HYDRAZINE AND ITS DERIVATIVES

Benzenediazonium chloride reacts with hydrazine to form phenyl azide and ammonia in greater than 90% The un- 

Much mechanistic detail has been elucidated, however, from reactions involving substituted hydrazines. For example, the proportion of N(i), N(2) to N(3), N(4) fission in the symmetrically substituted tetrazene formed from benzenediazonium chloride and phenyl-hydrazine (equation 127), has been shown to be almost statistical by N-labelling °. Rapid tautomeric exchange of the protons along the nitrogen chain of the tetrazene was thereby established. 

In reactions involving unsymmetrical diaryltetrazenes such as 238 four different products arise as a result of this statistical decomposition (equation 128). Horwitz and Grakauskas have discussed the mechanism of coupling between phenylhydrazine and benzenediazonium salts in detail. In mineral acid, little or no free base is present and the reaction should involve either, or both, of 

Azides may be formed by reaction of aryldiazonium salts with hydrazides. For example, from benzhydrazide and benzenedia-zonium sulphate the tetrazene (247) was isolated and subsequently decomposed to benzazide and phenyl azide (equation 129). 

Similarly, treatment of the anthranilic acid derivative (248) with nitrous acid gave the cyclic product 249 which underwent hydrolysis in aqueous alkali to afford o-azidobenzoic acid 1,2-Diacetylhydra- 

Hydrazine [302-01-2] (diamide), N2H4, a colorless liquid having an ammoniacal odor, is the simplest diamine and unique in its class because of the N—N bond. It was first prepared in 1887 by Curtius as the sulfate salt from diazoacetic ester. Thiele (1893) suggested that the oxidation of ammonia (qv) with hypochlorite should yield hydrazine and in 1906 Raschig demonstrated this process, variations of which constitute the chief commercial methods of manufacture in the 1990s. 

The first large-scale use of hydrazine was as fuel for the rocket-powered German ME-163 fighter plane during World War II. Production in the United States began in 1953 at the Lake Charles, Louisiana plant of the Olin Corp., a facility then having a capacity of 2040 metric tons. In 1992 world capacity was about 44,100 metric tons N2H4. 

The many advantageous properties of hydrazine ensure continued commercial utility. Hydrazine is available in anhydrous form as well as aqueous solutions, typically 35, 51.2, 54.4, and 64 wt % N2H4 (54.7, 80, 85, and 100% hydrazine hydrate). 

The freezing point diagram for the hydrazine—water system (Eig. 1) shows two low melting eutectics and a compound at 64 wt % hydrazine having a melting point of —51.6°C. The latter corresponds to hydrazine hydrate [7803-57-8] which has a 1 1 molar ratio of hydrazine to water. The anomalous behavior of certain physical properties such as viscosity and density at the hydrate composition indicates that the hydrate exists both in the Hquid as well as in the soHd phase. In the vapor phase, hydrazine hydrate partially dissociates. 

Ereezing-point diagram for hydrazine—water mixtures. 

---

Heterocyclics. One of the most characteristic and useful properties of hydrazine and its derivatives is the ability to form heterocycHc compounds. Numerous pharmaceuticals, pesticides, explosives, and dyes are based on these rings. A review of the appHcation of hydrazine in the synthesis of heterocychcs is available (91). For further information in the field of heterocycHc chemistry, see the General References. 

Numerous explosives are based on hydrazine and its derivatives, including the simple azide, nitrate, perchlorate, and diperchlorate salts. These are sometimes dissolved in anhydrous hydrazine for propeUant appUcations or in mixtures with other explosives (207). Hydrazine transition-metal complexes of nitrates, azides, and perchlorates are primary explosives (208). 

---