General procedure for the synthesis of 6-nitro-1,2-benzisothiazolin-3-one 1,1-dioxide from 2-methyl-5-nitrobenzenesulfonamide: A solution of chromium trioxide (20.4 g, 0.204 mol) in water (150 mL) was added drop-wise to concentrated sulfuric acid (190 mL) under ice-bath conditions. Subsequently, 2-methyl-5-nitrobenzenesulfonamide (10 g, 46.3 mmol) was added and the reaction mixture was stirred at room temperature for 24 hours. Upon completion of the reaction, the mixture was filtered and the residue was washed with water and then dissolved in sodium bicarbonate solution and filtered again under vacuum. The filtrate was acidified with concentrated hydrochloric acid to precipitate. The precipitated product was collected by filtration and washed with plenty of cold water. Finally, the product was dried in a vacuum oven at 40°C to give a white powder in 72% yield. The melting point of the product was 205.6-205.8 °C (literature value: 205-207 °C); IR spectra showed characteristic absorption peaks located at 3103, 1720, 1608, 1541, 1354, 1340, 1184, 1128 cm-1 ; 1H NMR (DMSO-d6, 300 MHz) δ/ ppm: 8.02 (1H, d, J = 8.5 Hz), 8.56 (1H, d, J = 8.2 Hz), 8.71 (1H, s), 10.2 (1H, br, NH); 13C NMR (DMSO-d6, 75 MHz) δ/ ppm: 117.2, 126.4, 129.8, 135.2, 143.0, 151.7, 162.2.
