To a solution of acetic acid (160 mL) containing 3,4-dichloroaniline (10 g, 62 mmol) and potassium thiocyanate (48 g, 0.49 mol), a solution of acetic acid (160 mL) with liquid bromine (31 g, 0.19 mol) was slowly added at 0 °C, while stirring was maintained. The reaction temperature was maintained at 0 °C throughout the addition. After addition, the reaction mixture was continued to be stirred at 0 °C for 2 h, and then warmed up to 15 °C for 14 h. The reaction temperature was kept constant at 0 °C for 2 h. The reaction temperature was kept constant at 15 °C for 2 h. Upon completion of the reaction, the reaction solution was diluted with water (100 mL), the pH was adjusted to 7-8 with ammonium hydroxide, and then extracted with ethyl acetate (3 x 50 mL). The organic layers were combined, washed with brine (3 x 300 mL) and subsequently concentrated under reduced pressure. The crude product was purified by preparative HPLC [Apparatus: GX-B; Column: GEMINI 250 × 50 mm, particle size: 10 μm; Mobile phase: 25-50% acetonitrile in water (containing 0.1% TFA, v/v)] to afford the target compound 5,6-dichlorobenzo[d]thiazol-2-amine (2.6 g, 19% yield) as a white solid.LCMS ( ESI): tR = 0.694min, m/z (M+H)+ 219.0. 1H-NMR (CD3OD, 400MHz): δ 7.89 (s, 1H), 7.55 (s, 1H).
