The general procedure for the synthesis of 5,5'-dibromo-2,2'-bipyridine from 2,2'-bipyridine was as follows: firstly, 2,2'-bipyridine (4.99 g, 0.032 mol) was placed in a hydrothermal reactor with bromine (10.24 g, 0.064 mol), and the reaction was heated up to 150 °C for 15 hours. Upon completion of the reaction, the mixture was cooled to room temperature and the resulting solid product was pulverized and washed with Na2SO3 solution to remove unreacted bromine. Subsequently, the reaction mixture was alkalized with sodium hydroxide solution and the solid product was collected by filtration. Purification by silica gel column chromatography (eluent: CH2Cl2) afforded 5,5'-dibromo-2,2'-bipyridine as a white solid (8.64 g, 86% yield). The melting point of the product was 221.6-222.1°C. 1H-NMR (400 MHz, CDCl3, δ): 7.95 (d, 2H), 8.28 (s, 2H), 8.71 (d, 2H); 13C-NMR (100 MHz, CDCl3, δ): 121.47 (C5), 122.25 (C3), 139.64 (C4 ), 150.28 (C6), 153.64 (C2); IR (KBr, cm-1): 3049 (C-H stretching vibration), 1562, 1453, 1356 (aromatic ring stretching vibration), 636 (C-Br stretching vibration). Elemental analysis (C10H6N2Br2) calculated values: C 38.22%, H 1.91%, N 8.92%, Br 50.95%; measured values: C 38.26%, H 1.94%, N 8.90%, Br 50.97%.
