1. In a 100 mL reaction flask, formic acid (24.2 g, 0.52 mol), water (25 mL) and aminothiourea (20 g, 0.22 mol) were added sequentially. The mixture was heated to 105 °C and the reaction was maintained for 30 min.
2. Upon completion of the reaction, the reaction solution was slowly cooled to room temperature and subsequently placed at -10°C for slow crystallization.
3. Upon completion of crystallization, the solid product was collected by filtration and dried to afford aldimine thiourea (22.3 g white solid, 85% yield).
4. To a 250 mL single-necked flask was added aldimine thiourea (12 g, 0.1 mol), water (130 mL) and sodium carbonate (21.2 g, 0.25 mol). The mixture was heated to 100 °C and the reaction was kept for 4 hours.
5. At the end of the reaction, the reaction solution was slowly cooled to room temperature and the pH was adjusted to 4-5 with dilute hydrochloric acid.
6. The reaction solution was placed at -10°C with slow stirring to induce slow precipitation of the product. 7.
7. The solid product was collected by filtration and dried to give 3-mercapto-1,2,4-triazole (5.6 g white solid, 55% yield).
