Under nitrogen protection, 101.5 g (0.50 mol) of o-phthaloyl dichloride was dissolved in 50 mL of chlorobenzene and added dropwise to 200 mL of chlorobenzene solution containing 35.9 g (0.25 mol) of 2-chloro-5-methylpyridinium-N-oxide, with the dropwise addition process being controlled to be completed within 30 minutes. Subsequently, 50.6 g (0.50 mol) of triethylamine was added to the reaction system. The reaction mixture was continued to be heated under reflux conditions for 12 hours. Upon completion of the reaction, the precipitate was separated by filtration and the filter cake was washed with 50 mL of dichloromethane. The filtrates were combined and the solvent was removed by distillation. The residue was subjected to steam distillation, during which the pH was maintained at 6 by successive additions of 45% sodium hydroxide solution. the distillate was collected, extracted three times with 100 mL of dichloromethane, and the organic phases were combined and distilled to remove the solvent. Eventually, the residue was recrystallized from hexane to give 32.2 g (68% yield) of 2,6-dichloro-3-methylpyridine.
