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37% hydrochloric acid (45.5 mL) and o-aminophenol (10.91 g, 0.1 mol) were added to a 250 mL two-necked round-bottomed flask, stirred thoroughly and heated to 120 °C. Methyl vinyl ketone (14.32 mL, 0.175 mol) was added slowly and the reaction was kept at reflux for 6 hours. After completion of the reaction, it was cooled to room temperature and the reaction mixture was neutralized with aqueous sodium hydroxide. Subsequently, extraction was performed with dichloromethane (50 mL × 3). The organic phases were combined, dried with anhydrous magnesium sulfate, and concentrated under reduced pressure to remove the solvent. The crude product was purified by silica gel column chromatography using dichloromethane as eluent. Finally, the solvent mixture of dichloromethane and hexane (1:1, v/v) was used to recrystallize to give 4-methyl-8-hydroxyquinoline (4.38 g, 27.5% yield) as a colorless solid. The NMR hydrogen spectrum (400 MHz, (CD3)2CO, Me4Si) data were as follows: δ 8.68 (d, 1H, J = 4.4 Hz), 7.55 (dd, 1H, J1 = 8.4 Hz, J2 = 1.5 Hz), 7.51 (dd, 1H, J1 = 8.4 Hz, J2 = 7.2 Hz), 7.41 (dd, 1H, J1 = 4.4 Hz, J2 = 0.8 Hz), 7.12 (dd, 1H, J1 = 7.2 Hz, J2 = 1.5 Hz), 2.71 (d, 3H, J = 0.8 Hz).