The Stabilisation of Hydrazine

Phthalyl hydrazide (48.6 g. ) was dissolved at 90°C. in aqueous hydrazine hydrate (292 cc. of a 16% w/v. solution 3.1 mol.). The solution was filtered and stirred into ethyl alcohol (800 cc.). The white bulky precipitated salt was collected at 0°C., washed with ethyl alcohol and dried over caustic potash at 25°C./25 mm., giving 43 g. (74%), m.p. 340-344°C. (Found N, 28.8%. Calculated for C8H602N2, N2H4 N, 28.85%. 

In the step of dissociating the phthalyl hydrazide salt there was used an apparatus consisting of an all-glass distillation flask immersed in a heating bath and sealed to a U-shaped receiver connected to an oil pump, there being constrictions in the two limbs of the receiver at which it could be sealed off and removed while still evacuated. Finely powdered anhydrous phthalylhydrazide salt of hydrazine (9.7 g.) was filled into the flask and covered with a plug of glass wool. The apparatus was evacuated to 0.01 mm. and the receiver placed in a solid carbon dioxide-acetone bath. The temperature of the salt was raised slowly to 180°C., by which time the anhydrous hydrazine had collected as a practically colourless solid, 1.47 g. (92% 99.5% pure by the iodate method described by Kolthoff, J.A.C.S. 1924, 46, 2009). 

The phthalylhydrazide salt employed in this example may also be prepared in the following manner — 

Hydrazine hydrate (25 cc. of a 50% w/v. aqueous solution 2.5 mol.) was added to a suspension of phthalimide (14.7 g.) in boiling ethyl alcohol (178 cc.). After 6 hours refluxing, the white bulky product was collected at 0°C. and washed with ethyl alcohol. The anhydrous salt (17.5 g. 90%) was obtained by drying this material over caustic potash at 25°C./25 mm. (Found N, 28.6%).Source Barber 1949 Ref Barber 1948 

It has now been discovered that the stability of concentrated hydrazine, particularly as prepared by the Raschig process and its corrosiveness to metals are associated with a property most simply explained as its potential acidity which can be neutralised, treating the hydrazine as the dissociating medium or solvent, by the addition of certain substances which are weakly basic and which are non-reactive with hydrazine. 

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