Synthesis
(a) Synthesis of 2-bromo-4-nitrobenzoic acid: 40 mL of water was added to 20 mL of pyridine solution containing 2-bromo-4-nitrotoluene (4.41 g, 20.0 mmol), and the mixture was heated to 70°C. Potassium permanganate (19.0 g, 120 mmol) was added batchwise over a 40-minute period, and the reaction mixture was subsequently refluxed for 8 hours. After completion of the reaction, the resulting suspension was thermally filtered. The filtrate was acidified with 6N hydrochloric acid to pH<2 under ice bath cooling, precipitated as a solid and filtered to give crude 2-bromo-4-nitrobenzoic acid (1.63 g). The filtrates were combined, the pH was adjusted to acidic with 6N hydrochloric acid and extracted with ethyl acetate and chloroform sequentially. The organic phases were combined, dried over anhydrous magnesium sulfate and filtered, and the filtrate was concentrated under reduced pressure to give the second batch of product (1.61 g). The total mass of the two batches of product was 3.24 g and the yield was 66%.
References
[1] Bioorganic and Medicinal Chemistry, 1999, vol. 7, # 12, p. 3011 - 3024
[2] Organic and Biomolecular Chemistry, 2006, vol. 4, # 3, p. 482 - 492
[3] Angewandte Chemie - International Edition, 2008, vol. 47, # 17, p. 3184 - 3187
[4] Chinese Chemical Letters, 2011, vol. 22, # 12, p. 1411 - 1414
[5] European Journal of Medicinal Chemistry, 2014, vol. 81, p. 59 - 75
