[Cl:1][C:2]1[C:10]([N+:11]([O-:13])=[O:12])=[CH:9][CH:8]=[CH:7][C:3]=1C(O)=O.[Br:14]Br.C(=O)(O)[O-].[Na+]>[Hg]=O.C(Cl)(Cl)(Cl)Cl>[Br:14][C:3]1[C:2]([Cl:1])=[C:10]([N+:11]([O-:13])=[O:12])[CH:9]=[CH:8][CH:7]=1A mixture of 2-chloro-3-nitrobenzoic acid (15 g, 74.4 mmol), red mercury oxide (24.2 g, 112 mmol), and carbon tetrachloride (350 mL) were irradiated with a 100 W light bulb and heated at reflux. Bromine (5.75 mL, 112 mmol) was added dropwise over 30 minutes. This was stirred at reflux for 3.5 hours. After cooling to room temperature, aqueous saturated sodium bicarbonate (250 mL) was added and stirred vigorously for 20 minutes. The mixture was filtered and the solids were washed with excess chloroform. This two-phase solution was separated and the aqueous layer back extracted with chloroform (2×200 mL). The organic layers were collected and washed with brine (150 mL), water (150 mL) and dried (magnesium sulfate) and concentrated to give 3-bromo-2-chloronitrobenzene (10.6 g, 60.4%). 1H NMR (CDCl3, 300 MHz): δ7.86 (dd, 1H, J=8.1, 1.5), 7.73 (dd, 1H, J=8.1, 1.5 Hz), 7.31 (t, 1H, J=8.1 Hz) ppm.
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