Azides of Mercury

Hg(N3)2 is somewhat photosensitive and turns yellow in bright daylight, owing to the appearance of colloidal mercury. It also decomposes thermally [2], with gas evolution starting at 212°C, followed by discoloration at 220°C and explosion at 300°C. The compound is slightly soluble in cold water (0.257 g in 100 g solution at 20°C) [223] in hot water it dissolves more readily, without noticeable hydrolysis. It also dissolves in ethanolamine, apparently without chemical reaction [227], and in hydrofluoric acid, as a cation complex. Upon evaporation of the acid, the azide appears unchanged [196]. 

Hg(N3)2 has been made by dissolving mercury (II) oxide in hydrazoic acid [13,225,226]  

To separate the product from unreacted HgO, the azide is dissolved by heating and then filtered. It recrystallizes as the above-mentioned, highly sensitive needles which have to be handled with extreme caution e.g., a large particle, slowly sinking in a water-filled beaker, exploded when touching the bottom [13]. Likewise, crystals adhering to the wall could not be removed without explosion. It is essential to move the liquid constantly with a stirrer made of a soft material [13], as slow cooling of an unstirred solution leads invariably to explosion [224], 

The compact crystal form is prepared more safely by precipitating at room temperature a concentrated solution of mercury (II) nitrate or chloride with sodium azide. The product may be separated by centrifuging [12]. 

Among complex mercury(II) azides a colorless, explosive dipyridine diazido-mercury(II) of the possible structure [Hg (Py)2(N3)2] is precipitated when water is added to a solution of mercury(II) nitrate in pyridine [138]. A triazidomercurate(II), [Hg (N3)3] , is obtained from mercury(II) nitrate and excess sodium azide in acid media and isolated as the tetraphenylphosphonium salt [139,222,238]. 

---

Azides of mercury darken in color and start to decompose when heated above 212 °C. The decomposition process is accompanied by evolution of nitrogen prior to its explosion [80]. 

Table 4.13 Impact sensitivity, explosion temperature, and initiating efficiency to tetryl and TNT of azides of mercury, cadmium, and thallium and comparison with lead azide...

---