[Synthesis]
4-Hydroxy-8-methylquinolin-2(1H)-one (II) was synthesized from N,N'-bis(2-methylphenyl)malonamide (I) (0.56 g, 2.0 mmol) by the method described in the literature [14]. The procedure was as follows: compound I was dissolved in 3.5 mL of methanesulfonic acid containing 10% phosphorus pentoxide and the reaction was heated at 150 °C for 90 min. Upon completion of the reaction, the dark-colored viscous solution was allowed to cool to room temperature. Water was added to the reaction mixture and the gel gradually solidified after a long standing period. The solid product was collected by filtration and dissolved in 100 mL of 10% sodium hydroxide solution. The sodium hydroxide solution was filtered to remove insoluble impurities, followed by slow acidification with 10% hydrochloric acid to pH 4. The precipitated crude product was collected, washed with water and dried to afford 8-methyl-4-hydroxyquinolin-2(1H)-one (II) as milky-white crystals (0.30 g, 87% yield) with a melting point of 357-358 °C (literature value 360 °C [13]). The product was characterized by FT-IR (KBr, cm^-1): v 3470 (OH), 3100 (NH), 1660 (C=O); 1H NMR (500 MHz, DMSO-d6): δ 11.25 (OH), 10.27 (NH), 7.62 (d, 1H, J=7.8 Hz), 7.30 (d, 1H, J=7.2 Hz ), 7.01 (dd, 1H, J=7.8,7.1 Hz), 5.27 (s, 1H), 2.35 (s, 3H); 13C NMR (125 MHz, DMSO-d6): δ 160.75 (C=O), 158.24 (C-OH), 139.14 (C), 134.10 (C-CH3), 130.78 (CH ), 126.20 (C-H), 124.90 (CH), 116.17 (C), 99.10 (CH), 17.01 (CH3). Elemental analysis (C10H9NO2) calculated values: C, 68.56; H, 5.18; N, 8.00; measured values: C, 68.54; H, 5.12; N, 7.78. |