Example 2 Synthesis of 1,2,4-triazolin-5-one: A mixture of aminourea hydrochloride (10.0 g, 89.6 mmol), trimethyl orthoformate (28.5 g, 269 mmol), and methanol (100 mL) was stirred for 2 hours at room temperature. Upon completion of the reaction, the solvent was removed by concentration under reduced pressure. Subsequently, toluene (100 mL) was added to the concentrate and the mixture was cooled to 0°C. The precipitate was collected by filtration to afford 1,2-dihydro-3H-1,2,4-triazol-3-one (7.26 g, 100% yield) as a white solid. The structure of the product was confirmed by 1H NMR (d6-DMSO) and 13C NMR (d6-DMSO): 1H NMR δ= 7.66 (1H, s, CH), 11.24 (1H, s, NH) and 11.35 (1H, s, NH); and 13C NMR δ= 137.0 (CH2C=N) and 156.6 (NHCONH).
