Under nitrogen protection and room temperature, 3,4-dimethylpyridine (5.0 g, 46.6 mmol) was dissolved in concentrated sulfuric acid (50.0 mL). Subsequently, N-bromosuccinimide (9.31 g, 51.32 mmol) was added in batches. The reaction mixture was heated to 60 °C and stirred for 18 hours. After completion of the reaction, the mixture was cooled to room temperature, slowly poured into ice-cold water and the pH was adjusted to alkaline with 10% sodium hydroxide solution. The aqueous phase was extracted with ethyl acetate (3 x 50 mL). The organic phases were combined, washed with saturated saline, dried over anhydrous sodium sulfate and concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography (100-200 mesh) to afford 3,4-dimethyl-5-bromopyridine (0.8 g, 9.3% yield) using 5% ethyl acetate in hexane solution as eluent. Mass spectrum (ESI) m/z: 186.0 [M(79Br)+H]+, 188.0 [M(81Br)+H]+; nuclear magnetic resonance hydrogen spectrum (1H NMR, CDCl3): δ 2.31 (s, 3H), 2.36 (s, 3H), 8.23 (s, 1H), 8.51 (s, 1H).
