154093-72-8

112811-72-0

154093-72-8

About 500 mL of DMSO filtrate from the nucleophilic substitution reaction was transferred to a 1000 mL reactor and anhydrous calcium chloride (about 33 g) was added under stirring conditions. The reaction mixture was cooled with stirring to 0-5 °C and maintained in this temperature range for 30 minutes. Subsequently, the pH was adjusted to 4 with a 15% aqueous hydrochloric acid solution, the temperature was maintained between 0-5°C, and stirring was continued for 3 hours. Upon completion of the reaction, the precipitated product was collected by filtration, washed well with acetone and then dried. A dry 1-cyclopropyl-6,7-difluoro-8-hydroxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (about 35 g) with a purity of more than 90% was finally obtained.