Sulfuric Acid → 4-(Bromomethyl)-1,2-dihydroquinolin-2-one

30 Grams of acetoacetanilide was dissolved in 30 ml of chloroform, then a solution containing 27 g of bromine in 30 ml of chloroform was added dropwise thereto at a room temperature with stirring. After completion of the addition of bromine, the reaction mixture was refluxed for 30 minutes. The reaction mixture was concentrated under a reduced pressure, the residue obtained was added to 70 ml of a concentrated sulfuric acid with stirring. The addition operation was conducted by keeping the inside of the vessel within 70°-75° C., then the whole mixture was poured into ice-water and the crystals precipitated were collected by filtration. Recrystallized from methanol-chloroform to obtain 20 g of 4-bromomethylcarbostyril in the form of colorless needel-like crystals.