Great Energetics Paper #1: Growing Catenated Nitrogen Atom Chains
This is the first post of what will be a regular occurrence on ExploSci.com, brief reviews of some of the most interesting new and old energetics chemistry.
Today’s paper by Q. Zhang and J. M. Shreeve is a highlight of recent work in the community where compounds containing increasing-length nitrogen chains are prepared.
We have some really attractive structures in this paper. On the shorter nitrogen chain-side we have the 1,3-bis(nitroimido)-1,2,3-triazolate anion as well as 1H-tetrazolo[1,5-d]tetrazole with both seven contiguous nitrogen atoms. The former is a unique illustrator of the alternating positive negative charge (APNC) theory, and the latter is a unique azidotetrazole isomer available from the treatment of 1,4-diaminotetrazole with sodium nitrite. Salts of the 1,3-bis(nitroimido)-1,2,3-triazolate anion can be exceedingly powerful; the hydroxylammonium salt has a detonation velocity of 9426 m / s.
As the nitrogen chains get longer, 1,1′-azobis(1,2,3-triazole) and 2,2′-azobis(5-nitrotetrazole) are mentioned, both of which have 8-nitrogen chains. The former is only about as sensitive as PETN with 68.3 % nitrogen and is stable up to 194 degrees Celcius. The latter likes spontaneously exploding when dry.
As the nitrogen chains get longer, are covered, both of which contain chains of ten nitrogen atoms. The former is 84.3 % nitrogen and explodes from only minor stimuli with a detonation velocity higher than that of RDX. Introduction of the methyl group in the latter results in an incresed thermal stability and a decreased sensitivity towards impact. Of course, the extra methyl group destroys the detonation velocity and brings it down to 7320 m / s.
Finally, we reach the current record holder for longest nitrogen chain. In the previous examples of N8 and N10 compounds, they were prepared by azocoupling the corresponding N-amino heterocycle with sodium dichloroisocyanurate. However the treatment of 1,5-diaminotetrazole with sodium nitrite under acidic conditions resulted in the formation of a diazonium species which then azo coupled with unreacted DAT giving a species containing a N11 chain. Unlike the previous compounds, this was not isolated pure, but rather as the chloride salt in a cocrystal with 5-aminotetrazole. Naturally, the cocrystalization with insensitive 5-aminotetrazole decreased the impact sensitivity to 10 J, far less sensitive than the previously mentioned shorter-chained compounds.
Just for fun, here is a video of the 1,1′-azobis(tetrazole)