General procedure for the synthesis of 2,4,6-trichloro-3-nitropyridine from 4-amino-2,6-dichloro-3-nitropyridine: (6) 2,6-dichloro-3-nitropyridin-4-amine (2.27 g, 10.9 mmol) was added to 48 mL of concentrated hydrochloric acid and the mixture was cooled to 0-5 °C. Sodium nitrite (2.26 g, 32.7 mmol) was added to the solution in batches with stirring. After the sodium nitrite was added, the reaction mixture was continued to be stirred at 0-5 °C for 1 h, and then raised to 25 °C for 2 h. The reaction mixture was then stirred for 1 h. The reaction was then stirred for 2 h. The reaction mixture was then stirred for 2 h. After completion of the reaction, the reaction solution was adjusted to pH=7 with 40% sodium hydroxide solution and then extracted with ether. The organic phases were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure. The resulting crude product was eluted with petroleum ether to give 2 g of white solid product in 80.7% yield.
