5-Chloro-1-yloxy-pyridine-2-carboxylic acid (CAS: 1415898-80-4, 1.2 g, 7 mmol) was used as a raw material and was slowly added to phosphorus trichloride (POCl3, 10 g) at 0 °C. The reaction mixture was warmed up to 95 °C and maintained at this temperature for 1 hour. After completion of the reaction, the mixture was concentrated to dryness under reduced pressure. The residue was dissolved in water (15 mL) and extracted with ethyl acetate (2 × 15 mL). The organic phases were combined and washed sequentially with water (2 × 30 mL) and saturated saline (30 mL). The organic phase was dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford 5,6-dichloro-2-pyridinecarboxylic acid (1 g, 75% yield) as a yellow solid. The product was confirmed by mass spectrometry (EI), m/e = 191.9 [M + H]+.
