Methanesulfonic Acid → 2,5-Diamino-benzenesulfonamide methanesulfonate

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Methanesulfonic acid (465 mL, 7.16 mol) was added slowly to a solution of 2-benzylamino-5-nitro-benzenesulfonamide (2.20 kg, 7.16 mol) and tetrahydrofuran (11.0 L). The resulting solution was added to a mixture of 10% palladium on carbon (220 g of 50% water wet catalyst) and water (1.1 L) in a hydrogenation reactor. The mixture was further diluted with absolute ethanol (21.0 L) and was then hydrogenated with 55 psi hydrogen at 50° C. for 21 h. Additional 10% palladium on carbon (55 g of 50% water wet catalyst) was added, and hydrogenation at 55 psi and 50° C. was continued for 22 h. The resulting suspension was diluted with water (1.1 L) and the suspension was then filtered through a pad of Celite. The filtrate was partially concentrated in vacuo and was then diluted with acetonitrile (15.4 L). The solution was again partially concentrated in vacuo and diluted with acetonitrile (15.4 L). The resulting suspension was partially concentrated in vacuo and was allowed to stir at 23° C. for 2 h. The suspension was filtered and the solid was then washed with acetonitrile (3 L). The solid was further dried in vacuo at 45° C. to afford the desired product, 2,5-diamino-benzenesulfonamide methanesulfonate (1.88 kg, 6.64 mol, 93%), as a purple solid. 1H NMR (400 MHz, DMSO-d6) δ: 2.34 (3H, s), 6.05 (2H, b), 6.87 (1H, d, J=8.6 Hz), 7.20 (1H, dd, J1=8.6 Hz, J2=2.3 Hz), 7.38 (2H, s), 7.53 (1H, d, J=2.3 Hz), 9.62 (3H, b). LC-MS (ESI) calcd for C6H9NO2S 187.04, found 187.9 [M+H+].

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