[Synthesis]
Under nitrogen protection, 2.44 g (11.9 mmol) of 1-acetyl-4-chloronaphthalene was dissolved in 5 mL of freshly distilled pyridine, to this solution was added 3.33 g (13.1 mmol) of iodine dissolved in 15 mL of freshly distilled pyridine. The mixture was heated to reflux for 40 minutes, cooled to room temperature and diluted with ether until a brown precipitate formed. The precipitate was collected by filtration, suspended in 12 mL of 6 M aqueous sodium hydroxide solution and heated to reflux for 2 hours. After cooling, the solution was acidified with 10% hydrochloric acid and the crude 4-chloro-1-naphthalenecarboxylic acid was extracted into ether and the ether extract was washed with brine. After drying over magnesium sulfate, the solution was concentrated in vacuum. The product was dissolved in 25 ml of methanol and 5 ml of concentrated sulfuric acid was carefully added. The solution was heated to reflux for 3 hours. After cooling to room temperature, the crude ester was extracted into ether, the ether solution was washed with brine and dried (magnesium sulfate). The solution was concentrated in vacuum to give 1.66 g (63% yield) of methyl 4-chloro-1-naphthalenecarboxylate as a brown oil, which could be used without further purification. NMR hydrogen spectrum (300 MHz, deuterated chloroform) δ 3.90 (single peak, 3H), 7.38 (double peak, J = 7.8 Hz, 1H), 7.45-7.56 (multiple peaks, 2H), 7.87 (double peak, J = 8.1 Hz, 1H), 8.18 (double peak, J = 8.4 Hz, 1H), 8.93 (double peak, J = 8.1 Hz, 1H); NMR carbon spectrum (75.5 MHz, deuterated chloroform) δ52.1,124.6,124.9,125.8,126.2,127.1,128.3,129.9,130.7,132.3,137.2,166.9; GC/MS (electron bombardment) m/z (relative intensity) 220 (61), 189 (100) , 161 (48), 126 (42). A mixture of 0.25 g (1.1 mmol) of methyl 4-chloro-1-naphthalenecarboxylate and 2.10 g (37.4 mmol) of potassium hydroxide in 20 mL of water was heated to reflux for 12 h under nitrogen protection. The reaction mixture was cooled to room temperature, acidified with concentrated hydrochloric acid, and the product extracted into ether and dried (magnesium sulfate). The organic phase was concentrated in vacuum to give 0.27 g (88% yield) of 4-chloro-1-naphthalenecarboxylic acid as an off-white solid: melting point 223-224 °C (literature value 220-221 °C); NMR hydrogen spectrum (300 MHz, deuterium dimethylsulfoxide) δ 7.74-7.81 (multiple peaks, 3H), 8.11 (double peaks, J=6 Hz, 1H), 8.28- 8.31 (multiple peaks, 1H), 8.93-8.97 (multiple peaks, 1H), 13.8 (broad peaks, 1H); NMR carbon spectrum (75.5 MHz, deuterium dimethylsulfoxide) δ 124.7,126.1,126.7,127.9,128.3,129.0,130.4,130.6,132.3,135.7, 168.5. |