The general procedure for the synthesis of 5,6-dichloropyridine-3-carboxylic acid from 5,6-dichloronicotinic acid ethyl ester was as follows: in a solvent mixture of tetrahydrofuran (THF), methanol (MeOH) and water (50 mL, 4:1:1, v/v/v), ethyl 5,6-dichloronicotinic acid ethyl ester (1.0 g, 4.5 mmol) and aqueous sodium hydroxide 2N solution (6.75 mL, 13.5 mmol). The reaction mixture was stirred at room temperature for 0.5 hours. Upon completion of the reaction, the mixture was concentrated to remove the organic solvent. Subsequently, the mixture was acidified with 2N hydrochloric acid to a pH of about 2. The acidified mixture was extracted with ether (30 mL x 3). The organic layers were combined, washed with water (50 mL x 3), dried over anhydrous sodium sulfate, and concentrated to give 5,6-dichloropyridine-3-carboxylic acid (800 mg, 91% yield) as a white solid.LCMS (ESI) m/z: 192.0 [M + H]+.
