[O:1]=[C:2]([C:9]1[CH:14]=[CH:13][CH:12]=[C:11]([C:15]([O:17]C)=[O:16])[N:10]=1)[CH2:3]C(OCC)=O.O.S(Cl)([Cl:23])(=O)=O>C(OCC)(=O)C>[Cl:23][CH2:3][C:2]([C:9]1[CH:14]=[CH:13][CH:12]=[C:11]([C:15]([OH:17])=[O:16])[N:10]=1)=[O:1]41.4 g of ethyl 3-oxo-3-(6-methoxycarbonyl-2-pyridyl)propionate was dissolved in a solution consisting of 42 ml of water and 414 ml of ethyl acetate, and the obtained solution was then cooled to a temperature between 5° C. and 10° C. Thereafter, a solution obtained by dissolving 35.6 g of sulfuryl chloride in 83 ml of ethyl acetate was added dropwise to the above cooled solution over approximately 30 minutes, while stirring. Thereafter, the obtained mixture was stirred at a temperature between 10° C. and 20° C. for 1 hour. Subsequently, the reaction solution was heated up to approximately 90° C., while the solvent was distilled away from the reaction solution. The reaction solution was continuously heated at a temperature between approximately 90° C. and 100° C. for 2 hours while stirring. Thereafter, the obtained mixed suspension (containing crystals) was cooled to approximately 10° C., and it was then stirred for 1 hour, followed by filtration, so as to obtain 27.99 g of 2-(2-chloroacetyl)-6-pyridine carboxylic acid in the form of yellow-brown crystals (melting point: 184° C. to 189° C.; purity: 98% to 99%).
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