General procedure for the synthesis of 3,5,6-trichloro-4-hydrazine pyridine-2-carboxylic acid from 3,5,6-trichloro-4-hydrazine pyridine-2-carboxylic acid: to a reaction flask containing 200 mL of boiling water were added 26.1 g (0.1 mol) of 3,5,6-trichloro-4-hydrazine pyridine-2-carboxylic acid, 4.1 g (0.103 mol) of sodium hydroxide pre-dissolved in 25 mL of water and 3.47 g (0.105 mol) of anhydrous hydrazine. The reaction mixture was stirred under reflux conditions for 30 minutes. Subsequently, another 4.1 g (0.103 mol) of sodium hydroxide in 25 mL of water was slowly added over 25 minutes and reflux was continued for 45 minutes. Upon completion of the reaction, the mixture was cooled to room temperature and 25 mL of 5N HCl was added. the precipitated solid 3,5,6-trichloro-4-hydrazinylpyridinecarboxylic acid monohydrate was recovered by filtration in a yield of 22.9 g (83% yield) with a melting point of 166-168 °C. The reaction was carried out in aqueous solution.
22.9 g (78 mmol) of 3,5,6-trichloro-4-hydrazinopyridinecarboxylic acid, 115 mL of 2% sodium hydroxide solution and 150 mL of water were mixed to form a clarified solution. At 30°C, 100mL of 10-13% sodium hypochlorite solution was slowly added. Immediate release of gas was observed and stopped after about 3 minutes. 5 minutes after addition of sodium hypochlorite solution, the reaction mixture was acidified with concentrated hydrochloric acid to pH about 2. The mixture was extracted with 150 mL of dichloromethane and the dichloromethane was removed by distillation to give the crude product of 3,5,6-trichloropyridinecarboxylic acid. The crude product was dissolved in 1N NaOH to form a clarified solution, cooled to 0°C and neutralized with 5N HCl at 0°C with stirring. The solid was filtered and washed with water to give a product of sufficient purity (15.5 g, 88% yield) in 68% total yield with a melting point of 147-151 °C.1H NMR (DMSO-d6, 400 MHz): δ 14.31 (brs, 1H, OH, exchangeable with D2O), 8.60 (s, 1H).
