Synthesis
General procedure for the synthesis of 2-bromo-5-chloroaniline from 2-bromo-5-chloronitrobenzene: 1-bromo-4-chloro-2-nitrobenzene (140 g, 0.59 mol) was dissolved in 2.5 L of methanol and heated gently in a hot water bath at 50 °C. A solution of ammonium formate (303 g, 4.81 mol) in 500 mL of water was added slowly. Zinc powder (155 g, 2.36 mol) was carefully added in batches, taking care to control the exothermic and reflux rate of the reaction. The addition of zinc powder needs to be done carefully to avoid excess unreacted zinc residue. After completion of the reaction, it was cooled to room temperature and filtered through a pad of diatomaceous earth (Celite). The filtrate was concentrated under reduced pressure until a two-phase mixture of red oil and water appeared. The product was extracted with diethyl ether (5 × 200 mL). The organic phases were combined, dried with anhydrous sodium sulfate, decanted and concentrated under reduced pressure to give a reddish brown oil. The oil was redissolved in 150 mL of mixed dichloromethane/hexane solvent and filtered through a short column of silica gel. The filtrate was concentrated under reduced pressure to give an orange colored oil. Hexane (200 mL) was added and cooled in a dry ice bath to precipitate 2-bromo-5-chloroaniline as a light yellow solid (92.1 g, 75% yield), which was collected by vacuum filtration.
References
[1] Patent: US2005/192310, 2005, A1. Location in patent: Page/Page column 22-23
[2] Patent: US2017/158704, 2017, A1. Location in patent: Paragraph 0678; 0679
[3] Farmaco, 2003, vol. 58, # 9, p. 723 - 738
[4] European Journal of Organic Chemistry, 2018, vol. 2018, # 26, p. 3416 - 3425
[5] Angewandte Chemie - International Edition, 2008, vol. 47, # 5, p. 888 - 890
