In a 3-l. round-bottomed flask equipped with a reflux condenser are placed 582 g. (2.5 moles) of N-tricarboxylic ester (p. 415) and 800 g. (6.7 moles) of 42% hydrazine hydrate (Note 1). The flask is shaken by hand to mix the two layers. After a short time, reaction begins with considerable evolution of heat, and all the N-tricarboxylic ester goes into solution (Note 2). After the reaction subsides, the solution is heated for 1 hour on a steam bath and then evaporated under reduced pressure until the mixture becomes a thick slurry of diaminobiuret crystals (Note 3). The mixture is cooled, 2 l. of 95% ethanol is added, and the diaminobiuret which has crystallized is filtered, washed with 250 ml. of ethanol, and dried. The substance melts at 205° with decomposition. The yield is 115–125 g. (69–75%).

The filtrate is now evaporated at atmospheric pressure to remove the ethanol, and the residual oil is distilled using a Vigreux column. Ethyl hydrazinecarboxylate boils at 92–95° /13 mm. The yield is 350–370 g. (90–95%). After distillation in vacuum, the ester may crystallize; the crystals melt at 51–52°.