The general procedure for the synthesis of 4-ethyl-1-naphthalenecarboxylic acid (15) from the compound (CAS: 824430-38-8) was as follows: a mixture of 3.70 g (10.5 mmol) of the above mentioned diphenyl amide, 23.2 g of potassium hydroxide (KOH), and 154 mL of diethylene glycol was heated and refluxed for 8 hours. After completion of the reaction, the reaction mixture was cooled, diluted with 1.13 L of water and the precipitated solid was filtered. The filtrate was acidified with concentrated hydrochloric acid until the precipitation was complete. The solid was collected and dried to give 1.90 g (90% yield) of the target product 4-ethyl-1-naphthalene carboxylic acid (15) with a melting point of 125-127 °C (literature value 129-130 °C). The structure of the product was confirmed by nuclear magnetic resonance hydrogen spectroscopy (1H NMR, 300 MHz, CDCl3) and carbon spectroscopy (13C NMR, 75.5 MHz, CDCl3) with the following data: 1H NMR δ 1.44 (t, J = 7.3 Hz, 3H), 3.20 (q, J = 7.5 Hz, 2H), 7.44 (d, J = 7.6 Hz, 1H) , 7.59-7.70 (m, 2H), 8.16 (d, J = 8.2 Hz, 1H), 8.39 (d, J = 7.4 Hz, 1H), 9.21 (d, J = 8.6 Hz, 1H); 13C NMR δ 14.7, 26.5, 123.8, 124.1, 125.0, 126.1, 126.6, 127.5, 131.9, 132.1, 147.5, 173.7.
