Alkali- and Alkaline-Earth Azides

Asbestos, platinized, 1 160 3 129 Atomic weight, determination of average, of rare earth elements in a mixture, 2 58 Azides, alkali and alkaline earth, 1 79 2 136, 139... 

All the azides are potentially dangerous, and liable to detonate on heating, but those of the alkali and alkaline earth metals can be heated with caution if pure they then evolve pure nitrogen. 

Sr(N,)a is not discussed by Sax (Ref 24) but its effects should be considered similar to those of the alkali and alkaline earth azides Sr azide was first prepd in 1898 by Dennis Benedict (Ref 1) and in the same year by Curtius Rissom (Ref 2) by the action of... 

Sr(N3)j is not discussed by Sax (Ref 24) but its effects should be considered similar to those of the alkali and alkaline earth azides Sr azide was first prepd in 1898 by Dennis Benedict (Ref 1) and in the same year by Curtius Rissom (Ref 2) by the action of HNj on the oxide, hydroxide or carbonate of Sr. Its prepn has also been described by Mellor (Ref 7), Gmelin (Ref 9), Audrieth (Ref 10) and others (Refs 11, 15, 18, 19 25). The cryst structure of Sr(N3)2 was investigated to a limited extent by A.C.Gill (cited in Ref 1) and in detail by Llewellyn Whitmore (Ref 15) who established its orthorhmb nature as ionic, with a linear sym azide ion, N N 1.12A, and Sr to N distance of 2.63 to 27lX. Kahovec Kohlrausch (Ref 16) detd, from the Raman Effect, both on cryst powd and in soln, frequencies which corresponded to sym. oscillation in a linear triatomic molecule. 

Only the preparation of potassium azide is described here. However, the method outlined below can be adapted to the preparation of the alkali and alkaline earth azides in general. It is also suggested for the purification of technical sodium azide. The usual methods for the synthesis of sodium azide by the nitrous oxide-sodium amide3 method or the hydrazine-alkyl nitrite4 procedure have either not... 

A 3 per cent solution of hydrazoic acid (synthesis 26A) is neutralized with an aqueous solution of pure potassium hydroxide. The resulting solution of potassium azide is concentrated on the steam bath to incipient crystallization. The solution is then made slightly acid with hydrazoic acid to replace the hydrogen azide lost by hydrolysis. A volume of ethyl alcohol twice that of the solution is added, and the solution is cooled in an ice bath. Since the solubility in alcohol of the alkali and alkaline earth azides is very slight (see table below), precipitation in the form of a white microcrystalline salt takes place readily. From 90 to 95 per cent recovery of the theoretical quantity of potassium azide can be effected. The precipitated azide is filtered on a Buchner funnel and washed with cold absolute alcohol and then with ether. Any traces of adhering solvent may be removed in a vacuum desiccator. In a typical run, 300 ml. of a solution of hydrazoic acid containing 8.5 g. of HN3 was neutralized with potassium hydroxide, and the isolation of potassium azide effected as indicated above. Yield 14.7 g. (91.5 per cent) KN3. 

Thiatriazole-5-thiol is a fairly strong acid and its salts are readily obtained from the water-soluble alkali and alkaline earth azides with CS2 at 40 °C (equation 43) (64AHC(3)263). These should be handled with care. The potassium salt may explode violently when spread on a porous plate and the slightly soluble heavy-metal salts are very sensitive to shock even under water. An improved method for the preparation and storage of sodium thiatriazole-5-thiolate has been reported (74MI42800). l,2,3,4-Thiatriazole-5-thiol is prepared by addition of concentrated hydrochloric acid to a chilled solution of the sodium salt, obtained as a white or slightly yellow crystalline compound. The free acid can also be prepared from hydrazoic acid and carbon disulfide (equation 43) (64AHC(3)263). 

Form C for the acid, however, contains two adjacent atoms having positive formal charges whereas form C for the anion does not. If we consider structures containing adjacent atoms of like charge as inadmissible, then covalent azides should have but two forms as compared with three for ionic azides. While such a correlation may be far fetched, azide behavior is predicted correctly. Azides of the alkali and alkaline-earth metals (ionic azides) decompose at much higher temperatures than do azides of the heavy metals or hydrazoie acid itself (which are predominately covalent). Similarly, simple organic azides such as methyl azide, CH3N3, for which only two admissible forms may be drawn tend to be less stable than acid... 

The salts of hydrazoic acid, the azides, have similar properties as the respective chlorides, for example, AgNs, Hg2(N3)2, Pb(N3)2, CuNs, TIN3 have only low solubility in water. The alkali- and alkaline earth azides have ionic structures. With the exception of CsNs (m.p. 483 K), they do not melt without decomposition. Upon heating, they decompose under evolution of dinitrogen. 

Alkali and alkaline-earth metals Alkali-metal alkoxides Antineoplastic alkylating agents Aromatic amines Azides... 

The azides of the alkali and alkaline-earth metals are colourless crystalline salts which can almost be melted without decomposition taking place. X-ray studies have been made of several ionic azides (Li, Na, K, Sr, Ba ) they contain linear symmetrical ions with N—N close to 1-18 A. (A number of azides MN3 are isostructural with the difluorides MHF2.) Other azides which have been prepared include B(N3)3, A1(N3)3, and Ga(N3)3 from the hydrides, Be(N3)2 and Mg(N3)2 from M(CH3)2 and HN3 in ether solution, and Sn(N3)4 from NaN3 and SnCl4. 

Besides alkali halides, alkali and alkaline earth azides have been most thoroughly inveistigated for radiation coloration. By irradiation of freshly precipitated potassium azide at 196°C with radiation of A = 2537 A, Tompkins and Young19 obtained bands due to the presence of F-centres and V-centres. Ageing was found to have marked influence on these bands. The proposed mechanism of ageing involves the formation of anion and cation vacancy pairs... 

Recent photolysis studies considered the effect of the wavelength on the rate curve [207,212,213]. Specifically, photolysis of alkali and alkaline-earth azides using a low-pressure mercury lamp gave curves (Figure 26) whose characteristic shape was sensitive to the spectral content of the photolyzing light [198,207]. If the 180-nm line was filtered from the output spectrum of a low-pressure... 

The observed decomposition rate vs. time curves (already discussed for the alkali and alkaline-earth azides) show an initial deceleration in the rate. This may be surface desorption or, as suggested previously, may be a consequence of a reaction occurring at sites that are consun>ed as the decomposition proceeds. 

The indicated chemical reactions are not the only ones that because of strongly exothermic performance might be used for chemical dispersion—the decomposition of alkali and alkaline-earth azides being one other example. However, since this subject is at the moment merely speculative in the possible application to space exploration, the examples given should suffice to indicate approaches... 

The properties of the alkali and alkaline earth azides are discussed in Vol. 1 of tills series. ... 

The reaction can be done in a fused salt. Cyanides, cyanates and azides of alkali and alkaline earth metals are easily soluble in eutectic LiCl/KCl or ZnCl2/KCl mixtures. If the electrolytic dissociation of salts in the melt is complete, the anions react easily with haloorganosilanes introduced in gaseous form. Isothiocyanatoorganosilane can be prepared in a eutectic mixture of sodium and potassium thiocyanates. Fig. 3.3 shows an apparatus for the preparation of organopseudohalosilanes in a fused salt mixture [192, 193]. 

Tokumoto, M., Tanaka, Y., Kinoshita, N., Kinoshita, X, Ishibashi, S., and lhara, H., Characterization of the superconducting alkali and alkaline earth fullerides prepared by thermal decomposition of azides, J. Phys. Chem. Solids, 54, 1667, 1993. 

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