4]([O-:6])=[O:5].Br.C([O-])([O-])=O.[Na+].[Na+]>C(O)(=O)C>[NH2:1][C:2]1[C:10]([OH:11])=[CH:9][C:8]([Cl:13])=[CH:7][C:3]=1[C:4]([OH:6])=[O:5]A mixture of 2-amino-5-chloro-3-methoxybenzoate (2.76 g, 12.8 mmol), 48% aqueous solution of hydrobromic acid (25 mL) and glacial acetic acid (1 mL) was heated to reflux for 48 h. The reaction mixture was cooled down to room temperature, treated with saturated solution of Na2CO3 to pH˜6, concentrated and purified by column chromatography (silica gel, 90:10 dichloromethane/methanol) to afford 2-amino-5-chloro-3-hydroxybenzoic acid (0.84 g, 35%) as a light brown solid: MS (ESI+) m/z 188 (M+H).
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