Azidotetrazolate Explained

Azidotetrazolate (CN7) is an anion which forms a highly explosive series of salts. The ion is made by removing a proton from 5-azido-1H-tetrazole. The molecular structure contains a five-membered ring with four nitrogen atoms, and an azido side chain connected to the carbon atom. Several salts exist, but they are unstable and spontaneously explode.[1] For example, the rubidium, potassium and caesium salts are so unstable that they explode while crystallizing.[1]

Azidotetrazolates are under investigation for use as bullet propellant, rocket propellants and high explosives. The nitrogen base compounds have the advantage of being "green explosives", meaning that their waste products are safe.[1] Amongst the tetrazolates, they have the highest nitrogen fraction.[2]

Properties

Different stimuli can set off explosions. Possibilities include impact, friction, sparks or heat. Guanidinium azidotetrazolate could be melted to an ionic liquid at 100°C, but would decompose smoothly at 159°. Sodium azidotetrazolate explodes when the temperature reaches 155°C.[1]

The CNNNN ring in azidotetrazolate is planar and aromatic. The NNN side chain is attached to the carbon atom, and bent at the first nitrogen so that it is roughly parallel to the ring.[3]

The base acids, 5-azido-1H-tetrazole and 5-azido-2H-tetrazole both can exist. The 1H version has a hydrogen atom bonded to a nitrogen atom next to the carbon. It is the stable form in solids and solutions in polar liquids. This is explained by a favourable hydrogen bond, and a greater dipole moment. The 2H version with hydrogen attached in the second nitrogen from the carbon is purportedly more stable in the gas phase.[4]

Formation

The azidotetrazolate ion can be made from cyanogen bromide and sodium azide in water:[1]

BrCN + 2NaN3 → N4CN3 + Na+ + NaBr

Salts

formulanamemolecular weightdensitystructureunit cell dimension Åcell volumeformula per cellSpecific impulsemelt °Cdecompose °CCAS[5]
NH4CN7Ammonium azidotetrazolate128.121.608monoclinica=3.9103 b=6.9140 c=9.9127 β=99.177°264.57224815735038-47-2
N2H5CN7Hydrazinium azidotetrazolate143.141.568monoclinica=10.8114 b=7.4641 c=7.6676 β=101.437°606.474265136
CN3H6CN7guanidinium azidotetrazolate semihydrate358.351.546monoclinica=9.5374 b=15.3120 c=10.5731 β=94.3611539.64100159
CN4H7CN7aminoguanidinium azidotetrazolate185.191.524triclinica=9.7652 b=9.7803 c=10.0434 α=71.327° β=74.399° γ=63.962°807.24228
NH3OHCN7Hydroxylammonium azidotetrazolate[6] 144.121.649monoclinica=3.677 b=20.885 c=7.641 β=98.367580.54
LiCN7•H2OLithium azidotetrazolate monohydrate135.031.683monoclinica=8.9207 b=4.6663 c=12.8648 β=95.608532.964
NaCN7•H2Osodium azidotetrazolate monohydrate151.091.743monoclinic a=11.203 b=7.138 c=14.409 β=91.630°1151.88explode15535038-45-0
KCN7Potassium azidotetrazolate149.181.917monoclinica=9.7759 b=6.2990 c=8.4533 β=96.720°516.964
RbCN7Rubidium azidotetrazolate195.12Unknown; all attempts at isolation terminated by detonation of solution.<25
CsCN7Caesium azidotetrazolate242.992.810orthorhombica=4.3082 b=7.1345 c=18.6869574.384
3Ca(CN7)2•16H2OCalcium azidotetrazolate1068.981.657monoclinica=24.448 b=6.616 c=28.057 β=109.246°42854
AgCN7silver azidotetrazolate
HCN75-Azido-1H-tetrazole111.071.727516535038-46-1

Related

Chemicals related to the azidotetrazolate anion include 1-diazidocarbamoyl-5-azidotetrazole with the same percentage of nitrogen.

External links

Notes and References

  1. Klapötke. Thomas M.. Stierstorfer. Jörg. The CN7- Anion. Journal of the American Chemical Society. 28 January 2009. 131. 3. 1122–1134. 10.1021/ja8077522. 19115947 .
  2. Web site: Petkewich. Rachel A.. High-Nitrogen Anion Exceeds The Power Of RDX January 12, 2009 Issue - Vol. 87 Issue 2 Chemical & Engineering News. cen.acs.org.
  3. Zhaoxu. Chen. Jianfen. Fan. Heming. Xiao. Theoretical study on tetrazole and its derivatives. Part 7: ab initio MO and thermodynamic calculations on azido derivatives of tetrazole. Journal of Molecular Structure: THEOCHEM. January 1999. 458. 3. 249–256. 10.1016/S0166-1280(98)00249-8.
  4. Stierstorfer. Jörg. Klapötke. Thomas M.. Hammerl. Anton. Chapman. Robert D.. 5-Azido-1H-tetrazole – Improved Synthesis, Crystal Structure and Sensitivity Data. Zeitschrift für anorganische und allgemeine Chemie. June 2008. 634. 6–7. 1051–1057. 10.1002/zaac.200800003.
  5. Marsh. F. D.. Cyanogen azide. The Journal of Organic Chemistry. September 1972. 37. 19. 2966–2969. 10.1021/jo00984a012.
  6. Klapötke. Thomas M.. Piercey. Davin G.. Stierstorfer. Jörg. The Taming of CN7−: The Azidotetrazolate 2-Oxide Anion. Chemistry - A European Journal. 11 November 2011. 17. 46. 13068–13077. 10.1002/chem.201102064. 21971954 .