Editing Dinitrogen tetroxide

{{chembox
| Verifiedfields = changed
| Watchedfields  = changed
| verifiedrevid  = 477162897
| Name           = Dinitrogen tetroxide
| ImageFile      = 
| ImageFileL1    = Dinitrogen tetroxide.svg
| ImageClassL1 = skin-invert-image
| ImageNameL1    = Full structural formula
| ImageFileR1    = Dinitrogen-tetroxide-3D-vdW.png
| ImageClassR1 = bg-transparent
| ImageNameR1    = Space-filling model
| ImageFile2     = Nitrogen dioxide at different temperatures.jpg
| ImageSize2     = 240
| ImageCaption2  = [[Nitrogen dioxide]] at −196&nbsp;°C, 0&nbsp;°C, 23&nbsp;°C, 35&nbsp;°C, and 50&nbsp;°C. ({{chem|NO|2}}) converts to the colorless dinitrogen tetroxide ({{chem|N|2|O|4}}) at low temperatures, and reverts to {{chem|NO|2}} at higher temperatures.
| ImageFile2_Ref = {{chemboximage|correct|??}}
| ImageName2     = Nitrogen dioxide at different temperatures
| IUPACName      = Dinitrogen tetroxide
| OtherNames     = 
| SystematicName = 
| Section1       = {{Chembox Identifiers
| CASNo = 10544-72-6
| CASNo_Ref = {{cascite|correct|CAS}}
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 23681
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 29803
| Gmelin = 2249
| PubChem = 25352
| EINECS = 234-126-4
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = M9APC3P75A
| UNNumber = 1067
| RTECS = QW9800000
| SMILES = [O-][N+](=O)[N+]([O-])=O
| InChI = 1/N2O4/c3-1(4)2(5)6
| InChIKey = WFPZPJSADLPSON-UHFFFAOYAS
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/N2O4/c3-1(4)2(5)6
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = WFPZPJSADLPSON-UHFFFAOYSA-N
  }}
| Section2       = {{Chembox Properties
| N=2 | O=4
| Appearance = White solid, colorless liquid, orange gas
| Density = 1.44246{{nbsp}}g/cm<sup>3</sup> (liquid, 21&nbsp;°C)
| Solubility = Reacts to form nitrous and nitric acids
| MeltingPtC = −11.2
| MeltingPt_notes = and decomposes to NO<sub>2</sub>
| BoilingPtC = 21.69
| VaporPressure = 96{{nbsp}}kPa (20{{nbsp}}°C)<ref>[https://www.ilo.org/dyn/icsc/showcard.display?p_lang=en&p_card_id=0930&p_version=2 ''International Chemical Safety Card''] https://www.ilo.org/dyn/icsc/showcard.display?p_lang=en&p_card_id=0930&p_version=2</ref>
| RefractIndex = 1.00112
| MagSus = −23.0·10<sup>−6</sup>{{nbsp}}cm<sup>3</sup>/mol
  }}
| Section3       = {{Chembox Structure
| MolShape = Planar, ''D''<sub>2h</sub>
| Dipole = small, non-zero
  }}
| Section4       = {{Chembox Thermochemistry
| DeltaHf = +9.16{{nbsp}}kJ/mol<ref name=Atkins>P.W. Atkins and J. de Paula, ''Physical Chemistry'' (8th ed., W.H. Freeman, 2006) p.999</ref>
| Entropy = 304.29{{nbsp}}J/K⋅mol<ref name=Atkins/>
  }}
| Section5       = 
| Section6       = 
| Section7       = {{Chembox Hazards
| ExternalSDS = [https://www.airgas.com/msds/001041.pdf External SDS]
| GHSPictograms = {{GHS03}}{{GHS05}}{{GHS06}}{{GHS07}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|270|314|330|335|336}}
| PPhrases = {{P-phrases|220|244|260|261|264|271|280|284|301+330+331|303+361+353|304+340|305+351+338|310|312|320|321|363|370+376|403|403+233|405|410+403|501}}
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R = 0
| NFPA-S = OX
| NFPA_ref = <ref>{{cite web |url= https://cameochemicals.noaa.gov/chemical/4075 |title= Chemical Datasheet: Nitrogen tetroxide |work= [[CAMEO Chemicals]] [[National Oceanic and Atmospheric Administration|NOAA]] |access-date= 8 September 2020}}</ref><ref>{{cite web |url= https://pubchem.ncbi.nlm.nih.gov/compound/Dinitrogen-tetroxide#section=NFPA-Hazard-Classification |title= Compound Summary: Dinitrogen tetroxide |work= [[PubChem]] |access-date= 8 September 2020}}</ref>
| FlashPt = Non-flammable
| LD50 =
| PEL =
  }}
| Section8       = {{Chembox Related
| OtherFunction = {{ubl
 | [[Nitrous oxide]]
 | [[Nitric oxide]]
 | [[Dinitrogen trioxide]]
 | [[Nitrogen dioxide]]
 | [[Dinitrogen pentoxide]]
 }}
| OtherFunction_label = [[nitrogen]] [[oxide]]s
| OtherCompounds = {{ubl
| [[Phosphorus tetroxide]]
| [[Arsenic tetroxide]]
| [[Antimony tetroxide]]
}}
  }}
}}
'''Dinitrogen tetroxide''', commonly referred to as '''nitrogen tetroxide''' ('''NTO'''), and occasionally (usually among ex-USSR/Russian rocket engineers) as '''amyl''', is the [[chemical compound]] N<sub>2</sub>O<sub>4</sub>. It is a useful [[reagent]] in chemical synthesis. It forms an [[Chemical equilibrium|equilibrium mixture]] with [[nitrogen dioxide]]. Its molar mass is 92.011 g/mol.

Dinitrogen tetroxide is a powerful [[oxidizer]] that is [[hypergolic]] (spontaneously reacts) upon contact with various forms of [[hydrazine]], which has made the pair a common [[bipropellant]] for rockets.

==Structure and properties==
Dinitrogen tetroxide could be regarded as two [[nitro group]]s (-NO<sub>2</sub>) bonded together. It forms an [[Chemical equilibrium|equilibrium mixture]] with [[nitrogen dioxide]].<ref>{{Cite journal |doi = 10.1021/ic50008a020|title = Dimers of Nitrogen Dioxide. II. Structure and Bonding|journal = Inorganic Chemistry|volume = 2|issue = 4|pages = 747–752|year = 1963|last1 = Bent|first1 = Henry A.}}</ref>  The molecule is planar with an N-N bond distance of 1.78{{nbsp}}Å and N-O distances of 1.19{{nbsp}}Å. The N-N distance corresponds to a weak bond, since it is significantly longer than the average N-N single bond length of 1.45{{nbsp}}Å.<ref>{{cite book |last1 = Petrucci |first1 = Ralph H. |last2 = Harwood |first2 = William S. |last3 = Herring |first3 = F. Geoffrey |date=2002 |title = General chemistry: principles and modern applications |url = https://archive.org/details/generalchemistry00hill |url-access = registration |edition=8th |location=Upper Saddle River, N.J |publisher=Prentice Hall |isbn = 978-0-13-014329-7 |lccn=2001032331 |oclc=46872308 |page=[https://archive.org/details/generalchemistry00hill/page/420 420] }}</ref> This exceptionally weak σ bond (amounting to overlapping of the ''sp''<sup>2</sup> hybrid orbitals of the two NO<sub>2</sub> units<ref>{{Cite book|last=Rayner-canham|first=Geoff|url=https://www.worldcat.org/oclc/1026755795|title=Descriptive inorganic chemistry.|date=2013|isbn=978-1-319-15411-0|edition=6th|pages=400|oclc=1026755795}}</ref>) results from the simultaneous delocalization of the bonding electron pair across the whole N<sub>2</sub>O<sub>4</sub> molecule, and the considerable electrostatic repulsion of the doubly occupied molecular orbitals of each NO<sub>2</sub> unit.<ref>{{Cite journal|last1=Ahlrichs|first1=Reinhart|last2=Keil|first2=Frerich|date=1974-12-01|title=Structure and bonding in dinitrogen tetroxide (N2O4)|url=https://doi.org/10.1021/ja00832a002|journal=Journal of the American Chemical Society|volume=96|issue=25|pages=7615–7620|doi=10.1021/ja00832a002|issn=0002-7863|url-access=subscription}}</ref>

Unlike NO<sub>2</sub>, N<sub>2</sub>O<sub>4</sub> is [[diamagnetism|diamagnetic]] since it has no unpaired electrons.<ref name=HW>Holleman, A. F.; Wiberg, E. (2001) ''Inorganic Chemistry''. Academic Press: San Diego. {{ISBN|978-0-12-352651-9}}.</ref>  The liquid is also colorless but can appear as a brownish yellow liquid due to the presence of NO<sub>2</sub> according to the following equilibrium:<ref name=HW/>
: N<sub>2</sub>O<sub>4</sub> ⇌ 2 NO<sub>2</sub>{{Pad|2em}}({{Math|Δ''H'' {{=}} +57.23 kJ/mol}})

Higher temperatures push the equilibrium towards nitrogen dioxide.  Inevitably, some dinitrogen tetroxide is a component of [[smog]] containing nitrogen dioxide.

Solid {{chem2|N2O4}} is white, and melts at −11.2&nbsp;°C.<ref name=HW/>

==Production==
Nitrogen tetroxide is made by the [[catalytic oxidation]] of [[ammonia]] (the [[Ostwald process]]): steam is used as a [[diluent]] to reduce the combustion temperature. In the first step, the ammonia is oxidized into [[nitric oxide]]:
: 4 NH<sub>3</sub> + 5 O<sub>2</sub> → 4 NO + 6 H<sub>2</sub>O

Most of the water is condensed out, and the gases are further cooled; the nitric oxide that was produced is oxidized to nitrogen dioxide, which is then dimerized into nitrogen tetroxide:
: 2 NO + O<sub>2</sub> → 2 NO<sub>2</sub>
: 2 NO<sub>2</sub> ⇌ N<sub>2</sub>O<sub>4</sub>

and the remainder of the water is removed as [[nitric acid]]. The gas is essentially pure nitrogen dioxide, which is condensed into dinitrogen tetroxide in a brine-cooled liquefier.<ref>{{cite book |last1=Hebry |first1=TH |last2=Inskeep |first2=GC |title=Modern Chemical Processes: A Series of Articles Describing Chemical Manufacturing Plants |date=1954 |publisher=Reinhold |location=New York |page=219 |url=https://books.google.com/books?id=-L3nAAAAMAAJ |language=en}}</ref>

Dinitrogen tetroxide can also be made through the reaction of concentrated nitric acid and metallic copper. This synthesis is practical in a laboratory setting. Dinitrogen tetroxide can also be produced by heating metal nitrates.<ref>{{cite book |last1=Rennie |first1=Richard |title=A Dictionary of Chemistry |date=2016 |publisher=Oxford University Press |isbn=978-0-19-872282-3 |page=178 |url=https://books.google.com/books?id=d1sFCwAAQBAJ&pg=PA178 |language=en}}</ref> The oxidation of copper by nitric acid is a complex reaction forming various nitrogen oxides of varying stability which depends on the concentration of the nitric acid, presence of oxygen, and other factors. The unstable species further react to form nitrogen dioxide which is then purified and condensed to form dinitrogen tetroxide.

==Use as a rocket propellant==
Nitrogen tetroxide is used as an oxidizing agent in one of the most important rocket propellant systems because it can be stored as a liquid at room temperature. [[Pedro Paulet]], a [[Peruvian]] [[polymath]], reported in 1927 that he had experimented in the 1890s with a rocket engine that used spring-loaded nozzles that periodically introduced vaporized nitrogen tetroxide and a [[petroleum benzine]] to a [[spark plug]] for ignition, with the engine putting out 300 pulsating explosions per minute.<ref>{{Cite web |last=Gonzales Obando |first=Diana |date=2021-07-22 |title=Pedro Paulet: el genio peruano que se adelantó a su época y fundó la era espacial |url=https://elcomercio.pe/eldominical/ciencia/pedro-paulet-el-genio-peruano-que-fundo-la-era-espacial-noticia/ |access-date=2022-03-13 |website=[[El Comercio (Peru)|El Comercio]] |language=es}}</ref><ref>{{Cite web |last= |first= |date=25 August 1927 |title=Un peruano Pedro Paulet reclama la propiedad de su invento |url=https://elcomercio.pe/bicentenario/1927-l-el-buque-cohete-un-peruano-pedro-paulet-reclama-la-propiedad-de-su-invento-l-bicentenario-noticia/ |access-date=2022-03-13 |website=[[El Comercio (Peru)|El Comercio]] |language=es}}</ref> Paulet would go on to visit the German rocket association [[Verein für Raumschiffahrt|Verein für Raumschiffahrt (VfR)]] and on March 15, 1928, Valier applauded Paulet's liquid-propelled rocket design in the VfR publication ''Die Rakete'', saying the engine had "amazing power".<ref>{{cite book |last1=Mejía |first1=Álvaro |url=https://revistas.ucsp.edu.pe/index.php/persona/article/view/209/230 |title=Pedro Paulet, sabio multidisciplinario |publisher=Universidad Católica San Pablo |year=2017 |isbn= |edition= |location= |pages=95–122 |language=es |access-date=}}</ref> Paulet would soon be approached by [[Nazi Germany]] to help develop rocket technology, though he refused to assist and never shared the formula for his propellant.<ref name=":03">{{Cite news |title=El peruano que se convirtió en el padre de la astronáutica inspirado por Julio Verne y que aparece en los nuevos billetes de 100 soles |language=es |work=[[BBC News]] |url=https://www.bbc.com/mundo/noticias-america-latina-38197437 |access-date=2022-03-11}}</ref>

In early 1944, research on the usability of dinitrogen tetroxide as an oxidizing agent for rocket fuel was conducted by German scientists, although the Germans only used it to a very limited extent as an additive for [[S-Stoff]] (fuming nitric acid). It became the storable oxidizer of choice for many rockets in both the [[United States]] and [[USSR]] by the late 1950s. It is a [[hypergolic propellant]] in combination with a [[hydrazine]]-based [[rocket propellant|rocket fuel]]. One of the earliest uses of this combination was on the [[Titan (rocket family)|Titan family of rockets]] used originally as [[Intercontinental ballistic missile|ICBMs]] and then as [[launch vehicle]]s for many spacecraft. Used on the U.S. [[Project Gemini|Gemini]] and [[Apollo program|Apollo]] spacecraft and also on the [[Space Shuttle]], it continues to be used as station-keeping propellant on most geo-stationary satellites, and many deep-space probes. It is also the primary oxidizer for Russia's [[Proton (rocket)|Proton rocket]].

When used as a propellant, dinitrogen tetroxide is usually referred to simply as ''nitrogen tetroxide'' and the abbreviation ''NTO'' is extensively used. Additionally, NTO is often used with the addition of a small percentage of [[nitric oxide]] that reacts to form [[dinitrogen trioxide]], which inhibits [[stress-corrosion cracking]] of titanium alloys, and in this form, propellant-grade NTO is referred to as ''[[mixed oxides of nitrogen]]'' (''MON'') and can be distinguished by its green-blue color. Larger additions of nitric oxide, up to 25-30%, also lower the freezing point of NTO, improving storability in space conditions.<ref>{{Cite encyclopedia |title=Dinitrogen Tetroxide |chapter=N<sub>2</sub>O<sub>4</sub>/N<sub>2</sub>O<sub>3</sub> Mixtures|encyclopedia=Encyclopedia of Oxidizers |publisher=De Gruyter |last= Schmidt |first=Eckart W. |volume=1|date=2022 |pages=437–453 |doi=10.1515/9783110750294-005 |isbn=978-3-11-075029-4}}</ref> Most spacecraft now use MON instead of NTO; for example, the Space Shuttle reaction control system used MON3 (NTO containing 3% NO by weight).<ref>{{Cite web | url=http://www.friends-partners.org/partners/mwade/props/rocindex.htm | title=Rocket Propellant Index | access-date=2005-03-01 | archive-url=https://web.archive.org/web/20080511232517/http://www.friends-partners.org/partners/mwade/props/rocindex.htm | archive-date=2008-05-11 | url-status=dead }}</ref>

===The Apollo-Soyuz mishap===
On 24 July 1975, NTO poisoning affected three U.S. [[astronaut]]s on the final descent to Earth after the [[Apollo-Soyuz Test Project]] flight. This was due to a switch accidentally left in the wrong position, which allowed the [[Spacecraft attitude control|attitude control]] thrusters to fire after the cabin fresh air intake was opened, allowing NTO fumes to enter the cabin. One crew member lost consciousness during descent. Upon landing, the crew was hospitalized for five days for chemical-induced [[pneumonia]] and [[pulmonary edema]].<ref>[https://news.google.com/newspapers?id=RBgsAAAAIBAJ&sjid=kMgEAAAAIBAJ&dq=apollo%20gas&pg=993%2C1384026 "Brand Takes Blame For Apollo Gas Leak"], ''Florence, AL - Times Daily newspaper'', August 10, 1975</ref><ref>Sotos, John G., MD. [http://www.doctorzebra.com/drz/s_medhx.html#ASTP_incident "Astronaut and Cosmonaut Medical Histories"], May 12, 2008, accessed April 1, 2011.</ref>

==Power generation using N<sub>2</sub>O<sub>4</sub>==
The tendency of N<sub>2</sub>O<sub>4</sub> to reversibly break into NO<sub>2</sub> has led to research into its use in advanced power generation systems as a so-called dissociating gas.<ref>{{cite tech report |first=Robert J. |last=Stochl |title=Potential performance improvement by using a reacting gas (nitrogen tetroxide) as the working fluid in a closed Brayton cycle |number=TM-79322 |institution=[[NASA]] |year=1979 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19800008230.pdf}}</ref> "Cool" dinitrogen tetroxide is compressed and heated, causing it to dissociate into [[nitrogen dioxide]] at half the molecular weight. This hot nitrogen dioxide is expanded through a turbine, cooling it and lowering the pressure, and then cooled further in a heat sink, causing it to recombine into nitrogen tetroxide at the original molecular weight.  It is then much easier to compress to start the entire cycle again. Such dissociative gas [[Brayton cycle]]s have the potential to considerably increase efficiencies of power conversion equipment.<ref>{{cite web|last=Ragheb|first=R.|title=Nuclear Reactors Concepts and Thermodynamic Cycles|url=http://mragheb.com/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engineering/Nuclear%20Reactors%20Concepts%20and%20Thermodynamic%20Cycles.pdf|access-date=1 May 2013}}</ref>

The high molecular weight and smaller volumetric expansion ratio of nitrogen dioxide compared to steam allows the turbines to be more compact.<ref>{{Cite journal |last1=Binotti |first1=Marco |last2=Invernizzi |first2=Costante M. |last3=Iora |first3=Paolo |last4=Manzolini |first4=Giampaolo |date=March 2019 |title=Dinitrogen tetroxide and carbon dioxide mixtures as working fluids in solar tower plants |url=https://linkinghub.elsevier.com/retrieve/pii/S0038092X1930091X |journal=Solar Energy |language=en |volume=181 |pages=203–213 |doi=10.1016/j.solener.2019.01.079|s2cid=104462066 |url-access=subscription }}</ref>

N<sub>2</sub>O<sub>4</sub> was the main component of the "nitrin" working fluid in the decommissioned [[Pamir-630D]] portable nuclear reactor which operated from 1985 to 1987.<ref>{{Cite web |last=Paliukhovich |first=V.M. |date=7 May 2023 |title=Safe Decommissioning of Mobile Nuclear Power Plant |url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/33/052/33052291.pdf |url-status=live |archive-url=https://web.archive.org/web/20230507105914/https://inis.iaea.org/collection/NCLCollectionStore/_Public/33/052/33052291.pdf |archive-date=7 May 2023 |access-date=7 May 2023 |website=International Atomic Energy Agency |publisher=Department for Supervision of Industrial and Nuclear Safety |publication-place=Minsk, Belarus}}</ref>

==Chemical reactions==

===Intermediate in the manufacture of nitric acid===
Nitric acid is manufactured on a large scale via  N<sub>2</sub>O<sub>4</sub>.  This species reacts with water to give both [[nitrous acid]] and [[nitric acid]]:
: N<sub>2</sub>O<sub>4</sub> + H<sub>2</sub>O → HNO<sub>2</sub> + HNO<sub>3</sub>

The coproduct HNO<sub>2</sub> upon heating [[Disproportionation|disproportionates]] to [[Nitric oxide|NO]] and more nitric acid. When exposed to oxygen, NO is converted back into nitrogen dioxide:
: 2 NO + O<sub>2</sub> → 2 NO<sub>2</sub>

The resulting NO<sub>2</sub> and N<sub>2</sub>O<sub>4</sub> can be returned to the cycle to give the mixture of nitrous and nitric acids again.

===Synthesis of metal nitrates===
N<sub>2</sub>O<sub>4</sub> undergoes [[molecular autoionization]] to give [NO<sup>+</sup>] [NO<sub>3</sub><sup>−</sup>], with the former [[nitrosonium]] ion being a strong oxidant. Various anhydrous [[transition metal nitrate complex]]es can be prepared from N<sub>2</sub>O<sub>4</sub> and base metal.<ref>{{cite journal |last1=Addison |first1=C. Clifford |title=Dinitrogen tetroxide, nitric acid, and their mixtures as media for inorganic reactions |journal=Chemical Reviews |date=February 1980 |volume=80 |issue=1 |pages=21–39 |doi=10.1021/cr60323a002}}</ref>

: 2 N<sub>2</sub>O<sub>4</sub> + M → 2 NO + M(NO<sub>3</sub>)<sub>2</sub>

where M = [[copper|Cu]], [[zinc|Zn]], or [[tin|Sn]].

If metal nitrates are prepared from N<sub>2</sub>O<sub>4</sub> in completely anhydrous conditions, a range of covalent metal nitrates can be formed with many transition metals. This is because there is a thermodynamic preference for the nitrate ion to bond covalently with such metals rather than form an ionic structure. Such compounds must be prepared in anhydrous conditions, since the nitrate ion is a much weaker ligand than water, and if water is present the simple nitrate of the [[Metal aquo complex|hydrated metal ion]] will form. The anhydrous nitrates concerned are themselves covalent, and many, e.g. anhydrous [[copper nitrate]], are volatile at room temperature. Anhydrous titanium nitrate sublimes in vacuum at only 40&nbsp;°C. Many of the anhydrous transition metal nitrates have striking colours. This branch of chemistry was developed by [[Cliff Addison]] and Norman Logan at the [[University of Nottingham]] in the UK during the 1960s and 1970s when highly efficient desiccants and [[dry box]]es started to become available.

===With organic compounds===
In even slightly basic solvents, N<sub>2</sub>O<sub>4</sub> adds to [[alkene]]s radically, giving mixtures of [[nitro compound]]s and [[nitrite ester]]s.  Pure or in entirely nonbasic solvents, the compounds autoionizes as above, to give [[nitroso compound]]s and [[nitrate ester]]s.<ref>{{cite book|title=Nitrosation|first=D.&nbsp;L.&nbsp;H.|last=Williams|publisher=[[Cambridge University Press|Cambridge University]]|location=Cambridge, UK|year=1988|isbn=0-521-26796-X|url=https://archive.org/details/nitrosation0000will|url-access=registration|pages=49–50}}</ref>

==References==
{{reflist}}

== Further reading ==
*{{Cite encyclopedia |title=Dinitrogen Tetroxide |encyclopedia=Encyclopedia of Oxidizers |publisher=De Gruyter |last= Schmidt |first=Eckart W. |volume=1|date=2022 |pages=367–624 |doi=10.1515/9783110750294-005 |isbn=978-3-11-075029-4}}
*{{Cite thesis |last=Head |first=Andrew W. |title=Nitrogen Tetroxide to Mixed Oxides of Nitrogen: History, Usage, Synthesis, and Composition Determination |date=2021 |degree=MSc |publisher=Purdue University |url=https://hammer.purdue.edu/articles/thesis/Nitrogen_Tetroxide_to_Mixed_Oxides_of_Nitrogen_History_Usage_Synthesis_and_Composition_Determination/17003098/1 |doi=10.25394/PGS.17003098.V1}}
* Nitrogen Dioxide in Workplace Atmospheres, osha.gov, May 1987, revised May 2001

==External links==
{{Commons}}
* [https://www.ilo.org/dyn/icsc/showcard.display?p_lang=en&p_card_id=0930&p_version=2 International Chemical Safety Card 0930]
* [https://web.archive.org/web/20040205090004/http://www.npi.gov.au/database/substance-info/profiles/67.html National Pollutant Inventory – Oxides of nitrogen fact sheet]
* [https://www.cdc.gov/niosh/npg/npgd0454.html NIOSH Pocket Guide to Chemical Hazards]: Nitrogen tetroxide
* [http://encyclopedia.airliquide.com/encyclopedia.asp?LanguageID=11&CountryID=19&Formula=N2O4&GasID=0&UNNumber=&btnFormula.x=0&btnFormula.y=0#MSDS Air Liquide Gas Encyclopedia: NO<sub>2</sub> / N<sub>2</sub>O<sub>4</sub>] {{Webarchive|url=https://web.archive.org/web/20160310185602/http://encyclopedia.airliquide.com/encyclopedia.asp?btnformula.x=0&btnformula.y=0&countryid=19&formula=n2o4&gasid=0&languageid=11&unnumber=#MSDS |date=2016-03-10 }}
* {{cite web|last=Poliakoff|first=Martyn|title=The Chemistry of Lunar Lift-Off: Our Apollo 11 40th Anniversary Special|url=http://www.periodicvideos.com/videos/feature_lunar_liftoff.htm|work=[[The Periodic Table of Videos]]|publisher=[[University of Nottingham]]|author-link=Martyn Poliakoff|year=2009}}

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{{Oxides}}
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{{DEFAULTSORT:Dinitrogen Tetroxide}}
[[Category:Nitrogen oxides]]
[[Category:Rocket oxidizers]]
[[Category:Oxidizing agents]]
[[Category:Gases with color]]