Ethyl 4-aminobenzoate (4.9 g, 30.0 mmol) was dissolved with potassium thiocyanate (11.6 g, 120.0 mmol) in acetic acid (180 mL), followed by the slow dropwise addition of acetic acid solution (20 mL) containing bromine (1.5 mL, 30.0 mmol). The reaction was carried out at 19 °C and the titration process was controlled to be completed within 20 min. After the dropwise addition, the reaction system was gradually warmed up to room temperature and the reaction was continued with stirring overnight. Upon completion of the reaction, the reaction solution was slowly poured into water (100 mL) and stirred for 10 minutes. Subsequently, ammonium hydroxide solution was added dropwise to the mixture and the pH was adjusted to about 8. The reaction mixture was filtered and the resulting filter cake was washed sequentially with water. Finally, the product was dried under vacuum to give 6.7 g of yellow solid, ethyl 2-aminobenzo[d]thiazole-6-carboxylate in 100% yield. The structure of the product was confirmed by 1H NMR (400 MHz, DMSO): δ 8.28 (d, J = 1.6 Hz, 1H), 7.88 (s, 2H), 7.82 (dd, J = 1.6 Hz, 8.4 Hz, 1H), 7.37 (d, J = 8.4 Hz, 1H), 4.29 (q, J = 7.2 Hz, 2H), 1.32 (t, J = 7.2 Hz, 3H).
