General procedure for the synthesis of 6-nitro-2-(3H)-benzothiazolone from 2-hydroxybenzothiazole: 3H-benzothiazol-2-one (10 g, 66 mmol) was added to 70% nitric acid (20 mL), and the reaction was stirred for 3 h at 20 °C. After completion of the reaction, the precipitate was collected by filtration and washed with deionized water. The crude product was purified by recrystallization from anhydrous ethanol. The yield of this synthesis step was 90% and the melting point of the product was 228-229 °C. It was characterized by 1H NMR (300 MHz, DMSO-d6): δ 7.28 (d, J = 8.9 Hz, 1H, H4), 8.18 (dd, J = 8.9 Hz, J = 2.4 Hz, 1H, H5), 8.65 (d, J = 2.5 Hz, 1H, H7), and 12.54 (br s, 1H, NH).13C NMR ( 75 MHz, DMSO-d6) characterization: δ 111.9 (CH), 119.6 (CH), 123.2 (CH), 125.0 (Caro), 142.5 (Caro), 142.9 (Caro), 171.0 (CO).LCMS (ESI-) analysis: calculated value of [M-H+] is 195.0; measured value is 195.0.
