GENERAL METHODS: A solution of 2-nitroaniline (2 mmol) in acetonitrile (15 ml) was slowly added to a solution of potassium thiocyanate (8 mmol) in acetonitrile (15 ml). Subsequently, 0.06 g (30 mol%) of BF3/SiO2 nanocatalyst 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 acceleration of the drop was controlled to ensure that the reaction temperature did not exceed 0 °C. After the bromine solution was added, the reaction was continued to be stirred at room temperature for 4 h, during which the progress of the reaction was monitored by TLC. Upon completion of the reaction, the reaction mixture was poured into water, heated in a 70 °C water bath and thermofiltered to remove the catalyst. The catalyst was washed with acetone and recycled for reuse. The filtrate was neutralized with 10% NaOH solution and the precipitated solid was collected by filtration, dried and recrystallized with ethanol (10 ml) to give the target product 2-amino-4-nitrobenzothiazole. The structure of the product was confirmed by physical properties and spectral data (FT-IR, 1H NMR, 13C NMR) and verified by comparison with known standards.
Preparation data for 6-bromo-1,3-benzothiazol-2-amine (2e): yellow solid; 93% yield; 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. 167.75.
