[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([Cl:8])=[CH:4][C:3]=1[C:9](=[O:11])[CH3:10].[BrH:12].BrBr.C(=O)([O-])[O-].[Na+].[Na+].S([O-])([O-])(=O)=S.[Na+].[Na+]>C(O)(=O)C>[Br:12][CH2:10][C:9]([C:3]1[CH:4]=[C:5]([Cl:8])[CH:6]=[CH:7][C:2]=1[Cl:1])=[O:11]
To an ice-cooled solution of 2′,5′-dichloroacetophenone (1.0 g, 5.0 mmol) in acetic acid (10 mL) was added HBr (˜1%) followed by a solution of bromine (0.80 g, 5.0 mmol) in acetic acid (3 mL). The resultant mixture was warmed to room temperature and stirred overnight. The mixture was poured into ice water and then neutralized with saturated aqueous sodium carbonate solution. Saturated aqueous sodium thiosulfate solution was then added to the mixture. The resultant mixture was extracted with ethyl acetate. The organic phase was washed with saturated aqueous sodium chloride solution, dried over anhydrous sodium sulfate, filtered, and concentrated. Purification by flash column chromatography afforded 2-bromo-1-(2,5-dichlorophenyl)ethanone as an oil (0.70 g, 50% yield). 1H NMR (400 MHz, CDCl3): 7.54 (d, J=2.4 Hz, 1H), 7.43 (m, 1H), 7.40 (m, 1H), 4.68 (s, 2H).
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