Synthesis
The general procedure for the synthesis of 3-fluoro-4-bromobenzoic acid from 3-fluoro-4-bromotoluene was as follows: potassium permanganate (66.0 g, 0.42 mol) was added to a mixed solution of pyridine and water (1:1 ratio, 200 mL) containing 1-bromo-2-fluoro-4-methylbenzene (20.0 g, 0.10 mol) in batches. The reaction mixture was stirred at 90 °C for 3 hours. After completion of the reaction, it was cooled to room temperature and filtered through a diatomaceous earth pad. The diatomaceous earth pad was washed sequentially with 3N sodium hydroxide solution (500 mL) and water (400 mL). Subsequently, ethanol was removed by distillation under reduced pressure and the residue was acidified to pH=2 with 6N hydrochloric acid to produce a white precipitate. The precipitate was filtered and dried to give 4-bromo-3-fluorobenzoic acid as a white solid (17.0 g, 73% yield).
References
[1] Bioorganic and Medicinal Chemistry Letters, 2001, vol. 11, # 10, p. 1257 - 1260
[2] Journal of Medicinal Chemistry, 2003, vol. 46, # 14, p. 2973 - 2984
[3] Patent: WO2011/21209, 2011, A1. Location in patent: Page/Page column 38
[4] Patent: US2012/101099, 2012, A1. Location in patent: Page/Page column 13; 14
[5] Patent: WO2006/64251, 2006, A1. Location in patent: Page/Page column 80
