Pyridine → 2-Amino-5-[(methylsulfonyl)amino]benzenesulfonamide

2,5-Diamino-benzenesulfonamide (4.20 kg, 22.4 mol) was dissolved in dichloromethane (120 L) and pyridine (8.00 kg, 89.9 mol), and the resulting solution was cooled to 0° C. Methanesulfonyl chloride (2.80 kg, 24.4 mol) was added slowly, and the resulting mixture was allowed to warm to 23° C. and stirred for 2 days. The mixture was filtered and the resulting solid was washed with dichloromethane (2×20 L). The solid was diluted with water (100 L) and 1.0 M aqueous hydrochloric acid solution (25 L), and was then stirred at 23° C. for 1 h. The mixture was filtered and the resulting solid was washed with water (20 L) and then with methyl-tert-butyl ether (2×10 L). The solid was further dried in vacuo at 45° C. to afford the desired product, 2-amino-5-methanesulfonylamino-benzenesulfonamide (4.39 kg, 16.5 mol, 73%) as a pale pink solid. 1H NMR (400 MHz, CD3OD) δ: 2.89 (3H, s), 6.82 (1H, d, J=8.5 Hz), 7.20 (1H, dd, J1=8.5 Hz, J2=2.5 Hz), 7.58 (1H, d, J=2.5 Hz). LC-MS (ESI) calcd for C7H11N3O4S2 265.02, found 266.0 [M+H+].