Synthetic Routes to the Inorganic Azides

Making inorganic azides in the laboratory does not involve complicated reaction mechanisms or multistep syntheses as will be seen, the majority are accessible through straightforward metathetic reactions with NaN3 and HN3. Problems of a purely experimental nature may arise, however, whenever polymorphic forms of a species exist or differences in particle size or shape unexpectedly enhance the sensitivity of the sample. The effect may be quite drastic, as the following example shows, and cannot easily be predicted from general rules on chemical stability. 

The N3 group is always synthesized by reacting two compounds, one containing the —N=N— group and the other a single N. In principle, all oxidation states of nitrogen from -3 to +5 should be suitable for this approach, either in the form of the parent compounds themselves or, where applicable, as derivatives. In the latter case, both the —N=N— and N may be contained in the same molecule. Of the various possibilities (see Table III), the following combinations have been successfully used for azide syntheses a + b, a + e, b + b, b + c, b + g, 

Curtius discovered HN3 [1] by reacting benzoylhydrazine with nitrous acid (b + g-type reaction). The resulting benzoyl azide was saponified, and sodium azide was isolated from the alkaline mixture. In 1903 Wislicenus [14] synthesized sodium azide solely from inorganic compounds, namely, sodium metal, ammonia, and dinitrogen oxide (a + e). The reaction proceeds in two steps, first converting ammonia with sodium to sodamide, and then reacting this with dinitrogen oxide to yield sodium azide. Fifty percent of the sodamide is decomposed to hydroxide and ammonia, and the overall balance of the process is 

Wislicenus conducted the synthesis as a dry procedure at elevated temperature a low-temperature procedure in liquid ammonia was later patented by Acken and Filbert [15]. Although inherently only 50% effective, both versions have otherwise excellent yields and are now almost exclusively used for the manufacture of sodium azide. 

Darapsky [16] synthesized azide by oxidizing hydrazodicarbonamide with hypochlorite, an (a + b) reaction with both nitrogen species in the same molecule. Hydrazine, also discovered by Curtius, is the starting material in several other azide syntheses. One of these processes, independently invented by Thiele [17] and Stolle [18] and patented by the latter, uses nitrous acid or nitrites as an oxidant (b + g reaction type)  

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