| Pentazole | |
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1H-Pentazole[1] |
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| Identifiers | |
| CAS number | 289-19-0 |
| PubChem | 6451467 |
| ChemSpider | 4953932 |
| Jmol-3D images | Image 1 Image 2 |
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| Properties | |
| Molecular formula | N5H |
| Molar mass | 71.0414 g mol-1 |
| Exact mass | 71.023195057 g mol-1 |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Pentazole is an aromatic chemical molecule consisting of a five-membered ring with all nitrogen atoms, one of which is bonded to a hydrogen atom. It has a molecular formula of HN5. Its SMILES structure is n1n[nH]nn1. Although strictly speaking a homocyclic, inorganic compound, pentazole has historically been classed as the last in a series of heterocyclic azole compounds containing one to five nitrogen atoms. This set contains pyrrole, imidazole, pyrazole, triazoles, tetrazoles, and pentazole. One can consider pentazole to be at the interface between inorganic and organic chemistry.
Substituted analogs of pentazole are collectively known as pentazoles. As a class, they are unstable and often highly explosive compounds. The first pentazole synthesized was phenyl pentazole, where the pentazole ring is highly stabilized by conjugation with the phenyl ring. The derivative 4-dimethylaminophenylpentazole is among the most stable pentazole compounds known, although it still decomposes at temperatures over 50°C. It is known that electron-donating groups stabilize aryl pentazole compounds.[2]
The cyclic pentazolium cation (N5+) is not known due to its probable antiaromatic character; whereas the open chained pentazenium cation (N5+) is known. The mass spectrometer signal for the pentazolide anion (N5-) has been detected from the decomposition of substituted phenyl pentazoles. There was a first report of the synthesis of pentazole and pentazole anion in solution [3][4] as evidenced by their 15N isotope labeled azide product, but the evidence for the formation of pentazole anion was disputed.[5] Later experiments that involved the detailed analysis of decomposition products demonstrated the generation of pentazole.[6] The experimental conclusions were supported by high level theoretical calculations.[7] However, pentazole is not expected to last longer than a few seconds in aqueous solution without the aid of complexing agents. The discovery of pentazoles spurred attempts to create all-nitrogen salts, which should be highly potent propellants for space travel.