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{{Short description|Anion and chemical group (–N3)}}
[[File:Azid-Ion.svg|thumb|The azide anion]]
{{For|organic azides|organic azide}}

In [[chemistry]], '''azide''' ({{IPAc-en|ˈ|eɪ|z|aɪ|d}}, {{Respell|AY|zyd}}) is a [[Linear molecular geometry|linear]], [[polyatomic anion]] with the [[Chemical formula|formula]] {{chem2|N3-|auto=1}} and [[Chemical structure|structure]] {{chem2|-N\dN+\dN-}}. It is the [[conjugate base]] of [[hydrazoic acid]] {{chem2|HN3}}. [[Organic azide]]s are [[organic compound]]s with the formula {{chem2|RN3}}, containing the azide [[functional group]].<ref name = braese/> The dominant application of azides is as a [[propellant]] in [[air bag]]s.<ref name = braese>{{cite journal |author1=S. Bräse |author2=C. Gil |author3=K. Knepper |author4=V. Zimmermann | title = Organic Azides: An Exploding Diversity of a Unique Class of Compounds | journal = [[Angewandte Chemie International Edition]] | volume = 44 | issue = 33 | pages = 5188–5240 | doi = 10.1002/anie.200400657 | year = 2005 | pmid = 16100733}}</ref>

== Preparation ==
[[Sodium azide]] is made industrially by the reaction of [[nitrous oxide]], {{chem2|N2O}} with [[sodium amide]] {{chem2|NaNH2}} in [[liquid ammonia]] as [[solvent]]:<ref>{{Greenwood&Earnshaw2nd|page=433}}</ref>

:{{chem2|N2O + 2 NaNH2 → [[Sodium azide|NaN3]] + [[Sodium hydroxide|NaOH]] + [[Ammonia|NH3]]}}

Many inorganic azides can be prepared directly or indirectly from sodium azide. For example, [[lead azide]], used in [[detonator]]s, may be prepared from the [[Salt metathesis reaction|metathesis reaction]] between [[lead nitrate]] and sodium azide. An alternative route is direct reaction of the metal with [[silver azide]] dissolved in [[liquid ammonia]].<ref>{{cite journal | title=A New Route to Metal Azides |journal=Angewandte Chemie |volume=53 |issue=50 |pages=13695–13697 | doi=10.1002/anie.201404561|year=2014 |last1=Müller |first1=Thomas G. |last2=Karau |first2=Friedrich |last3=Schnick |first3=Wolfgang |last4=Kraus |first4=Florian |pmid=24924913 }}</ref> Some azides are produced by treating the [[carbonate]] [[Salt (chemistry)|salt]]s with [[hydrazoic acid]].

== Bonding ==
Azide has a linear structure and is [[isoelectronic]] with [[carbon dioxide]] {{chem2|CO2}}, [[cyanate]] {{chem2|OCN−}}, [[nitrous oxide]] {{chem2|N2O}}, [[nitronium ion]] {{chem2|NO2+}}, molecular [[beryllium fluoride]] {{chem2|BeF2}} and [[cyanogen fluoride]] FCN. Per [[valence bond theory]], azide can be described by several [[resonance structure]]s; an important one being {{chem2|N-\dN+\dN-}}. The analogous neutral [[trinitrogen]] molecule can also have a linear structure, but also a cyclic [[isomer]] is known.

== Reactions ==
Azide salts can decompose with release of [[nitrogen gas]]. The decomposition temperatures of the [[alkali metal]] azides are: [[Sodium azide|{{chem2|NaN3}}]] (275&nbsp;°C), [[Potassium azide|{{chem2|KN3}}]] (355&nbsp;°C), [[Rubidium azide|{{chem2|RbN3}}]] (395&nbsp;°C), and [[Caesium azide|{{chem2|CsN3}}]] (390&nbsp;°C). This method is used to produce ultrapure alkali metals:<ref>{{cite book |first=E. |last=Dönges |chapter=Alkali Metals |title=Handbook of Preparative Inorganic Chemistry |edition=2nd |editor-first=G. |editor-last=Brauer |publisher=Academic Press |year=1963 |location=NY |volume=1 |page=475}}</ref>
:{{chem2|2 MN3}} {{overset|heat|→}} {{chem2|2 M + 3 N2}}

[[Protonation]] of azide salts gives toxic and explosive [[hydrazoic acid]] in the presence of [[strong acid]]s:

:{{chem2|H+ + N3− → HN3}}

Azide as a [[ligand]] forms numerous [[transition metal azide complex]]es. Some such compounds are [[Explosive|shock sensitive]].

Many [[inorganic]] [[covalent]] azides (e.g., [[fluorine azide]], [[chlorine azide]], [[bromine azide]], [[iodine azide]], [[silicon tetraazide]]) have been described.<ref>{{cite journal |author1=I. C. Tornieporth-Oetting |author2=T. M. Klapötke |name-list-style=amp | title = Covalent Inorganic Azides | journal = [[Angewandte Chemie International Edition in English]] | volume = 34 | issue = 5 | pages = 511–520 | doi = 10.1002/anie.199505111 | year = 1995}}</ref>

The azide anion behaves as a [[nucleophile]]; it undergoes [[nucleophilic substitution]] for both [[aliphatic]] and [[aromatic]] systems. It reacts with [[epoxide]]s, causing a ring-opening; it undergoes [[Michael-like]] [[conjugate addition]] to 1,4-[[Saturated and unsaturated compounds|unsaturated]] [[carbonyl compounds]].<ref name = braese/>

Azides can be used as precursors of the [[metal nitrido complex]]es by being induced to release [[nitrogen|{{chem2|N2}}]], generating a [[metal complex]] in unusual [[oxidation states]] (see ''[[high-valent iron]]'').

=== Redox behaviour and trend to disproportionation ===
{{Main articles|Disproportionation|Comproportionation|Frost diagram}}
[[File:Nitrogen frost diagramm.png|thumb|300px|[[Frost diagram]] for nitrogen species at [[pH]] = 0]]
Azides have an ambivalent [[redox]] behavior: they are both [[Redox|oxidizing]] and [[Redox|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]] {{Chem2|HN3}} (or the azide ion) surrounded by two much more stable species, the [[ammonium]] [[ion]] {{Chem2|NH4+}} on the left and the molecular [[nitrogen]] {{Chem2|N2}} on the right. As seen on the Frost diagram the disproportionation reaction lowers ∆G, the [[Gibbs free energy]] of the system {{Nowrap|(−∆G/F {{=}} zE}}, where F is the [[Faraday constant]], z the number of [[electron]]s exchanged in the redox reaction, and E the [[standard electrode potential]]). By minimizing the energy in the system, the disproportionation reaction increases its [[Thermodynamics|thermodynamical]] stability.

=== Destruction by oxidation by nitrite ===
Azides decompose with nitrite compounds such as [[sodium nitrite]]. Each elementary [[redox]] reaction is also a [[comproportionation]] reaction because two different N-species ({{Chem2|N3- and NO2-}}) converge to a same one (respectively {{Chem2|N2, N2O and NO}}) and is favored when the solution is acidified. This is a method of destroying residual azides, prior to disposal.<ref>{{cite book | title = Prudent practices in the laboratory: handling and disposal of chemicals | year = 1995 | publisher = [[National Academy Press]] | location = Washington, D.C. | isbn = 0-309-05229-7 | url = http://books.nap.edu/openbook.php?record_id=4911&page=165 | author = 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}}</ref> In the process, nitrogen gas ({{chem2|N2}}) and nitrogen oxides ({{chem2|N2O}} and NO) are formed:

:{{chem2|3 N3- + NO2- + 2 H2O → 5 N2 + 4 OH-}}

:{{chem2|2 N3- + 4 NO2- + 3 H2O → 5 N2O + 6 OH-}}

:{{chem2|N3- + 7 NO2- + 4 H2O → 10 NO + 8 OH-}}

Azide (<em>−⅓</em>) (the [[Reducing agent|reductant]], [[electron donor]]) is [[Redox|oxidized]] in {{Chem2|N2}} (0), [[nitrous oxide]] ({{Chem2|N2O}}) (+1), or [[nitric oxide]] (NO) (+2) while [[nitrite]] (+3) (the [[Oxidizing agent|oxidant]], [[electron acceptor]]) is simultaneously [[Redox|reduced]] to the same corresponding species in each elementary redox reaction considered here above. The respective stability of the reaction products of these three [[comproportionation]] redox reactions is in the following order: {{Chem2|N2 > N2O > NO}}, as can be verified in the Frost diagram for nitrogen.

== Applications ==
In 2005, about 251 tons of azide-containing compounds were annually produced in the world, the main product being sodium azide.<ref name=Ullmann>{{cite book |first1=Horst H. |last1=Jobelius |first2=Hans-Dieter |last2=Scharff |chapter=Hydrazoic Acid and Azides |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2005 |publisher=Wiley-VCH |location=Weinheim |doi=10.1002/14356007.a13_193|isbn=3527306730 }}</ref>

=== Primary explosives and propellants===
[[Sodium azide]] {{chem2|NaN3}} is the propellant in automobile [[airbag]]s. It decomposes on heating to give nitrogen gas, which is used to quickly expand the air bag:<ref name=Ullmann/>

:{{chem2|2 NaN3 → 2 Na + 3 N2}}

Heavy metal azides, such as [[lead azide]], {{chem2|Pb(N3)2}}, are shock-sensitive [[detonator]]s which violently decompose to the corresponding metal and nitrogen, for example:<ref>{{cite book |last1=Shriver |last2=Atkins |title=Inorganic Chemistry |edition=5th |publisher= W. H. Freeman and Company |location=New York |page=382}}</ref>

:{{chem2|Pb(N3)2 → Pb + 3 N2}}

[[Silver azide]] {{chem2|AgN3}} and [[barium azide]] {{chem2|Ba(N3)2}} are used similarly.

Some organic azides are potential [[Rocket propellant|rocket propellants]], an example being [[2-Dimethylaminoethylazide|2-dimethylaminoethylazide]] (DMAZ) {{chem2|(CH3)2NCH2CH2N3}}.

=== Microbial inhibitor and undesirable side effects ===
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|redox-active]] species. Being prone to [[disproportionation]], it can behave both as an [[oxidizing agent| oxidizing]] and as a [[reducing agent]]. Therefore, it is susceptible to interfere in an unpredictable way with many substances.<ref name="Rozycki1981">{{cite journal | last1=Rozycki | first1=Michael | last2=Bartha | first2=Richard | date=1981 | title=Problems associated with the use of azide as an inhibitor of microbial activity in soil | journal=Applied and Environmental Microbiology | volume=41 | issue=3 | pages=833–836 | issn=0099-2240 | pmid=16345743 | pmc=243784 | doi=10.1128/aem.41.3.833-836.1981}}</ref><ref name="Lindner1984">{{cite journal | last1=Lindner | first1=Pinhas | last2=Shomer | first2=Ilan | year=1984 | title=Interference of azide in assays of carbohydrates | journal=Food Chemistry | volume=14 | issue=2 | pages=141–153 | issn=0308-8146 | doi=10.1016/0308-8146(84)90053-0}}</ref><ref name="Goel2003">{{cite journal | last1=Goel | first1=Ramesh K | last2=Cooper | first2=Adrienne T | last3=Flora | first3=Joseph R.V | date=2003-09-01 | title=Sodium azide interference in chemical and biological testing | journal=Journal of Environmental Engineering and Science | volume=2 | issue=5 | pages=407–411 | issn=1496-2551 | doi=10.1139/s03-043}}</ref> For example, the azide anion can [[Redox|oxidize]] [[pyrite]] ({{Chem2|FeS2}}) with the formation of [[thiosulfate]] ({{Chem2|S2O3(2-)}}), or [[Redox|reduce]] [[quinone]] into [[hydroquinone]].<ref name="Hendrix2019">{{cite journal | last1=Hendrix | first1=Katrien | last2=Bleyen | first2=Nele | last3=Mennecart | first3=Thierry | last4=Bruggeman | first4=Christophe | last5=Valcke | first5=Elie | title=Sodium azide used as microbial inhibitor caused unwanted by-products in anaerobic geochemical studies | journal=Applied Geochemistry | volume=107 | year=2019 | issn=0883-2927 | doi=10.1016/j.apgeochem.2019.05.014 | pages=120–130}}</ref> It can also reduce [[nitrite]] {{Chem2|NO2-}} into [[nitrous oxide]] {{Chem2|N2O}}, and {{Chem2|Fe(2+)}} into {{Chem2|Fe^{0}|}} ([[zerovalent iron]], ZVI).<ref name="Hendrix2019" /> 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.<ref name="Aulakh1985">{{cite journal | last1=Aulakh | first1=M. S. | last2=Rennie | first2=D. A. | date=1985-02-01 | title=Azide effects upon N<sub>2</sub>O emission and transformations of N in soils | journal=Canadian Journal of Soil Science | volume=65 | issue=1 | pages=205–212 | issn=0008-4271 | doi=10.4141/cjss85-021}}</ref> Moreover, azide also affects the [[absorbance]] and [[fluorescence]] optical properties of the [[Dissolved organic carbon|dissolved organic matter]] (DOM) from [[soil]]s.<ref name="RetellettiBrogi2019">{{cite journal | last1=Retelletti Brogi | first1=Simona | last2=Derrien | first2=Morgane | last3=Hur | first3=Jin | date=2019 | title=In-depth assessment of the effect of sodium azide on the optical properties of dissolved organic matter | journal=[[Journal of Fluorescence]] | volume=29 | issue=4 | pages=877–885 | issn=1053-0509 | doi=10.1007/s10895-019-02398-w}}</ref> Many other interferences are reported in the literature for [[Biochemistry|biochemical]] and [[Biology|biological]] analyses and they should be systematically identified and first rigorously tested in the laboratory before to use azide as [[bacteriostatic|microbial inhibitor]] for a given application. 

=== Purification of molten sodium ===
Sodium azide {{Chem2|NaN3}} is used to purify metallic sodium in laboratories handling molten sodium used as a coolant for [[fast-neutron reactor]]s.<ref name="Weber1951">{{Cite journal | last1=Weber | first1=C. E. | date=July 1948 – January 1951| title=Problems in the use of molten sodium as transfer fluid. OSTI declassified document | journal=Journal of Metallurgy and Ceramics | issue= 1 – 6 | page=291 | url=https://www.osti.gov/servlets/purl/4302453#page=202}}</ref>

As hydrazoic acid, the [[Protonation|protonated]] form of the azide anion, has a very low reduction potential (''E''°<sub>red</sub> = −3.09&nbsp;V), and is even a stronger [[Reducing agent|reductant]] than lithium (''E''°<sub>red</sub> = −3.04&nbsp;V), dry solid [[sodium azide]] can be added to molten metallic sodium (''E''°<sub>red</sub> = −2.71&nbsp;V) under strict anoxic conditions (''e.g.'', in a special anaerobic glovebox with very low residual {{O2}} {{Nowrap|(< 1 ppm vol.)}} to reduce {{Chem2|Na+}} impurities still present into the sodium bath. The reaction residue is only gaseous {{chem2|N2}}.

As ''E''°<sub>ox</sub> = −''E''°<sub>red</sub>, it gives the following series of oxidation reactions when the redox couples are presented as reductants: 
*{{Chem2|2 HN3 ⇌ 3 N2(g) + 2 H+ + 2 e-}} (''E''°<sub>ox</sub> = +3.09&nbsp;V)
*{{Chem2|Li ⇌ Li+ + e-}} (''E''°<sub>ox</sub> = +3.04&nbsp;V)
*{{Chem2|Na ⇌ Na+ + e-}} (''E''°<sub>ox</sub> = +2.71&nbsp;V)

=== Click chemistry ===
{{Main article|Click chemistry|Azide-alkyne Huisgen cycloaddition}}
The azide [[functional group]] is commonly utilized in [[click chemistry]] through [[Copper#Compounds|copper(I)]]-[[Catalysis|catalyzed]] azide-[[alkyne]] [[cycloaddition]] ([[CuAAC]]) reactions, where copper(I) catalyzes the cycloaddition of an organoazide to a terminal alkyne, forming a [[triazole]].<ref>{{cite journal| journal = Proceedings of the Chemical Society of London| page = 357| year= 1961| title = Centenary Lecture – 1,3-Dipolar Cycloadditions| author = Huisgen, R. | doi = 10.1039/PS9610000357}}</ref><ref>{{cite journal |author1=H. C. Kolb |author2=M. G. Finn |author3=K. B. Sharpless | title = Click Chemistry: Diverse Chemical Function from a Few Good Reactions | year = 2001 | journal = [[Angewandte Chemie International Edition]] | volume = 40 | issue = 11 | pages = 2004–2021 | doi = 10.1002/1521-3773(20010601)40:11<2004::AID-ANIE2004>3.0.CO;2-5 | pmid=11433435| doi-access = free }}</ref><ref>{{cite journal|last=Kolb|first=H.C.|author2=Sharpless, B.K.|title=The growing impact of click chemistry on drug discovery|year=2003|volume=8|issue=24|pages=1128–1137|doi=10.1016/S1359-6446(03)02933-7|pmid=14678739|journal=Drug Discov Today|doi-access=free}}</ref>

=== Other uses ===
A very damaging and illegal usage of sodium azide is its diversion by [[Poaching|poachers]] as a substitute of [[sodium cyanide]] to poison some animal species by blocking the [[electron transport chain]] in the [[cellular respiration]] process.

== Safety ==
Azides are [[explosophore]]s<ref name="Rozycki1981" /><ref>{{cite journal |last1=Treitler |first1=Daniel S. |last2=Leung |first2=Simon |title=How Dangerous is too Dangerous? A Perspective on Azide Chemistry |journal=[[The Journal of Organic Chemistry]] |date=2 September 2022 |volume=87 |issue=17 |pages=11293–11295 |doi=10.1021/acs.joc.2c01402 |pmid=36052475 |s2cid=252009657 |url=https://pubs.acs.org/doi/10.1021/acs.joc.2c01402 |access-date=18 September 2022 |language=en |issn=0022-3263|url-access=subscription }}</ref><ref>{{cite journal |last1=Mandler |first1=Michael D. |last2=Degnan |first2=Andrew P. |last3=Zhang |first3=Shasha |last4=Aulakh |first4=Darpandeep |last5=Georges |first5=Ketleine |last6=Sandhu |first6=Bhupinder |last7=Sarjeant |first7=Amy |last8=Zhu |first8=Yeheng |last9=Traeger |first9=Sarah C. |last10=Cheng |first10=Peter T. |last11=Ellsworth |first11=Bruce A. |last12=Regueiro-Ren |first12=Alicia |title=Structural and Thermal Characterization of Halogenated Azidopyridines: Under-Reported Synthons for Medicinal Chemistry |journal=Organic Letters |date=28 January 2022 |volume=24 |issue=3 |pages=799–803 |doi=10.1021/acs.orglett.1c03201|pmid=34714083 |s2cid=240154010 }}</ref> and respiratory poisons.<ref name="Rozycki1981" /><ref name="Tat2021">{{cite journal | last1=Tat | first1=John | last2=Heskett | first2=Karen | last3=Satomi | first3=Shiho | last4=Pilz | first4=Renate B. | last5=Golomb | first5=Beatrice A. | last6=Boss | first6=Gerry R. | title=Sodium azide poisoning: A narrative review | journal=Clinical Toxicology | volume=59 | issue=8 | date=2021-08-03 | issn=1556-3650 | pmid=34128439 | pmc=8349855 | doi=10.1080/15563650.2021.1906888 | pages=683–697}}</ref> [[Sodium azide]] ({{Chem2|NaN3}}) is nearly as toxic as [[sodium cyanide]] (NaCN) (with an oral {{LD50}} of 27&nbsp;mg/kg in rats) and can be absorbed through the skin. When sodium azide enters in contact with an acid, it produces volatile [[hydrazoic acid]] ({{Chem2|HN3}}), as toxic and volatile as [[hydrogen cyanide]] (HCN). When accidentally present in the air of a laboratory at low concentration, it can cause irritations such as nasal stuffiness, or [[Asphyxia|suffocation]] and death at elevated concentrations.<ref name="Haas1970">{{cite journal |last1=Haas |first1=Jonathan M. |last2=Marsh |first2=William W. |date=May 1970 |title=Sodium azide: A potential hazard when used to eliminate interferences in the iodometric determination of sulfur |journal=American Industrial Hygiene Association Journal |volume=31 |issue=3 |pages=318–321 |doi=10.1080/0002889708506248 |url=https://www.tandfonline.com/doi/abs/10.1080/0002889708506248 |language=en |issn=0002-8894|url-access=subscription }}</ref>

[[Heavy metals|Heavy metal]] azides, such as [[lead azide]] ({{chem2|Pb(N3)2}}) are [[primary explosives|primary]] [[high explosive]]s [[detonation|detonable]] when heated or shaken. Heavy-metal azides are formed when solutions of sodium azide or {{chem2|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 evaporator]]s, [[freeze drying|freezedrying]] equipment, cooling traps, water baths, waste pipes), and thus lead to violent explosions.<ref name="Rozycki1981" />

== See also ==
* [[Main group azido compounds]]
* [[Pentazenium]]
* [[Pentazolate]] (''cyclo''-{{chem2|N5−}})

== References ==

{{Reflist|2}}

== External links ==
{{Wiktionary|azide|azido-}}
{{Commons category|Azides}}
* [https://www.organic-chemistry.org/synthesis/C1N/azides/index.shtm Synthesis of organic azides], recent methods
* [http://www.ehs.ucsb.edu/units/labsfty/labrsc/factsheets/Azides_FS26.pdf Synthesizing, purifying, and handling organic azides]

{{Nitrogen compounds}}
{{Azides}}
{{Authority control}}

[[Category:Azides]]