Hydrochloric Acid → 4-Bromo-1-chloro-2-fluorobenzene

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Reaction Steps

2-Chloro-5-bromoaniline (258 g) is added to concentrated hydrochloric acid (750 ml) and the mixture is stirred at 80°-90° C. until formation of a homogeneous suspension. Then, it is cooled and diazotized at 0°-5° C. by dropwise addition of sodium nitrite (95.1 g) in water (330 ml) during 1 hour. The mixture is stirred for an additional 20 minutes and then a solution of fluoroboric acid (700 ml) (prepared by dissolving 264 g of boric acid in 744 ml of 40% hydrofluoric acid) is added. After 30 minutes of stirring, the separated fluoroborate was filtered, washed successively with a small amount of a fluoroboric acid solution, ethanol and ether, and dried thoroughly in air and in vacuo. The thermal decomposition of the fluoroborate is carried out in two portions. Each portion is heated in a flask with a direct flame, the internal temperature during the decomposition being 130°-170° C. The distillates are combined and shaken with water (250 ml) and ether (250 ml). The ethereal layer is washed with 10% sodium hydroxide solution, 3 N-HCl and water and dried over sodium sulfate. The ether is evaporated and the residue is distilled, yielding 184.2 g (70%) of 2-chloro-5-bromofluorobenzene, b.p. 130°-142° C./20 Torr.

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