Example 7 Preparation of 5-methoxy-4-methyl-2,4-dihydro-1,2,4-triazol-3-one: 4.77 g (25.0 mmol) of methyl N'-dimethoxymethylidenehydrazine carboxylate (85% purity) was mixed with 15.3 g of 51% methanol solution of methylamine (containing 250 mmol of methylamine), and stirred at room temperature for 3 days. After completion of the reaction, the orange-red solution was concentrated under reduced pressure to remove excess methylamine to give the crude product methyl N'-(methoxymethylaminomethylene) hydrazine carboxylate. The crude product was dissolved in 15 ml of methanol, 4.95 g (27.5 mmol) of a methanolic solution of 30% sodium methanolate was added, and the reaction was heated to 50 °C for 3 h 50 min. After the reaction mixture was cooled to room temperature, it was neutralized with 2N HCl and concentrated under reduced pressure. The residue was dissolved in 6 ml of water and placed in a refrigerator overnight for crystallization. Colorless crystals were collected by filtration, washed with cold water and dried under reduced pressure to give 1.70 g (52.7% yield) of 5-methoxy-4-methyl-2,4-dihydro-1,2,4-triazol-3-one as a colorless solid with a melting point of 146-148 °C.
