6-Chloro-2-picolinic acid methyl ester is prepared by the reaction of methanol and 6-Chloropicolinic acid. The specific synthesis steps are as follows:
Add thionyl chloride (3.7 ml, 50.8 mmol) to a solution of 6-chloropicolinic acid (4.0 g, 25.4 mmol) in methanol (85 ml) at 0 C. Stir the resultant solution for 15 minutes at 0 C, 0.5 hours at room temperature, and 6 hours at 50 C. Concentrate the reaction in vacuo and dilute with CHCl3 (150ml). Wash the organic solution with saturated aqueous sodium bicarbonate (3 x 100 ml), and brine (1 x 100 ml) and dry with sodium sulfate. Filtration and concentration afford methyl 6-chloropicolinate 4.38 g (100 percent) as a white solid. 1H NMR (CDCl3): δ 8.05 (m, 1H), 7.73 (m, 1H), 7.42 (m, 1H), 3.95 (s, 3H).
