The general procedure for the synthesis of 2-chloro-3-trichloromethylpyridine from 2-hydroxynicotinic acid is as follows: a mixture of 2-hydroxypyridine-3-carboxylic acid (100.0 mmol), phenylphosphonic dichloride (33.0 mmol) and phosphorus pentachloride (330.0 mmol) was slowly heated to 160°C and distilled to remove the by-product phosphorus oxychloride (POCl3). Subsequently, the reaction mixture was stirred continuously at the same temperature for 5 hours. The completion of the reaction was confirmed by thin layer chromatography (TLC) monitoring. At the end of the reaction, the remaining phosphorous trichloride was removed by vacuum evaporation. The residue was carefully poured into ice water and neutralized with saturated aqueous sodium carbonate solution to pH neutral, followed by extraction with ethyl acetate. The organic phase was washed with deionized water, dried over anhydrous sodium sulfate and concentrated under reduced pressure to remove the solvent. The resulting crude product was purified by silica gel column chromatography or purified by distillation.
