General procedure for the synthesis of 2-amino-6-bromobenzothiazole from potassium thiocyanate and 4-bromoaniline: a solution of 4-bromoaniline (2 mmol) in acetonitrile (15 mL) was slowly added to a solution of potassium thiocyanate (8 mmol) in acetonitrile (15 mL). Subsequently, nano BF3/SiO2 catalyst (0.06 g, 30 mol% BF3) was added to the reaction system and the mixture was placed in an ice-salt bath and mechanically stirred for 30 min. A solution of bromine (4 mmol, 0.2 mL) in acetonitrile (3 mL) was slowly added through a dropping funnel, and the rate of dropping was controlled to ensure that the reaction temperature did not exceed 0 °C. After the addition of the bromine solution, the reaction was continued to be stirred at room temperature for 4 h, during which the progress of the reaction was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the reaction mixture was poured into water, heated in a 70 °C water bath and then thermally filtered to remove the catalyst. The recovered catalyst was washed with acetone and reused. The filtrate was neutralized with 10% NaOH solution, the precipitate was collected by filtration, dried and recrystallized from ethanol (10 mL) to give the target product 2-amino-6-bromobenzothiazole. The product was characterized by physical and spectroscopic data and confirmed by comparison with known samples.6-Bromo-1,3-benzothiazol-2-amine (2e) was a yellow solid with 93% yield and melting point 202-204 °C (literature value 203 °C).FT-IR (KBr, cm-1 ): 3315, 3012, 2835, 1580, 1476, 1261, 920, 742, 512. 1H NMR (400 MHz, CDCl3, δ ppm): 5.44 (s, 2H, NH2), 7.4-7.5 (d, 2H, Ar-H), 7.71 (s, 1H, Ar-H). 13C NMR (100 MHz, DMSO-d6, δ ppm): 119, 120.9, 125.15, 126.07 , 133.1, 152.15, 167.75.
