Dinitrogen tetroxide

Last updated
Dinitrogen tetroxide
Full structural formula Dinitrogen tetroxide.svg
Full structural formula
Space-filling model Dinitrogen-tetroxide-3D-vdW.png
Space-filling model
Nitrogen dioxide at different temperatures.jpg
Nitrogen dioxide at −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 to NO
2 at higher temperatures.
Names
IUPAC name
Dinitrogen tetroxide
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.031.012 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 234-126-4
2249
PubChem CID
RTECS number
  • QW9800000
UNII
UN number 1067
  • InChI=1S/N2O4/c3-1(4)2(5)6 Yes check.svgY
    Key: WFPZPJSADLPSON-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/N2O4/c3-1(4)2(5)6
    Key: WFPZPJSADLPSON-UHFFFAOYAS
  • [O-][N+](=O)[N+]([O-])=O
Properties
N2O4
Molar mass 92.010 g·mol−1
AppearanceWhite solid, colorless liquid, orange gas
Density 1.44246 g/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 96 kPa (20 °C) [1]
−23.0·10−6 cm3/mol
1.00112
Structure
Planar, D2h
small, non-zero
Thermochemistry
Std molar
entropy (S⦵298)
304.29 J/K⋅mol [2]
+9.16 kJ/mol [2]
Hazards
GHS labelling:
GHS-pictogram-rondflam.svg GHS-pictogram-acid.svg GHS-pictogram-skull.svg GHS-pictogram-exclam.svg
Danger
H270, 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)
[3] [4]
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
3
0
0
OX
Flash point Non-flammable
Safety data sheet (SDS) External SDS
Related compounds
Related nitrogen oxides
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide (NTO), and occasionally (usually among ex-USSR/Russian rocket engineers) as amyl, is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium mixture with nitrogen dioxide. Its molar mass is 92.011 g/mol.

Contents

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 groups (-NO2) bonded together. It forms an equilibrium mixture with nitrogen dioxide. [5] The molecule is planar with an N-N bond distance of 1.78 Å and N-O distances of 1.19 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 Å. [6] This exceptionally weak σ bond (amounting to overlapping of the sp2 hybrid orbitals of the two NO2 units [7] ) results from the simultaneous delocalization of the bonding electron pair across the whole N2O4 molecule, and the considerable electrostatic repulsion of the doubly occupied molecular orbitals of each NO2 unit. [8]

Unlike NO2, N2O4 is diamagnetic since it has no unpaired electrons. [9] The liquid is also colorless but can appear as a brownish yellow liquid due to the presence of NO2 according to the following equilibrium: [9]

N2O4 ⇌ 2 NO2 (ΔH = +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 N2O4 is white, and melts at −11.2 °C. [9]

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 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 as nitric acid. The gas is essentially pure nitrogen dioxide, which is condensed into dinitrogen tetroxide in a brine-cooled liquefier. [10]

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. [11] 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. [12] [13] Paulet would go on to visit the German rocket association 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". [14] 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. [15]

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 fuel. One of the earliest uses of this combination was on the Titan family of rockets used originally as ICBMs and then as launch vehicles for many spacecraft. Used on the U.S. Gemini and 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.

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, which inhibits stress-corrosion cracking of titanium alloys, and in this form, propellant-grade NTO is referred to as mixed 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). [16]

The Apollo-Soyuz mishap

On 24 July 1975, NTO poisoning affected three U.S. astronauts 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 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. [17] [18]

Power generation using N2O4

The tendency of N2O4 to reversibly break into NO2 has led to research into its use in advanced power generation systems as a so-called dissociating gas. [19] "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 cycles have the potential to considerably increase efficiencies of power conversion equipment. [20]

The high molecular weight and smaller volumetric expansion ratio of nitrogen dioxide compared to steam allows the turbines to be more compact. [21]

N2O4 was the main component of the "nitrin" working fluid in the decommissioned Pamir-630D portable nuclear reactor which operated from 1985 to 1987. [22]

Chemical reactions

Intermediate in the manufacture of nitric acid

Nitric acid is manufactured on a large scale via N2O4. This species reacts with water to give both nitrous acid and nitric acid:

N2O4 + H2O → HNO2 + HNO3

The coproduct HNO2 upon heating disproportionates to NO and more nitric acid. When exposed to oxygen, NO is converted back into nitrogen dioxide:

2 NO + O2 → 2 NO2

The resulting NO2 and N2O4 can be returned to the cycle to give the mixture of nitrous and nitric acids again.

Synthesis of metal nitrates

N2O4 undergoes molecular autoionization to give [NO+] [NO3−], with the former nitrosonium ion being a strong oxidant. Various anhydrous transition metal nitrate complexes can be prepared from N2O4 and base metal. [23]

2 N2O4 + M → 2 NO + M(NO3)2

where M = Cu, Zn, or Sn.

If metal nitrates are prepared from N2O4 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 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 °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 boxes started to become available.

With organic compounds

In even slightly basic solvents, N2O4 adds to alkenes radically, giving mixtures of nitro compounds and nitrite esters. Pure or in entirely nonbasic solvents, the compounds autoionizes as above, to give nitroso compounds and nitrate esters. [24]

Related Research Articles

<span class="mw-page-title-main">Nitrogen</span> Chemical element with atomic number 7 (N)

Nitrogen is a chemical element; it has symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bond to form N2, a colourless and odourless diatomic gas. N2 forms about 78% of Earth's atmosphere, making it the most abundant chemical species in air. Because of the volatility of nitrogen compounds, nitrogen is relatively rare in the solid parts of the Earth.

<span class="mw-page-title-main">Nitric acid</span> Highly corrosive mineral acid

Nitric acid is an inorganic compound with the formula HNO3. It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into oxides of nitrogen. Most commercially available nitric acid has a concentration of 68% in water. When the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as red fuming nitric acid at concentrations above 86%, or white fuming nitric acid at concentrations above 95%.

<span class="mw-page-title-main">Nitronium ion</span> Polyatomic ion

The nitronium ion, [NO2]+, is a cation. It is an onium ion because its nitrogen atom has +1 charge, similar to ammonium ion [NH4]+. It is created by the removal of an electron from the paramagnetic nitrogen dioxide molecule NO2, or the protonation of nitric acid HNO3.

<span class="mw-page-title-main">Oxide</span> Chemical compound where oxygen atoms are combined with atoms of other elements

An oxide is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– ion with oxygen in the oxidation state of −2. Most of the Earth's crust consists of oxides. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 that protects the foil from further oxidation.

<span class="mw-page-title-main">Oxidizing agent</span> Chemical compound used to oxidize another substance in a chemical reaction

An oxidizing agent is a substance in a redox chemical reaction that gains or "accepts"/"receives" an electron from a reducing agent. In other words, an oxidizer is any substance that oxidizes another substance. The oxidation state, which describes the degree of loss of electrons, of the oxidizer decreases while that of the reductant increases; this is expressed by saying that oxidizers "undergo reduction" and "are reduced" while reducers "undergo oxidation" and "are oxidized". Common oxidizing agents are oxygen, hydrogen peroxide, and the halogens.

<span class="mw-page-title-main">Red fuming nitric acid</span> Chemical compound

Red fuming nitric acid (RFNA) is a storable oxidizer used as a rocket propellant. It consists of 84% nitric acid, 13% dinitrogen tetroxide and 1–2% water. The color of red fuming nitric acid is due to the dinitrogen tetroxide, which breaks down partially to form nitrogen dioxide. The nitrogen dioxide dissolves until the liquid is saturated, and produces toxic fumes with a suffocating odor. RFNA increases the flammability of combustible materials and is highly exothermic when reacting with water.

<span class="mw-page-title-main">Nitrogen dioxide</span> Chemical compound with formula NO₂

Nitrogen dioxide is a chemical compound with the formula NO2. One of several nitrogen oxides, nitrogen dioxide is a reddish-brown gas. It is a paramagnetic, bent molecule with C2v point group symmetry. Industrially, NO2 is an intermediate in the synthesis of nitric acid, millions of tons of which are produced each year, primarily for the production of fertilizers.

Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:

<span class="mw-page-title-main">Copper(II) nitrate</span> Chemical compound

Copper(II) nitrate describes any member of the family of inorganic compounds with the formula Cu(NO3)2(H2O)x. The hydrates are hygroscopic blue solids. Anhydrous copper nitrate forms blue-green crystals and sublimes in a vacuum at 150-200 °C. Common hydrates are the hemipentahydrate and trihydrate.

<span class="mw-page-title-main">Dinitrogen pentoxide</span> Chemical compound

Dinitrogen pentoxide is the chemical compound with the formula N2O5. It is one of the binary nitrogen oxides, a family of compounds that contain only nitrogen and oxygen. It exists as colourless crystals that sublime slightly above room temperature, yielding a colorless gas.

The chemical element nitrogen is one of the most abundant elements in the universe and can form many compounds. It can take several oxidation states; but the most common oxidation states are -3 and +3. Nitrogen can form nitride and nitrate ions. It also forms a part of nitric acid and nitrate salts. Nitrogen compounds also have an important role in organic chemistry, as nitrogen is part of proteins, amino acids and adenosine triphosphate.

Mixed oxides of nitrogen (MON) are solutions of nitric oxide (NO) in dinitrogen tetroxide/nitrogen dioxide (N2O4 and NO2). It may be used as an oxidizing agent in rocket propulsion systems. A broad range of compositions is available, and can be denoted as MONi, where i represents the percentage of nitric oxide in the mixture (e.g. MON3 contains 3% nitric oxide, MON25 25% nitric oxide). An upper limit is MON40 (40% by weight). In Europe MON 1.3 is mostly used for rocket propulsion systems, while NASA seems to prefer MON 3. A higher percentage of NO decreases the corrosiveness and oxidation potential of the liquid, but increases costs.

Tetranitromethane or TNM is an organic oxidizer with chemical formula C(NO2)4. Its chemical structure consists of four nitro groups attached to one carbon atom. In 1857 it was first synthesised by the reaction of sodium cyanoacetamide with nitric acid.

<span class="mw-page-title-main">Dinitrogen trioxide</span> Chemical compound

Dinitrogen trioxide is the inorganic compound with the formula N2O3. It is a nitrogen oxide. It forms upon mixing equal parts of nitric oxide and nitrogen dioxide and cooling the mixture below −21 °C (−6 °F):

<span class="mw-page-title-main">Tetranitratoaluminate</span> Chemical compound

Tetranitratoaluminate is an anion of aluminium and nitrate groups with formula [Al(NO3)4]− that can form salts called tetranitratoaluminates. It is unusual in being a nitrate complex of a light element.

<span class="mw-page-title-main">Sodium hyponitrite</span> Chemical compound

Sodium hyponitrite is a solid ionic compound with formula Na
2N
2O
2 or (Na+
)2[ON=NO]2−.

<span class="mw-page-title-main">Titanium(IV) nitrate</span> Chemical compound

Titanium nitrate is the inorganic compound with formula Ti(NO3)4. It is a colorless, diamagnetic solid that sublimes readily. It is an unusual example of a volatile binary transition metal nitrate. Ill defined species called titanium nitrate are produced upon dissolution of titanium or its oxides in nitric acid.

<span class="mw-page-title-main">Tin(IV) nitrate</span> Chemical compound

Tin(IV) nitrate is a salt of tin with nitric acid. It is a volatile white solid, subliming at 40 °C under a vacuum. Unlike other nitrates, it reacts with water to produce nitrogen dioxide.

<span class="mw-page-title-main">Transition metal nitrate complex</span> Compound of nitrate ligands

A transition metal nitrate complex is a coordination compound containing one or more nitrate ligands. Such complexes are common starting reagents for the preparation of other compounds.

<span class="mw-page-title-main">Nitrosyl perchlorate</span> Chemical compound

Nitrosyl perchlorate is the inorganic compound with the formula NO(ClO4). A hygroscopic white solid, it is the salt of the nitrosonium cation with the perchlorate anion. It is an oxidant and strong electrophile, but has fallen out of use with the availability of the closely related salt nitrosonium tetrafluoroborate NO(BF4).

References

  1. ↑ International Chemical Safety Card https://www.ilo.org/dyn/icsc/showcard.display?p_lang=en&p_card_id=0930&p_version=2
  2. 1 2 P.W. Atkins and J. de Paula, Physical Chemistry (8th ed., W.H. Freeman, 2006) p.999
  3. ↑ "Chemical Datasheet: Nitrogen tetroxide". CAMEO Chemicals NOAA . Retrieved 8 September 2020.
  4. ↑ "Compound Summary: Dinitrogen tetroxide". PubChem . Retrieved 8 September 2020.
  5. ↑ Bent, Henry A. (1963). "Dimers of Nitrogen Dioxide. II. Structure and Bonding". Inorganic Chemistry. 2 (4): 747–752. doi:10.1021/ic50008a020.
  6. ↑ 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. ISBN   978-0-13-014329-7. LCCN   2001032331. OCLC   46872308.
  7. ↑ Rayner-canham, Geoff (2013). Descriptive inorganic chemistry (6th ed.). p. 400. ISBN   978-1-319-15411-0. OCLC   1026755795.
  8. ↑ 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. ISSN   0002-7863.
  9. 1 2 3 Holleman, A. F.; Wiberg, E. (2001) Inorganic Chemistry. Academic Press: San Diego. ISBN   978-0-12-352651-9.
  10. ↑ Hebry, TH; Inskeep, GC (1954). Modern Chemical Processes: A Series of Articles Describing Chemical Manufacturing Plants. New York: Reinhold. p. 219.
  11. ↑ Rennie, Richard (2016). A Dictionary of Chemistry. Oxford University Press. p. 178. ISBN   978-0-19-872282-3.
  12. ↑ 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). Retrieved 2022-03-13.
  13. ↑ "Un peruano Pedro Paulet reclama la propiedad de su invento". El Comercio (in Spanish). 25 August 1927. Retrieved 2022-03-13.
  14. ↑ Mejía, Álvaro (2017). Pedro Paulet, sabio multidisciplinario (in Spanish). Universidad Católica San Pablo. pp. 95–122.
  15. ↑ "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). Retrieved 2022-03-11.
  16. ↑ "Rocket Propellant Index". Archived from the original on 2008-05-11. Retrieved 2005-03-01.
  17. ↑ "Brand Takes Blame For Apollo Gas Leak", Florence, AL - Times Daily newspaper, August 10, 1975
  18. ↑ Sotos, John G., MD. "Astronaut and Cosmonaut Medical Histories", May 12, 2008, accessed April 1, 2011.
  19. ↑ 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.
  20. ↑ Ragheb, R. "Nuclear Reactors Concepts and Thermodynamic Cycles" (PDF). Retrieved 1 May 2013.
  21. ↑ 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. S2CID   104462066.
  22. ↑ 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. Retrieved 7 May 2023.
  23. ↑ 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.
  24. ↑ Williams, D. L. H. (1988). Nitrosation . Cambridge, UK: Cambridge University. pp. 49–50. ISBN   0-521-26796-X.

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