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Azide

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The azide anion

In chemistry, azide (/ˈzd/, AY-zyd) is a linear, polyatomic anion with the formula N3 and structure N=N+=N. It is the conjugate base of hydrazoic acid HN3. Organic azides are organic compounds with the formula RN3, containing the azide functional group.[1] The dominant application of azides is as a propellant in air bags.[1]

Preparation

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Sodium azide is made industrially by the reaction of nitrous oxide, N2O with sodium amide NaNH2 in liquid ammonia as solvent:[2]

N2O + 2 NaNH2 → NaN3 + NaOH + NH3

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

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Azide is isoelectronic with carbon dioxide CO2, cyanate OCN, nitrous oxide N2O, nitronium ion NO+2, molecular beryllium fluoride BeF2 and cyanogen fluoride FCN. Per valence bond theory, azide can be described by several resonance structures; an important one being N=N+=N

Reactions

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Azide salts can decompose with release of nitrogen gas. The decomposition temperatures of the alkali metal azides are: NaN3 (275 °C), KN3 (355 °C), RbN3 (395 °C), and CsN3 (390 °C). This method is used to produce ultrapure alkali metals:[4]

2 MN3 heat 2 M + 3 N2

Protonation of azide salts gives toxic hydrazoic acid in the presence of strong acids:

H+ + N3 → HN3

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 N2, generating a metal complex in unusual oxidation states (see high-valent iron).

Redox behaviour and trend to disproportionation

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Frost diagram for nitrogen species at pH = 0

Azides have an ambivalent redox behavior: they are both oxidizing and reducing, as they are easily subject to disproportionation, as illustrated by the Frost diagram of nitrogen. This diagram shows the significant energetic instability of the hydrazoic acid HN3 (or the azide ion) surrounded by two much more stable species, the ammonium ion NH+4 on the left and the molecular nitrogen N2 on the right. As seen on the Frost diagram the disproportionation reaction lowers ∆G, the Gibbs free energy of the system (-∆G/F = zE, where F is the Faraday constant, z the number of electrons exchanged in the redox reaction, and E the standard electrode potential). By minimizing the energy in the system, the disproportionation reaction increases its thermodynamical stability.

Disposal

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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 N3 + NO2 + 2 H2O → 5 N2 + 4 OH
N3 + 7 NO2 + 4 H2O → 10 NO + 8 OH

Applications

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In 2005, about 251 tons of azide-containing compounds were annually produced in the world, the main product being sodium azide.[7]

Primary explosives and propellants

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Sodium azide NaN3 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 NaN3 → 2 Na + 3 N2

Heavy metal azides, such as lead azide, Pb(N3)2, are shock-sensitive detonators which violently decompose to the corresponding metal and nitrogen, for example:[8]

Pb(N3)2 → Pb + 3 N2

Silver azide AgN3 and barium azide Ba(N3)2 are used similarly.

Some organic azides are potential rocket propellants, an example being 2-dimethylaminoethylazide (DMAZ) (CH3)2NCH2CH2N3.

Microbial inhibitor and undesirable side effects

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Sodium azide is commonly used in the laboratory as a bacteriostatic agent to avoid microbial proliferation in abiotic control experiments in which it is important to avoid microbial activity. However, it has the disadvantage to be prone to trigger unexpected and undesirable side reactions that can jeopardize the experimental results. Indeed, the azide anion is a nucleophile and a redox-active species. Being prone to disproportionation, it can behave both as an oxidizing and as a reducing agent. Therefore, it is susceptible to interfere in an unpredictable way with many substances.[9][10][11] For example, the azide anion can oxidize pyrite (FeS2) with the formation of thiosulfate (S2O2−3), or reduce quinone into hydroquinone.[12] It can also reduce nitrite NO2 into nitrous oxide N2O, and Fe2+ into Fe0 (zerovalent iron, ZVI).[12] Azide can also enhance the N2O emission in soil. A proposed explanation is the stimulation of the denitrification processes because of the azide’s role in the synthesis of denitrifying enzymes.[13] Moreover, azide also affects the absorbance and fluorescence optical properties of the dissolved organic matter (DOM) from soils.[14] Many other interferences are reported in the literature for biochemical and biological analyses and they should be systematically identified and first rigorously tested in the laboratory before to use azide as microbial inhibitor for a given application.

Other uses

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The azide functional group is commonly used[how?] in click chemistry.[clarification needed][citation needed]

Safety

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Azides are explosophores[9][15][16] and also respiratory poisons.[9] Sodium azide is as toxic as sodium cyanide (with an oral LD50 of 27 mg/kg in rats) and can be absorbed through the skin. When present in the air of a laboratory, it can also cause irritations such as nasal stuffiness, or even suffocation and death at elevated concentrations.[17]

Heavy metal azides, such as lead azide (Pb(N3)2) are primary high explosives detonable when heated or shaken. Heavy-metal azides are formed when solutions of sodium azide or HN3 vapors come into contact with heavy metals (Pb, Hg…) 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.[9]

See also

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References

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  1. ^ a b c 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.
  2. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 433. ISBN 978-0-08-037941-8.
  3. ^ 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.
  4. ^ Dönges, E. (1963). "Alkali Metals". In Brauer, G. (ed.). Handbook of Preparative Inorganic Chemistry. Vol. 1 (2nd ed.). NY: Academic Press. p. 475.
  5. ^ 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.
  6. ^ 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.{{cite book}}: CS1 maint: multiple names: authors list (link)
  7. ^ a b 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.
  8. ^ Shriver; Atkins. Inorganic Chemistry (5th ed.). New York: W. H. Freeman and Company. p. 382.
  9. ^ a b c d Rozycki, Michael; Bartha, Richard (1981). "Problems associated with the use of azide as an inhibitor of microbial activity in soil". Applied and Environmental Microbiology. 41 (3): 833–836. doi:10.1128/aem.41.3.833-836.1981. ISSN 0099-2240. PMC 243784. PMID 16345743.
  10. ^ Lindner, Pinhas; Shomer, Ilan (1984). "Interference of azide in assays of carbohydrates". Food Chemistry. 14 (2): 141–153. doi:10.1016/0308-8146(84)90053-0. ISSN 0308-8146.
  11. ^ Goel, Ramesh K; Cooper, Adrienne T; Flora, Joseph R.V (2003-09-01). "Sodium azide interference in chemical and biological testing". Journal of Environmental Engineering and Science. 2 (5): 407–411. doi:10.1139/s03-043. ISSN 1496-2551.
  12. ^ a b Hendrix, Katrien; Bleyen, Nele; Mennecart, Thierry; Bruggeman, Christophe; Valcke, Elie (2019). "Sodium azide used as microbial inhibitor caused unwanted by-products in anaerobic geochemical studies". Applied Geochemistry. 107: 120–130. doi:10.1016/j.apgeochem.2019.05.014. ISSN 0883-2927.
  13. ^ Aulakh, M. S.; Rennie, D. A. (1985-02-01). "Azide effects upon N2O emission and transformations of N in soils". Canadian Journal of Soil Science. 65 (1): 205–212. doi:10.4141/cjss85-021. ISSN 0008-4271.
  14. ^ Retelletti Brogi, Simona; Derrien, Morgane; Hur, Jin (2019). "In-depth assessment of the effect of sodium azide on the optical properties of dissolved organic matter". Journal of Fluorescence. 29 (4): 877–885. doi:10.1007/s10895-019-02398-w. ISSN 1053-0509.
  15. ^ Treitler, Daniel S.; Leung, Simon (2 September 2022). "How Dangerous Is Too Dangerous? A Perspective on Azide Chemistry". The Journal of Organic Chemistry. 87 (17): 11293–11295. doi:10.1021/acs.joc.2c01402. ISSN 0022-3263. PMID 36052475. S2CID 252009657. Retrieved 18 September 2022.
  16. ^ Mandler, Michael D.; Degnan, Andrew P.; Zhang, Shasha; Aulakh, Darpandeep; Georges, Ketleine; Sandhu, Bhupinder; Sarjeant, Amy; Zhu, Yeheng; Traeger, Sarah C.; Cheng, Peter T.; Ellsworth, Bruce A.; Regueiro-Ren, Alicia (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. S2CID 240154010.
  17. ^ Haas, Jonathan M.; Marsh, William W. (May 1970). "Sodium azide: A potential hazard when used to eliminate interferences in the iodometric determination of sulfur". American Industrial Hygiene Association Journal. 31 (3): 318–321. doi:10.1080/0002889708506248. ISSN 0002-8894.
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