Synthesis of 5-bromo-6-chloronicotinic acid: 5-bromo-6-hydroxynicotinic acid (10 g, 45 mmol), tetramethylammonium chloride (5.4 g, 49 mmol), and phosphorus triclosan (20 mL) were sequentially added to a reaction flask, and the mixture was heated to reflux and held for 3 hours. Upon completion of the reaction, the reaction mixture was slowly poured into ice water and stirred continuously for 2 hours. The precipitated solid was collected by filtration, dissolved in ethyl acetate (300 mL) and dried by adding anhydrous sodium sulfate. The desiccant was removed by filtration and the filtrate was concentrated under reduced pressure to give 10.5 g (97% yield) of the target product 5-bromo-6-chloronicotinic acid as a pink solid. The product was characterized by 1H NMR (400 MHz, DMSO-d6): δ 8.53 (d, J = 2.02 Hz, 1H), 8.85 (d, J = 2.02 Hz, 1H), 13.57 (s, 1H).
