Dinitrogen tetroxide
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 Nitrogen dioxideat −196 °C, 0 °C, 23 °C, 35 °C, and 50 °C. (NO
2) converts to the colorless dinitrogen tetroxide (N 2O 4) at low temperatures, and reverts toNO 2at higher temperatures. | |||
| Names | |||
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| IUPAC name
Dinitrogen tetroxide
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| Identifiers | |||
3D model (JSmol)
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| ChEBI | |||
| ChemSpider | |||
| ECHA InfoCard | 100.031.012 | ||
| EC Number |
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| 2249 | |||
PubChemCID
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| RTECS number |
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| UNII | |||
| UN number | 1067 | ||
CompTox Dashboard(EPA)
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| Properties | |||
| N2O4 | |||
| Molar mass | 92.010g·mol−1 | ||
| Appearance | White solid, colorless liquid, orange gas | ||
| Density | 1.44246g/cm3(liquid, 21 °C) | ||
| Melting point | −11.2 °C (11.8 °F; 261.9 K) and decomposes to NO2 | ||
| Boiling point | 21.69 °C (71.04 °F; 294.84 K) | ||
| Reacts to form nitrous and nitric acids | |||
| Vapor pressure | 96kPa (20°C)[1] | ||
| −23.0·10−6cm3/mol | |||
Refractive index(nD)
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1.00112 | ||
| Structure | |||
| Planar,D2h | |||
| small, non-zero | |||
| Thermochemistry | |||
Std molar
entropy(S⦵298) |
304.29J/K⋅mol[2] | ||
Std enthalpy of
formation(ΔfH⦵298) |
+9.16kJ/mol[2] | ||
| Hazards | |||
| GHSlabelling: | |||
    
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| Danger | |||
| H270,H280,H314,H330,H335,H336 | |||
| P220,P244,P260,P261,P264,P271,P280,P284,P301+P330+P331,P303+P361+P353,P304+P340,P305+P351+P338,P310,P312,P320,P321,P363,P370+P376,P403,P403+P233,P405,P410+P403,P501 | |||
| NFPA 704(fire diamond) | |||
| Flash point | Non-flammable | ||
| Safety data sheet(SDS) | External SDS | ||
| Related compounds | |||
Related compounds
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Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).
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Dinitrogen tetroxide,commonly referred to asnitrogen tetroxide(NTO), and occasionally (usually among ex-USSR/Russian rocket engineers) asamyl,is thechemical compoundN2O4.It is a usefulreagentin chemical synthesis. It forms anequilibrium mixturewithnitrogen dioxide.Its molar mass is 92.011 g/mol.
Dinitrogen tetroxide is a powerfuloxidizerthat ishypergolic(spontaneously reacts) upon contact with various forms ofhydrazine,which has made the pair a commonbipropellantfor rockets.
Structure and properties[edit]
Dinitrogen tetroxide could be regarded as twonitro groups(-NO2) bonded together. It forms anequilibrium mixturewithnitrogen dioxide.[5]The molecule is planar with an N-N bond distance of 1.78Å and N-O distances of 1.19Å. The N-N distance corresponds to a weak bond, since it is significantly longer than the average N-N single bond length of 1.45Å.[6]This exceptionally weak σ bond (amounting to overlapping of thesp2hybrid orbitals of the two NO2units[7]) results from the simultaneous delocalization of the bonding electron pair across the whole N2O4molecule, and the considerable electrostatic repulsion of the doubly occupied molecular orbitals of each NO2unit.[8]
Unlike NO2,N2O4isdiamagneticsince it has no unpaired electrons.[9]The liquid is also colorless but can appear as a brownish yellow liquid due to the presence of NO2according to the following equilibrium:[10]
- N2O4⇌ 2 NO2(ΔH= +57.23 kJ/mol)
Higher temperatures push the equilibrium towards nitrogen dioxide. Inevitably, some dinitrogen tetroxide is a component ofsmogcontaining nitrogen dioxide.
SolidN2O4is white, and melts at −11.2 °C.[11]
Production[edit]
Nitrogen tetroxide is made by thecatalyticoxidationofammonia(theOstwald process): steam is used as adiluentto reduce the combustion temperature. In the first step, the ammonia is oxidized intonitric oxide:
- 4 NH3+ 5 O2→ 4 NO + 6 H2O
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 + O2→ 2 NO2
- 2 NO2⇌ N2O4
and the remainder of the water is removed asnitric acid.The gas is essentially pure nitrogen dioxide, which is condensed into dinitrogen tetroxide in a brine-cooled liquefier.[12]
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.[13]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[edit]
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,aPeruvianpolymath,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 apetroleum benzineto aspark plugfor ignition, with the engine putting out 300 pulsating explosions per minute.[14][15]Paulet would go on to visit the German rocket associationVerein für Raumschiffahrt (VfR)and on March 15, 1928, Valier applauded Paulet's liquid-propelled rocket design in the VfR publicationDie Rakete,saying the engine had "amazing power".[16]Paulet would soon be approached byNazi Germanyto help develop rocket technology, though he refused to assist and never shared the formula for his propellant.[17]
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 forS-Stoff(fuming nitric acid). It became the storable oxidizer of choice for many rockets in both theUnited StatesandUSSRby the late 1950s. It is ahypergolic propellantin combination with ahydrazine-basedrocket fuel.One of the earliest uses of this combination was on theTitan family of rocketsused originally asICBMsand then aslaunch vehiclesfor many spacecraft. Used on the U.S.GeminiandApollospacecraft and also on theSpace 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'sProton rocket.
When used as a propellant, dinitrogen tetroxide is usually referred to simply asnitrogen tetroxideand the abbreviationNTOis extensively used. Additionally, NTO is often used with the addition of a small percentage ofnitric oxide,which inhibits stress-corrosion cracking of titanium alloys, and in this form, propellant-grade NTO is referred to asmixed oxides of nitrogen(MON). Most spacecraft now use MON instead of NTO; for example, the Space Shuttle reaction control system used MON3 (NTO containing 3% NO by weight).[18]
The Apollo-Soyuz mishap[edit]
On 24 July 1975, NTO poisoning affected three U.S.astronautson the final descent to Earth after theApollo-Soyuz Test Projectflight. This was due to a switch accidentally left in the wrong position, which allowed theattitude controlthrusters 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-inducedpneumoniaandedema.[19][20]
Power generation using N2O4[edit]
The tendency of N2O4to reversibly break into NO2has led to research into its use in advanced power generation systems as a so-called dissociating gas.[21]"Cool" dinitrogen tetroxide is compressed and heated, causing it to dissociate intonitrogen dioxideat 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 gasBrayton cycleshave the potential to considerably increase efficiencies of power conversion equipment.[22]
The high molecular weight and smaller volumetric expansion ratio of nitrogen dioxide compared to steam allows the turbines to be more compact.[23]
N2O4was the main component of the "nitrin" working fluid in the decommissionedPamir-630Dportable nuclear reactor which operated from 1985 to 1987.[24]
Chemical reactions[edit]
Intermediate in the manufacture of nitric acid[edit]
Nitric acid is manufactured on a large scale via N2O4.This species reacts with water to give bothnitrous acidandnitric acid:
- N2O4+ H2O → HNO2+ HNO3
The coproduct HNO2upon heatingdisproportionatestoNOand more nitric acid. When exposed to oxygen, NO is converted back into nitrogen dioxide:
- 2 NO + O2→ 2 NO2
The resulting NO2and N2O4can be returned to the cycle to give the mixture of nitrous and nitric acids again.
Synthesis of metal nitrates[edit]
N2O4undergoesmolecular autoionizationto give [NO+] [NO3−], with the formernitrosoniumion being a strong oxidant. Various anhydroustransition metal nitrate complexescan be prepared from N2O4and base metal.[25]
- 2 N2O4+ M → 2 NO + M(NO3)2
If metal nitrates are prepared from N2O4in 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 thehydrated metal ionwill form. The anhydrous nitrates concerned are themselves covalent, and many, e.g. anhydrouscopper nitrate,are volatile at room temperature. Anhydrous titanium nitrate sublimes in vacuum at only 40 °C. Many of the anhydrous transition metal nitrates have striking colours. This branch of chemistry was developed byCliff Addisonand Norman Logan at theUniversity of Nottinghamin the UK during the 1960s and 1970s when highly efficient desiccants anddry boxesstarted to become available.
References[edit]
- ^International Chemical Safety Cardhttps:// ilo.org/dyn/icsc/showcard.display?p_lang=en&p_card_id=0930&p_version=2
- ^abP.W. Atkins and J. de Paula,Physical Chemistry(8th ed., W.H. Freeman, 2006) p.999
- ^"Chemical Datasheet: Nitrogen tetroxide".CAMEO ChemicalsNOAA.Retrieved8 September2020.
- ^"Compound Summary: Dinitrogen tetroxide".PubChem.Retrieved8 September2020.
- ^Bent, Henry A. (1963). "Dimers of Nitrogen Dioxide. II. Structure and Bonding".Inorganic Chemistry.2(4): 747–752.doi:10.1021/ic50008a020.
- ^Petrucci, Ralph H.; Harwood, William S.; Herring, F. Geoffrey (2002).General chemistry: principles and modern applications(8th ed.). Upper Saddle River, N.J: Prentice Hall. p.420.ISBN978-0-13-014329-7.LCCN2001032331.OCLC46872308.
- ^Rayner-canham, Geoff (2013).Descriptive inorganic chemistry(6th ed.). p. 400.ISBN978-1-319-15411-0.OCLC1026755795.
- ^Ahlrichs, Reinhart; Keil, Frerich (1974-12-01)."Structure and bonding in dinitrogen tetroxide (N2O4)".Journal of the American Chemical Society.96(25): 7615–7620.doi:10.1021/ja00832a002.ISSN0002-7863.
- ^Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001.ISBN978-0-12-352651-9.
- ^Holleman, A. F.; Wiberg, E. (2001)Inorganic Chemistry.Academic Press: San Diego.ISBN0-12-352651-5.
- ^Holleman, A. F.; Wiberg, E. (2001)Inorganic Chemistry.Academic Press: San Diego.ISBN0-12-352651-5.
- ^Hebry, TH; Inskeep, GC (1954).Modern Chemical Processes: A Series of Articles Describing Chemical Manufacturing Plants.New York: Reinhold. p. 219.
- ^Rennie, Richard (2016).A Dictionary of Chemistry.Oxford University Press. p. 178.ISBN978-0-19-872282-3.
- ^Gonzales Obando, Diana (2021-07-22)."Pedro Paulet: el genio peruano que se adelantó a su época y fundó la era espacial".El Comercio(in Spanish).Retrieved2022-03-13.
- ^"Un peruano Pedro Paulet reclama la propiedad de su invento".El Comercio(in Spanish). 25 August 1927.Retrieved2022-03-13.
- ^Mejía, Álvaro (2017).Pedro Paulet, sabio multidisciplinario(in Spanish). Universidad Católica San Pablo. pp. 95–122.
- ^"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".BBC News(in Spanish).Retrieved2022-03-11.
- ^"Rocket Propellant Index".Archived fromthe originalon 2008-05-11.Retrieved2005-03-01.
- ^"Brand Takes Blame For Apollo Gas Leak",Florence, AL - Times Daily newspaper,August 10, 1975
- ^Sotos, John G., MD."Astronaut and Cosmonaut Medical Histories",May 12, 2008, accessed April 1, 2011.
- ^Stochl, Robert J. (1979).Potential performance improvement by using a reacting gas (nitrogen tetroxide) as the working fluid in a closed Brayton cycle(PDF)(Technical report).NASA.TM-79322.
- ^Ragheb, R."Nuclear Reactors Concepts and Thermodynamic Cycles"(PDF).Retrieved1 May2013.
- ^Binotti, Marco; Invernizzi, Costante M.; Iora, Paolo; Manzolini, Giampaolo (March 2019)."Dinitrogen tetroxide and carbon dioxide mixtures as working fluids in solar tower plants".Solar Energy.181:203–213.doi:10.1016/j.solener.2019.01.079.S2CID104462066.
- ^Paliukhovich, V.M. (7 May 2023)."Safe Decommissioning of Mobile Nuclear Power Plant"(PDF).International Atomic Energy Agency.Minsk, Belarus: Department for Supervision of Industrial and Nuclear Safety.Archived(PDF)from the original on 7 May 2023.Retrieved7 May2023.
- ^Addison, C. Clifford (February 1980). "Dinitrogen tetroxide, nitric acid, and their mixtures as media for inorganic reactions".Chemical Reviews.80(1): 21–39.doi:10.1021/cr60323a002.
External links[edit]
- International Chemical Safety Card 0930
- National Pollutant Inventory – Oxides of nitrogen fact sheet
- NIOSH Pocket Guide to Chemical Hazards:Nitrogen tetroxide
- Air Liquide Gas Encyclopedia: NO2/ N2O4Archived2016-03-10 at theWayback Machine
- Poliakoff, Martyn(2009)."The Chemistry of Lunar Lift-Off: Our Apollo 11 40th Anniversary Special".The Periodic Table of Videos.University of Nottingham.