Azides of Zinc

The normal azide, Zn(N3)2, is a white, sandy powder which is hygroscopic and has a strong tendency to decompose hydrolytically. Thus, the odor of HN3 appears immediately when the solid is exposed to atmospheric moisture, and in time aqueous solutions separate voluminous precipitations of basic products. These basic salts are inherently poorly defined, and the basic zinc azides and zinc hydroxyazides of the literature may have analyses anywhere between Zn(N3)2 and Zn(OH)2. Nevertheless, two discrete phases of the composition (OH)Zn(N3) and Zn3(OH)s Zn2(N3) were determined by X-ray analysis, but the method of preparing them was not given [160]. Recently, the existence of a dihydrate, Zn(N3)2 2H2O, has been suggested, with a dehydration point at 27.5°C[211]. 

Zinc azide explodes on impact but is markedly less sensitive than other heavy metal azides [54] in a flame it deflagrates [54]. The temperature of explosion is near 289°C [85,115]. Basic zinc azides also explode [116]. 

It appears that pure zinc azide has never been isolated, because all wet methods of preparation involved water at some stage. For example, zinc metal was dissolved in hydrazoic acid the solution supposedly contained zinc azide but separated basic salts on standing [62]. Zinc carbonate was also suspended in ethereal hydrazoic acid and agitated at room temperature for 3 days. The product was then extracted with cold water to yield an azide which was not free of H and O [54, 143]. Basic products were also obtained by distilling hydrazoic acid onto zinc carbonate [212] or hydroxide [116], or by reacting zinc sulfate and barium azide solutions [73]. Hydrolysis in these aqueous solutions maybe retarded by precipitating the azide with acetone [213]. 

Using the dry Wislicenus process, N-doped zinc azide was made by reacting zinc amide with nitrous oxide at 180°C for 96 hr [85]. The product can be considered pure Zn(N3)2, but an equimolar amount of zinc hydroxide is admixed which was not separated. 

A tetraazidozincate anion, [Zn(N3)4] , was isolated as the cesium, tetra-ethylammonium, and tetraphenylphosphonium salts. It appears to be stable in aqueous media, as aquation or hydrolytic decomposition have not been reported. In fact, the cesium salt grows into large crystals from aqueous solutions. The compounds are white solids which are not impact sensitive depending on the nature of the cation, they are soluble in water or polar organic solvents. 

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