(2) Preparation of 5-methyl-1,3,4-oxadiazolone: 2000 mL of methyl acetate was added to a 5000 mL three-necked flask and 740 g of acetylhydrazine was added slowly under stirring conditions. The reaction mixture was cooled to below 0 °C, followed by the addition of 1680 g of sodium bicarbonate in batches. The reaction unit was sealed and the phosgene was continuously vented at a flow rate of 15 m3/h. After completion of the reaction, the solvent was removed by distillation and the resulting residue was crystallized at 0 °C. The white crystals were collected by filtration to give 988.2 g of the target product in 99% yield.
