General procedure for the synthesis of methyl 2,5-dichloronicotinate from methanol and 2,5-dichloronicotinic acid: 2,5-dichloronicotinic acid (20.2 g, 0.105 mol) was dissolved in methanol (500 mL) at 0 °C and pure thionyl chloride (38 mL, 63 g, 0.525 mol) was added slowly. The reaction mixture was stirred at 0 °C for 1 h. After removing the cooling bath, the reaction temperature was allowed to rise naturally to room temperature and stirring was continued for 2 days. After completion of the reaction, the solvent was removed under reduced pressure to give an off-white residue. The residue was dissolved in ether (about 500 mL) and washed sequentially with saturated aqueous NaHCO3 solution (about 300 mL), water (about 300 mL) and brine (about 300 mL). The organic layer was separated, dried with anhydrous MgSO4 and filtered. The solvent was removed under reduced pressure to give methyl 2,5-dichloronicotinate as a white solid (21.0 g, 97% yield).
Methyl 2,5-dichloronicotinate (4.5 g, 22 mmol) was dissolved in an ammonia solution (250 mL, 0.5 M, 0.125 mol) in 1,4-dioxane, sealed in a pressure vessel, and heated at (85±5) °C for 9 days. After completion of the reaction, it was cooled to room temperature, the reaction mixtures were combined and concentrated under reduced pressure to give a white solid. The solid was dissolved in acetone-MeOH (1:1, about 500 mL), adsorbed on silica gel (25 g), and purified by fast column chromatography (hexane-CH2Cl2-Et2O, 25:10:1) to afford methyl 2-amino-5-chloronicotinate (6.08 g, 75% yield).
A solution of LiOH-H2O (1.38 g, 33 mmol) in water (33 mL) was added at once to a suspension of methyl 2-amino-5-chloronicotinate (6.08 g, 27 mmol) in MeOH (110 mL) and stirred at 70 °C for 24 hours. The reaction mixture gradually became homogeneous. The solvent was removed under reduced pressure and the resulting white solid was dried under vacuum (<1 mmHg) to constant weight to give lithium 2-amino-5-chloronicotinate (5.51 g, 95% yield).
