2-Amino-3-nitro-6-chloropyridine (5 g, 28.8 mmol) was used as starting material and suspended in acetic acid (50 mL). To this suspension was added N-chlorosuccinimide (NCS, 4.04 g, 30.2 mmol) and the reaction mixture was stirred at 100 °C for 1 hour. After completion of the reaction, the mixture was cooled to room temperature, NCS (0.385 g, 2.88 mmol) was added again and stirring was continued at 100 °C for 1 hour. At the end of the reaction, the mixture was cooled to room temperature and the solvent was removed by distillation under reduced pressure. The residue was suspended in distilled water (50 mL), stirred and the pH was adjusted to 8 with saturated sodium bicarbonate solution at 0 °C. The solid product was collected by filtration, washed twice with distilled water and subsequently dried under vacuum to afford 5,6-dichloro-3-nitro-2-aminopyridine (5.5 g, 92% yield) as a yellow solid. The product was characterized by 1H-NMR (DMSO-d6): δ 8.33 (brs, 2H), 8.59 (s, 1H).
