Sodium Hydroxide → 5-Chlorofuran-2-carboxylic acid

5-Chloro-2-furancarboxylic acid ethyl ester (8 g) (synthesized in accordance with the method described in Chem. Pharm. Bull., 40, 1966 (1992)) was dissolved in ethanol (50 ml), and 1N aqueous sodium hydroxide (50 ml) was added. The mixture was stirred at room temperature for 1 hour and concentrated under reduced pressure. The residue was dissolved in water and washed with diethyl ether. The aqueous layer was acidified with 1N hydrochloric acid and extracted with ethyl acetate. The extract was washed with water and saturated aqueous sodium chloride, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. Precipitated crystals were collected by filtration and washed with diethyl etherhexane to give 5-chloro-2-furancarboxylic acid (5.3 g) as crystals.