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0 °C

A solution of 2,5-dichloronicotinic acid (20.2 g, 0.105 mol, Aldrich) in methanol (500 mL) was cooled to 0° C. and neat thionyl chloride (38 mL, 63 g, 0.525 mol) was added over ˜30 min. The reaction mixture was stirred at 0° C. for 1 hour. The cooling bath was removed, the reaction temperature was allowed to warm to room temperature, and the reaction was allowed to stir for an additional 2 days at room temperature. The solvent was removed under reduced pressure to give an off-white residue. The residue was dissolved in ether (˜500 mL) and the resulting solution was washed successively with saturated aqueous sodium bicarbonate solution (˜300 mL), water (˜300 mL), and brine (˜300 mL). The organic layer was separated, dried over anhydrous magnesium sulfate, and filtered. Removal of the solvent under reduced pressure yielded methyl 2,5-dichloronicotinate (21.0 g, 97% yield) as a white solid.

1. customThe cooling bath was removed
2. temperatureto warm to room temperature
3. stirringto stir for an additional 2 days at room temperature
4. customThe solvent was removed under reduced pressure
5. customto give an off-white residue
6. washthe resulting solution was washed successively with saturated aqueous sodium bicarbonate solution (˜300 mL), water (˜300 mL), and brine (˜300 mL)
7. customThe organic layer was separated
8. dry with materialdried over anhydrous magnesium sulfate
9. filtrationfiltered
10. customRemoval of the solvent under reduced pressure