Chemistry:Azide
In chemistry, azide (/ˈeɪzaɪd/, AY-zyd) is a linear, polyatomic anion with the formula N−
3 and structure −
N=N+
=N−
. It is the conjugate base of hydrazoic acid HN
3. Organic azides are organic compounds with the formula RN
3, containing the azide functional group.[1] The dominant application of azides is as a propellant in air bags.[1]
Preparation
Sodium azide is made industrially by the reaction of nitrous oxide, N
2O with sodium amide NaNH
2 in liquid ammonia as solvent:[2]
- [math]\ce{ N2O + 2 NaNH2 -> NaN3 + NaOH + NH3 }[/math]
Many inorganic azides can be prepared directly or indirectly from sodium azide. For example, lead azide, used in detonators, may be prepared from the metathesis reaction between lead nitrate and sodium azide. An alternative route is direct reaction of the metal with silver azide dissolved in liquid ammonia.[3] Some azides are produced by treating the carbonate salts with hydrazoic acid.
Bonding
Azide is isoelectronic with carbon dioxide CO
2, cyanate OCN−
, nitrous oxide N
2O, nitronium ion NO+
2, molecular beryllium fluoride BeF
2 and cyanogen fluoride NCF. Per valence bond theory, azide can be described by several resonance structures; an important one being N−
=N+
=N−
Reactions
Azide salts can decompose with release of nitrogen gas. The decomposition temperatures of the alkali metal azides are: NaN
3 (275 °C), KN
3 (355 °C), RbN
3 (395 °C), and CsN
3 (390 °C). This method is used to produce ultrapure alkali metals:[4]
- 2 MN
3 2 M + 3 N
2
Protonation of azide salts gives toxic hydrazoic acid in the presence of strong acids:
- H+
+ N−
3 → HN
3
Azide as a ligand forms numerous transition metal azide complexes. Some such compound are more shock sensitive.
Many inorganic covalent azides (e.g., chlorine, bromine, and iodine azides) have been described.[5]
The azide anion behaves as a nucleophile; it undergoes nucleophilic substitution for both aliphatic and aromatic systems. It reacts with epoxides, causing a ring-opening; it undergoes Michael-like conjugate addition to 1,4-unsaturated carbonyl compounds.[1]
Azides can be used as precursors of the metal nitrido complexes by being induced to release N
2, generating a metal complex in unusual oxidation states (see high-valent iron).
Disposal
Azides decompose with nitrite compounds such as sodium nitrite when acidified. This is a method of destroying residual azides, prior to disposal.[6] In the process, nitrogen, nitrogen oxides, and hydroxides are formed:
- 3 N−
3 + NO−
2 + 2 H
2O → 5 N
2 + 4 OH−
- N−
3 + 7 NO−
2 + 4 H
2O → 10 NO + 8 OH−
Applications
About 251 tons of azide-containing compounds are produced annually, the main product being sodium azide.[7] Sodium azide NaN
3 is the propellant in automobile airbags. It decomposes on heating to give nitrogen gas, which is used to quickly expand the air bag:[7]
- 2 NaN
3 → 2 Na + 3 N
2
Heavy metal azides, such as lead azide, Pb(N
3)
2, are shock-sensitive detonators which decompose to the corresponding metal and nitrogen, for example:[8]
- Pb(N
3)
2 → Pb + 3 N
2
Silver azide AgN
3 and barium azide Ba(N
3)
2 are used similarly. Some organic azides are potential rocket propellants, an example being 2-dimethylaminoethylazide (DMAZ) (CH
3)
2NCH
2CH
2N
3.
Safety
Azides are explosophores[9][10] and poisons. Sodium azide is as toxic as sodium cyanide (with an oral -1">50 of 27 mg/kg in rats) and can be absorbed through the skin. Heavy metal azides, such as lead azide are primary high explosives detonable when heated or shaken. Heavy-metal azides are formed when solutions of sodium azide or HN
3 vapors come into contact with heavy metals or their salts. Heavy-metal azides can accumulate under certain circumstances, for example, in metal pipelines and on the metal components of diverse equipment (rotary evaporators, freezedrying equipment, cooling traps, water baths, waste pipes), and thus lead to violent explosions.
See also
- Pentazenium
- Pentazolate (cyclo-N−
5)
References
- ↑ 1.0 1.1 1.2 S. Bräse; C. Gil; K. Knepper; V. Zimmermann (2005). "Organic Azides: An Exploding Diversity of a Unique Class of Compounds". Angewandte Chemie International Edition 44 (33): 5188–5240. doi:10.1002/anie.200400657. PMID 16100733.
- ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 433. ISBN 978-0-08-037941-8.
- ↑ Müller, Thomas G.; Karau, Friedrich; Schnick, Wolfgang; Kraus, Florian (2014). "A New Route to Metal Azides". Angewandte Chemie 53 (50): 13695–13697. doi:10.1002/anie.201404561. PMID 24924913.
- ↑ Dönges, E. (1963). "Alkali Metals". in Brauer, G.. Handbook of Preparative Inorganic Chemistry. 1 (2nd ed.). NY: Academic Press. p. 475.
- ↑ I. C. Tornieporth-Oetting; T. M. Klapötke (1995). "Covalent Inorganic Azides". Angewandte Chemie International Edition in English 34 (5): 511–520. doi:10.1002/anie.199505111.
- ↑ Committee on Prudent Practices for Handling, Storage, and Disposal of Chemicals in Laboratories, Board on Chemical Sciences and Technology, Commission on Physical Sciences, Mathematics, and Applications, National Research Council (1995). Prudent practices in the laboratory: handling and disposal of chemicals. Washington, D.C.: National Academy Press. ISBN 0-309-05229-7. http://books.nap.edu/openbook.php?record_id=4911&page=165.
- ↑ 7.0 7.1 Jobelius, Horst H.; Scharff, Hans-Dieter (2005). "Hydrazoic Acid and Azides". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a13_193. ISBN 3527306730.
- ↑ Shriver; Atkins. Inorganic Chemistry (5th ed.). New York: W. H. Freeman and Company. p. 382.
- ↑ Treitler, Daniel S.; Leung, Simon (2 September 2022). "How Dangerous Is Too Dangerous? A Perspective on Azide Chemistry" (in en). The Journal of Organic Chemistry 87 (17): 11293–11295. doi:10.1021/acs.joc.2c01402. ISSN 0022-3263. PMID 36052475. https://pubs.acs.org/doi/10.1021/acs.joc.2c01402. Retrieved 18 September 2022.
- ↑ Mandler, Michael D.; Degnan, Andrew P.; Zhang, Shasha; Aulakh, Darpandeep; Georges, Ketleine; Sandhu, Bhupinder; Sarjeant, Amy; Zhu, Yeheng et al. (28 January 2022). "Structural and Thermal Characterization of Halogenated Azidopyridines: Under-Reported Synthons for Medicinal Chemistry". Organic Letters 24 (3): 799–803. doi:10.1021/acs.orglett.1c03201. PMID 34714083.
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