Synthesis
Step A: 2,4-difluorobenzoic acid (9.985 g, 63.2 mmol) was suspended in concentrated sulfuric acid (30 mL) at 0 °C and fuming nitric acid (30 mL) was slowly added dropwise for 30 minutes. The reaction mixture was then warmed to room temperature and stirring was continued for 16 hours. Upon completion of the reaction, the homogeneous reaction mixture was carefully poured into ice water and extracted with ethyl acetate. The organic phases were combined, washed sequentially with water, dried and finally concentrated under reduced pressure to afford 2,4-difluoro-5-nitrobenzoic acid (12.56 g, 98% yield) as a light yellow solid.
References
[1] Patent: US2004/77696, 2004, A1. Location in patent: Page/Page column 9
[2] Patent: WO2009/75960, 2009, A1. Location in patent: Page/Page column 21
[3] Patent: WO2004/13145, 2004, A1. Location in patent: Page 41
[4] Patent: WO2009/58919, 2009, A1. Location in patent: Page/Page column 21-22
[5] Patent: WO2009/58923, 2009, A1. Location in patent: Page/Page column 11
