Hydrazine hydrate (I) is added dropwise under stirring to ethyl acetoacetate (II), which has been heated to 140 C, water and ethanol formed in the reaction are distilled off, and the mixture is heated at reflux. Upon completion of the reaction, the mixture is allowed to stand at room temperature, and the solid thus separated is collected and recrystallized from ethanol to obtain the title compound.
Suspension of 3-methyl-2-pyrazolin-5-one (I) is added dropwise under stirring to ethyl acetoacetate (II), which has been heated to 140 C, water and ethanol formed in the reaction are distilled off, and the mixture is heated at reflux. Upon completion of the reaction, the mixture is allowed to stand at room temperature, and the solid thus separated is collected and recrystallized from ethanol to obtain the title compound.