1. Concentrated nitric acid (10 mL) is slowly added dropwise to a solution of concentrated sulfuric acid (120 mL) containing 3-bromobenzaldehyde (11.7 mL, 100 mmol) at 5°C. The reaction system is allowed to come to room temperature with continuous stirring overnight.
2. The reaction system was allowed to warm naturally to room temperature with continuous stirring overnight.
3. The reaction mixture was slowly poured into ice water and the resulting precipitate was collected by filtration. 4.
4. The precipitate was dissolved in dichloromethane, dried by adding anhydrous magnesium sulfate, and the solvent was subsequently concentrated under reduced pressure.
5. The crude product was purified by fast column chromatography on silica gel with 25% ethyl acetate/isohexane as eluent to afford the target compound 5-bromo-2-nitrobenzaldehyde (16g, 70% yield).
6. The product NMR hydrogen spectral data (500 MHz, CDCl3): δ 10.41 (1H, s), 8.06 (1H, d, J = 2.1 Hz), 8.02 (1H, d, J = 8.6 Hz), 7.87 (1H, dd, J = 2.1,8.6 Hz).
