Step 2. 4-(Methylamino)-3-nitrobenzoic acid (9.8 g, 49.96 mmol) and palladium-carbon catalyst (1 g) were suspended in methanol (200 ml), and the reaction was stirred for 2 hours at room temperature and under hydrogen atmosphere. Upon completion of the reaction, the solid catalyst was removed by filtration. The filtrate was concentrated under reduced pressure to afford 3-amino-4-(methylamino)benzoic acid (8.2 g, 99% yield) as a white solid. The product was confirmed by LC-MS (electrospray ionization, m/z): [M + H]+ 167.11. 1H-NMR (300 MHz, DMSO-d6) δ 7.47-7.51 (m, 1H), 7.37 (d, J = 2.1Hz, 1H), 6.53 (d, J = 8.4Hz, 1H), 2.90 (s, 3H).
