Azide: Difference between revisions
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{{For|organic azides|organic azide}} | {{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> | 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 |bibcode=2005ACIE...44.5188B }}</ref> | ||
== Preparation == | == Preparation == | ||
| Line 10: | Line 10: | ||
:{{chem2|N2O + 2 NaNH2 → [[Sodium azide|NaN3]] + [[Sodium hydroxide|NaOH]] + [[Ammonia|NH3]]}} | :{{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]]. | 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 |bibcode=2014ACIE...5313695M }}</ref> Some azides are produced by treating the [[carbonate]] [[Salt (chemistry)|salt]]s with [[hydrazoic acid]]. | ||
== Bonding == | == Bonding == | ||
Azide 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-}}. | 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 == | == Reactions == | ||
| Line 19: | Line 19: | ||
:{{chem2|2 MN3}} {{overset|heat|→}} {{chem2|2 M + 3 N2}} | :{{chem2|2 MN3}} {{overset|heat|→}} {{chem2|2 M + 3 N2}} | ||
[[Protonation]] of azide salts gives toxic [[hydrazoic acid]] in the presence of [[strong acid]]s: | [[Protonation]] of azide salts gives toxic and explosive [[hydrazoic acid]] in the presence of [[strong acid]]s: | ||
:{{chem2|H+ + N3− → HN3}} | :{{chem2|H+ + N3− → HN3}} | ||
| Line 45: | Line 45: | ||
:{{chem2|N3- + 7 NO2- + 4 H2O → 10 NO + 8 OH-}} | :{{chem2|N3- + 7 NO2- + 4 H2O → 10 NO + 8 OH-}} | ||
Azide ( | (The parenthetical notation below marks the [[oxidation state]] of the nitrogen in each species.) | ||
Azide (−{{sfrac|1|3}}) (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 == | == Applications == | ||
| Line 64: | Line 66: | ||
=== Microbial inhibitor and undesirable side effects === | === 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. | 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 | bibcode=1981ApEnM..41..833R }}</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 | bibcode=2003JEES....2..407G }}</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 | bibcode=2019ApGC..107..120H }}</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 | bibcode=1985CaJSS..65..205A }}</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 | pmid=31218596 }}</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 === | === 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= | 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 V), and is even a stronger [[Reducing agent|reductant]] than lithium (''E''°<sub>red</sub> = −3.04 V), dry solid [[sodium azide]] can be added to molten metallic sodium (''E''°<sub>red</sub> = −2.71 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 hydrazoic acid, the [[Protonation|protonated]] form of the azide anion, has a very low reduction potential (''E''°<sub>red</sub> = −3.09 V), and is even a stronger [[Reducing agent|reductant]] than lithium (''E''°<sub>red</sub> = −3.04 V), dry solid [[sodium azide]] can be added to molten metallic sodium (''E''°<sub>red</sub> = −2.71 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}}. | ||
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== Safety == | == 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 as toxic as [[sodium cyanide]] (NaCN) (with an oral {{LD50}} of 27 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> | 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 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 |pmid=5428568 |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" /> | [[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" /> | ||
Latest revision as of 14:21, 7 December 2025
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In chemistry, azide (Template:IPAc-en, Script error: No such module "Respell".) is a linear, polyatomic anion with the formula Template:Chem2 and structure Template:Chem2. It is the conjugate base of hydrazoic acid Template:Chem2. Organic azides are organic compounds with the formula Template:Chem2, 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, Template:Chem2 with sodium amide Template:Chem2 in liquid ammonia as solvent:[2]
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 has a linear structure and is isoelectronic with carbon dioxide Template:Chem2, cyanate Template:Chem2, nitrous oxide Template:Chem2, nitronium ion Template:Chem2, molecular beryllium fluoride Template:Chem2 and cyanogen fluoride FCN. Per valence bond theory, azide can be described by several resonance structures; an important one being Template:Chem2. 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|Template:Chem2]] (275 °C), [[Potassium azide|Template:Chem2]] (355 °C), [[Rubidium azide|Template:Chem2]] (395 °C), and [[Caesium azide|Template:Chem2]] (390 °C). This method is used to produce ultrapure alkali metals:[4]
Protonation of azide salts gives toxic and explosive hydrazoic acid in the presence of strong acids:
Azide as a ligand forms numerous transition metal azide complexes. Some such compounds are shock sensitive.
Many inorganic covalent azides (e.g., fluorine azide, chlorine azide, bromine azide, iodine azide, silicon tetraazide) 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 [[nitrogen|Template:Chem2]], generating a metal complex in unusual oxidation states (see high-valent iron).
Redox behaviour and trend to disproportionation
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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 Template:Chem2 (or the azide ion) surrounded by two much more stable species, the ammonium ion Template:Chem2 on the left and the molecular nitrogen Template:Chem2 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.
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 (Template:Chem2) converge to a same one (respectively Template:Chem2) and is favored when the solution is acidified. This is a method of destroying residual azides, prior to disposal.[6] In the process, nitrogen gas (Template:Chem2) and nitrogen oxides (Template:Chem2 and NO) are formed:
(The parenthetical notation below marks the oxidation state of the nitrogen in each species.)
Azide (−Template:Sfrac) (the reductant, electron donor) is oxidized in Template:Chem2 (0), nitrous oxide (Template:Chem2) (+1), or nitric oxide (NO) (+2) while nitrite (+3) (the oxidant, electron acceptor) is simultaneously 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: Template:Chem2, 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.[7]
Primary explosives and propellants
Sodium azide Template:Chem2 is the propellant in automobile airbags. It decomposes on heating to give nitrogen gas, which is used to quickly expand the air bag:[7]
Heavy metal azides, such as lead azide, Template:Chem2, are shock-sensitive detonators which violently decompose to the corresponding metal and nitrogen, for example:[8]
Silver azide Template:Chem2 and barium azide Template:Chem2 are used similarly.
Some organic azides are potential rocket propellants, an example being 2-dimethylaminoethylazide (DMAZ) Template:Chem2.
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-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 (Template:Chem2) with the formation of thiosulfate (Template:Chem2), or reduce quinone into hydroquinone.[12] It can also reduce nitrite Template:Chem2 into nitrous oxide Template:Chem2, and Template:Chem2 into Template:Chem2 (zerovalent iron, ZVI).[12] Azide can also enhance the Template: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.
Purification of molten sodium
Sodium azide Template:Chem2 is used to purify metallic sodium in laboratories handling molten sodium used as a coolant for fast-neutron reactors.[15]
As hydrazoic acid, the protonated form of the azide anion, has a very low reduction potential (E°red = −3.09 V), and is even a stronger reductant than lithium (E°red = −3.04 V), dry solid sodium azide can be added to molten metallic sodium (E°red = −2.71 V) under strict anoxic conditions (e.g., in a special anaerobic glovebox with very low residual Template:O2 (< 1 ppm vol.) to reduce Template:Chem2 impurities still present into the sodium bath. The reaction residue is only gaseous Template:Chem2.
As E°ox = −E°red, it gives the following series of oxidation reactions when the redox couples are presented as reductants:
- Template:Chem2 (E°ox = +3.09 V)
- Template:Chem2 (E°ox = +3.04 V)
- Template:Chem2 (E°ox = +2.71 V)
Click chemistry
Template:Main article The azide functional group is commonly utilized in click chemistry through copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions, where copper(I) catalyzes the cycloaddition of an organoazide to a terminal alkyne, forming a triazole.[16][17][18]
Other uses
A very damaging and illegal usage of sodium azide is its diversion by 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 explosophores[9][19][20] and respiratory poisons.[9][21] Sodium azide (Template:Chem2) is nearly as toxic as sodium cyanide (NaCN) (with an oral LD50 of 27 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 (Template:Chem2), 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 suffocation and death at elevated concentrations.[22]
Heavy metal azides, such as lead azide (Template:Chem2) are primary high explosives detonable when heated or shaken. Heavy-metal azides are formed when solutions of sodium azide or Template:Chem2 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
References
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External links
Template:Sister project Template:Sister project
Template:Nitrogen compounds Template:Azides Template:Authority control