GENERAL METHOD: A solution of 3-methylaniline (2 mmol) in acetonitrile (15 ml) was added to a solution of potassium thiocyanate (8 mmol) in acetonitrile (15 ml). Subsequently, 0.06 g (30 mol% BF3) of BF3/SiO2 nanoparticles was added to the mixture and the mixture was placed in an ice salt bath and mechanically stirred for 30 min. Then, a solution of bromine (4 mmol, 0.2 ml) in acetonitrile (3 ml) was slowly added through a dropping funnel, controlling the rate of addition to ensure that the reaction temperature did not exceed 0 °C. After complete addition of bromine, the reaction mixture 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 mixture was poured into water and heated to 70 °C on a steam bath followed by thermal filtration to remove the catalyst. The catalyst was washed with acetone and recycled for reuse. The filtrate was neutralized with 10% NaOH solution and the precipitate was collected, dried and recrystallized from ethanol (10 ml) to give 2-amino-5-methylbenzothiazole. The product was characterized by physical properties and spectral data (including melting point, FT-IR, 1H NMR and 13C NMR) and confirmed by comparison with known standards.
Spectral data of the selected products: 6-bromo-1,3-benzothiazol-2-amine (2e) as a yellow solid; yield = 93%; melting point = 202-204 °C (literature value 203 °C); FT-IR (KBr) ν/cm-1: 3315, 3012, 2835, 1580, 1476, 1261, 920, 742, 512; 1H NMR ( 400MHz, CDCl3) δ ppm: 5.44 (s, 2H, NH2), 7.4-7.5 (d, 2H, Ar-H), 7.71 (s, 1H, Ar-H); 13C NMR (100MHz, DMSO-d6) δ ppm: 119, 120.9, 125.15, 126.07, 133.1, 152.15, 167.75. 152.15, 167.75.
