1. In a 250 mL single-necked round-bottomed flask equipped with a magnetic stirrer, 3-fluoro-2-nitrotoluene (4.75 g, 30.6 mmol) and trifluoroacetic acid (20 mL) were added.
2. The reaction system was cooled to 0 °C and concentrated sulfuric acid (96%, 10 mL) was added slowly and dropwise over 10 min.
3. N-bromosuccinimide (8.12 g, 45.6 mmol) was added in batches over 15 min, taking care to control the reaction temperature to no more than 30 °C. The reaction mixture was cooled to 0 °C over 10 min.
4. The reaction mixture was stirred at 0 °C for 20 minutes, then brought to room temperature and continued stirring for 3.5 hours.
5. The reaction mixture was slowly poured into an ice/water (1:1, 500 mL) mixture and diluted with 95:5 hexane/dichloromethane (250 mL) to separate the organic and aqueous layers.
6. The aqueous layer was extracted with hexane (100 mL), the organic phases were combined and washed sequentially with water (2 x 100 mL), saturated aqueous sodium bicarbonate solution (100 mL) and brine (100 mL).
7. The organic layer was dried with anhydrous sodium sulfate, filtered to remove the desiccant, and the filtrate was concentrated under reduced pressure.
8. Suspend the crude product in hexane (40 mL), heat until completely dissolved, concentrate to a volume of about 20 mL, and leave to cool to room temperature overnight.
9. The precipitated yellow crystalline solid was collected by filtration and washed with cold hexane (3 x 2 mL) to afford 1-bromo-4-fluoro-2-methyl-3-nitrobenzene (4.29 g, 60% yield).
10. The mother liquor was concentrated to dryness and the residue was dissolved in hot hexane (5 mL), cooled to room temperature and stirred for 2 h. The additional product was obtained by filtration (1.30 g, 18% yield).
