General procedure for the synthesis of methyl 4-hydrazinylbenzoate hydrochloride from 2-hydrazinylbenzoic acid: 4M dioxane solution of hydrogen chloride (100 mL, 399.60 mmol) was slowly added to a solution of 2-hydrazinylbenzoic acid (15.2 g, 99.90 mmol) in methanol (200 mL). The reaction mixture was stirred at 90 °C for 5 hours. Upon completion of the reaction, it was cooled to 20 °C and the resulting precipitate was collected by filtration, washed with ether (100 mL) and subsequently dried under vacuum to afford the target product methyl 4-hydrazinobenzoate hydrochloride (16.50 g, 82% yield) as a milky white crystalline solid. Mass spectrometry analysis (ESI-) showed m/z (M-H)- = 165; high performance liquid chromatography (HPLC) retention time was 1.12 min. 1H NMR (400.13 MHz, DMSO-d6) δ 3.81 (3H, s, OCH3), 6.99-7.02 (2H, m, Ar-H), 7.86-7.90 (2H, m, Ar- H), 8.98 (1H, s, NH), 10.47 (3H, s, NH3+).
