[N:1]([O-])=O.[Na+].[NH2:5][C:6]1[CH:14]=[C:13]([Br:15])[C:12]([Cl:16])=[CH:11][C:7]=1[C:8]([OH:10])=[O:9].O.[Sn](Cl)Cl>O.Cl>[ClH:16].[Br:15][C:13]1[C:12]([Cl:16])=[CH:11][C:7]([C:8]([OH:10])=[O:9])=[C:6]([NH:5][NH2:1])[CH:14]=1A solution of sodium nitrite (3.03 g, 43.9 mmol) in water (14.8 mL) was added dropwise to a cooled (−10° C., NaCl-ice bath) suspension of 2-amino-4-bromo-5-chlorobenzoic acid (10.0 g, 39.9 mmol) in 37% aqueous HCl (39.9 mL) and water (13.3 mL), at such rate that the temperature did not exceed 0° C. The resulting suspension was stirred at 0° C. for 15 min, then was treated with a solution of tin(II) chloride hydrate (22.7 g, 120 mmol) in 37% aqueous HCl (17 mL). The resulting mixture was warmed to room temperature and stirred for 60 min. The precipitate was collected by filtration, washed with water and air-dried overnight to give 4-bromo-5-chloro-2-hydrazinylbenzoic acid hydrochloride as an off-white solid (12.86 g, 96% yield). Mass spectrum m/z 365, 267 (M+H)+. 1H NMR (400 MHz, DMSO-d6) δ 9.05 (br. s., 1H), 7.95 (s, 1H), 7.55 (s, 1H).
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