Acetyl chloride → 4-Chloro-2-methyl-1-oxo-1lambda~5~-pyridine

4-nitro-2-picoline N-oxide (20 g, 130 mmol) was added to acetyl chloride (120 ml, 1688 mmol) in a nitrogen atmosphere at −25° C. The mixture was stirred at −30 to 5° C. for 4 hours and 15 minutes. After the reaction mixture was diluted with ethyl acetate (about 150 ml) and chloroform (about 100 ml), the mixture was concentrated. The residue was purified by silica gel column chromatography (NH silica gel: 200 g, elution solvent: heptane, heptane/ethyl acetate=75/25, 50/50, 25/75, ethyl acetate, ethyl acetate/methanol=20/1) to obtain the title compound (3.14 g) as brown oil. Simultaneously, a crude product (about 17 g) was obtained. The crude product thus obtained was further purified by silica gel column chromatography (NH silica gel: 300 g, elution solvent: heptane, heptane/ethyl acetate=75/25, 40/60, 25/75, ethyl acetate) to obtain the title compound (5.39 g) separately as brown oil.