Thiourea (0.5 mol, 38 g) and 98% hydrazine hydrate (100 mL) were used as raw materials and the mixture was refluxed in a water bath for 3 hours. After completion of the reaction, the reaction mixture was cooled and diluted with 150 mL of distilled water. Subsequently, 10 mL of 2M HCl was added to neutralize to pH about 6.5 and frozen at 0 °C for 30 min. The crude product was obtained by filtration, washed with cold water and dissolved in 375 mL of 2M HCl and digested for 15 minutes. After removal of acid-insoluble impurities, the filtrate was neutralized to pH about 6.5 with NaOH and again frozen at 0°C. The solid product was gradually precipitated, filtered, washed several times with water, dried and recrystallized from water to give 4-amino-5-hydrazino-4H-[1,2,4]-triazole-3-thiol (1) as a white solid (24 g, 65% yield); melting point 244-246 °C (literature values 231-233 °C); FTIR (cm-1) 3439, 3262, 3185, 3076, 3014, 2915, 1638; 1H NMR (400 MHz, DMSO-d6) δ 12.70 (s, 1H, SH), 7.15 (s, 1H, NH), 5.28 (s, 2H, NH2), 4.15 (s, 2H, NH2-hydrazinyl); 13C NMR (100 MHz, DMSO-d6) δ 164.9, 155.1; Elemental analysis calculated values (C2H6N6S, 146): C, 16.43; H, 4.14; N, 57.49. Measured values: C, 16.48; H, 4.01; N, 57.36.
