Azidotetrazole Salts

Out of the whole range of 5-halotetrazole salts, only the cupric salt of 5-chlorotetrazole has found a use—e.g., in primers for space applications [1]. Many other metallic salts of 5-chlorotetrazole (e.g., silver salt) have been disqualified from application mainly due to their high mechanical sensitivity [76]. 

5-Azido-l//-tetrazole (subsequently just 5-azidotetrazole) forms monoclinic colorless needles with a theoretical maximum density 1.72 g cm. Melting point is 75 °C [77]. It is, just like its alkali metal salts, soluble in water, acetone, ether, and ethanol. Lead, mercury, and silver salts are insoluble in these solvents [1,78], The potassium salt of 5-azidotetrazole is stable in aqueous and alcoholic solutions, but it explodes spontaneously if traces of acetic acid are present, even in acetone solution [78], The 5-azidotetrazoles are fairly stable in storage when in the pure state [1], 

Free 5-azidotetrazole is reported in Fedoroff, Sheffield, and Kaye s encyclopedia as less sensitive to impact than its alkaline salts [1], Other authors reported 5-azidotetrazole as a highly sensitive compound [2, 77]. Stierstorfer et al. [77] reported sensitivity to impact below 1 J, sensitivity to friction below 5 N, and sensitivity to electrostatic discharge 2.2 mJ. 5-Azidotetrazole melts and decomposes at 165 °C when heated with heating rate 5 °C min [77]. Pure 5-azidotetrazole is fairly stable in storage. However, it may spontaneously explode in presence of some impurities especially in presence of traces of acetic acid (it can explode even in acetone solution explosions do not occur in aqueous or ethanol solutions) [1]. 

Sensitivities of the silver and potassium salts are extremely high. The potassium salt can even be detonated by touching it with a spatula [1]. The cesium salt is another very sensitive compotmd which is, together with the potassium salt, reported to be a substance which cannot be handled without violent explosion [77]. On the other hand, the published value for impact sensitivity of the barium salt is 35 cm/0.5 kg (A50) [1]. Friedrich published an impact sensitivity for 1 kg hammer of 3 cm for the copper salt and 3-5 cm for the cadmium salt [79]. The lead salt detonates when touched with a flame [1]. 

Metallic salts of 5-azidotetrazole are brisant primary explosives (even amounts as small as 10 mg of the potassium salt can cause damage) [1]. Initiating efficiency of these substances is high an amount of only 1-2 mg is sufflcient to initiate PETN [80]. 

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Table 8.12 Selected expeiimental properties of 5-azidotetrazole salts [83]...

The reaction of aminoguanidine with sodium nitrite under neutral conditions yields tetra-zolylguanyltetrazene hydrate (85), a primary explosive commonly known as tetrazene. Tetrazene (85) is only formed in the absence of free mineral acid and so a common method for its preparation treats the bicarbonate salt of aminoguanidine (84) with one equivalent of acetic acid followed by addition of aqueous sodium nitrite. " Tetrazene (85) is decomposed by aqueous alkali to form triazonitrosoaminoguanidine (86) which is isolated as the cuprate salt (87) on addition of copper acetate to the reaction mixture. Acidification of the copper salt (87) with mineral acid leads to the formation of 5-azidotetrazole (88) (CHN7 = 88 % N).55 56... 

The salts of 5-Nitrotetrazole could also be ranked according to their sensitiveness. The salts of Ag, Hg, and Pb gave more sensitive compns and greater initiating power than the alkali metal salts. The same salts of 5-Chloro-tetrazole were too sensitive and corrosive, and those of 5-Azidotetrazole were too hazardous (Ref 9b)... 

Perhaps the most exotic imidoyl azide, containing the imido function as part of a heteroaromatic system, is b-azidotetrazole, HGN7, the potassium and sodium salts of which are obtained when 1,3-diamino-guanidine (imidocarbazide) is treated with alkali nitrites in acetic acid ". The alkali salts, Na+ and K CN7, are extremely explosive, the free azide less so. It shows the i.r. absorption of the azide group at 2151 cm ... 

ACETIC ACID, AMMONIUM SALT (631-61-8) Violent reaction with strong oxidizers, ammonium nitrate, chlorine trifluoride, magnesium, potassium nitrite, sodium chlorate, sodium hypochlorite. Incompatible with nitrates. Forms a heat-sensitive explosive with 5-azidotetrazole. Reacts with gold chloride, forming fulminating gold, a heat-, friction-, and impact-sensitive explosive. Incompatible with sodium dichloroisocyanurate. 

SODIUM DICHLORISOCYANURATE (2893-78-9) Not combustible, but will enhance the activity of fire. Reacts violently with water, steam, releasing chlorine gas. A powerful oxidizer. Reacts violently with reducing agents, combustible materials, organic substances, powdered metals, organic nitrites, easily chlorinated or oxidized materials. Incompatible with sodium hypochlorite, ammonium salts, amines. May form explosive product with ammonium nitrate, 5-azidotetrazole. 

The preparation of cyanogen azide from cyanogen bromide and sodium azide in anhydrous medium has recently been described.339 In aqueous solution, further involvement of a second azide ion leads to the sodium salt of 5-azidotetrazole.339 The influence of solvent on these reactions... 

Azidotetrazole can be prepared by several methods. The simplest method is the direct cycloaddition reaction between alkaline azides and cyanogen halogen. An alkaline salt of 5-azidotetrazole forms according to the following reaction [81,82] ... 

The reaction is carried out in an aqueous solution and at low temperatures sodium azide may be used as well [77]. The resulting salt can be converted to free 5-azidotetrazole by hydrochloric acid [83]. 

Another way of preparing 5-azidotetrazole is based on the diazotization reaction. 5-ATZ is mostly used as the starting material. Tetrazole diazonium salt forms as an intermediate which is converted into the desired tetrazole azide by treatment with sodium azide [84]. 

Diaminoguanidine is another possible starting material which can be used for preparation of 5-azidotetrazole and its salts. It forms when diaminoguanidine nitrate is treated with two moles of nitrous acid in an acetic acid solution [78]. 

Various salts of 5-azidotetrazole can be prepared by treating it with relevant salts [78]. Preparation, crystallographic studies, and characterization of hydrazinium, ammonium, aminobiguanidinium, guanidinium, lithium, sodium, potassium, cesium and calcium salts of 5-azidotetrazole were described by Klapotke and Stierstorfer [83]. Some experimental data from this paper are summarized in Table 8.12. The guanidinium salt forms as a semihydrate, whereas the lithium and sodium salts of 5-azidotetrazole form hydrates. The structure of the calcium salt is more complicated as it forms a complex with the following formula [Ca(CN7)2(H20)io] [Ca(H20)6](CN7)2. 

Despite the high initiating efficiency of many metallic salts of 5-azidotetrazole, most of them are too sensitive for practical use. 

Table 8.19 Impact sensitivities of organic derivatives of 5-azidotetrazole in comparison with the cupric and cadmium salts of 5-azidotetrazole [79]...

Organic derivatives of 5-azidotetrazole have been reported by Friedrich [99]. They are more stable and less sensitive than the metallic salts. The methyl and ethyl derivatives are very strong igniting explosives. Ethylene tetrazylazide, that forms an oily liquid, possesses extraordinary brisance and is easily ignited by spark and flames. It easily gelatinizes nitrocellulose [1,99]. Impact sensitivities of 5-azido-l-methyltetrazole and 5-azido-l-picryltetrazole in comparison with the copper salt are summarized in Table 8.19 [79]. 

Organic derivatives of 5-azidotetrazole can be prepared from the alkali salts of 5-azidotetrazole and organic chlorides of sulfates [99]. 

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