Dinitrogen tetroxide
Encyclopedia
Dinitrogen tetroxide is the chemical compound
N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium mixture
with nitrogen dioxide
; some call this mixture dinitrogen tetroxide, while some call it nitrogen dioxide.
Dinitrogen tetroxide is a powerful oxidizer, making it highly toxic and corrosive. N2O4 is hypergolic with various forms of hydrazine
, i.e., they burn on contact without a separate ignition source, making them popular bipropellant rocket fuels.
with nitrogen dioxide
.
The molecule is planar with an N-N bond distance of 1.78 Å and N-O distances of 1.19 Å. Unlike NO2, N2O4 is diamagnetic
. It is also colorless but can appear as a brownish yellow liquid due to the presence of NO2 according to the following equilibrium:
Higher temperatures push the equilibrium towards nitrogen dioxide. Inevitably, some dinitrogen tetroxide is a component of smog
containing nitrogen dioxide.
: steam is used as a diluent
to reduce the combustion temperature. Most of the water is condensed out, and the gases are further cooled; the nitric oxide
that was produced is oxidized to nitrogen dioxide
, and the remainder of the water is removed as nitric acid
. The gas is essentially pure nitrogen tetroxide, which is condensed in a brine-cooled liquefier.
–based T-Stoff
oxidizer used in their World War II rocket-propelled combat aircraft designs such as the Messerschmitt Me 163
Komet, and by the late 1950s it became the storable oxidizer of choice for rockets in both the USA and USSR. It is a hypergolic propellant often used in combination with a hydrazine
-based rocket
fuel
. One of the earliest uses of this combination was on the Titan rocket
s used originally as ICBM
s and then as launch vehicle
s for many spacecraft. Used on the U.S. Gemini, Apollo spacecraft and the Space Shuttle, it continues to be used on most geo-stationary satellites, and many deep-space probes. It now seems likely that NASA will continue to use this oxidizer in the next-generation 'crew-vehicles' which will replace the shuttle. It is also the primary oxidizer for Russia's Proton rocket and China's Long March rockets.
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
" or "MON". Most spacecraft now use MON instead of NTO; for example, the Space Shuttle reaction control system uses MON3 (NTO containing 3wt%NO).
http://www.friends-partners.org/partners/mwade/props/rocindex.htm
On 24 July 1975, NTO poisoning nearly killed the three U.S. astronaut
s on board the Apollo-Soyuz Test Project
during its final descent. This was due to a switch left in the wrong position, which allowed NTO fumes to vent out of the Apollo spacecraft then back in through the cabin air intake from the outside air after the external vents were opened. One crewmember lost consciousness during descent. Upon landing, the crew was hospitalized 14 days for chemical-induced pneumonia
and edema
.
s have the potential to considerably increase efficiencies of power conversion equipment.
and nitric acid
:
The coproduct HNO2 upon heating disproportionate
s to NO
and more nitric acid. When exposed to oxygen, NO is converted back into nitrogen dioxide:
The resulting NO2 (and N2O4, obviously) can be returned to the cycle to give the mixture of nitrous and nitric acids again.
where M = Cu
, Zn
, or Sn
.
If metal nitrates are prepared from NTO 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 hydrated nitrate 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 degrees C. Many of the anhydrous transition metal nitrates have striking colours. This branch of chemistry was developed by Clifford Addisson and Noramn Logan at Nottingham University in the UK during the 1960s and 1970s when highly efficient desiccants and dry boxes started to become available.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium mixture
Chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...
with nitrogen dioxide
Nitrogen dioxide
Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...
; some call this mixture dinitrogen tetroxide, while some call it nitrogen dioxide.
Dinitrogen tetroxide is a powerful oxidizer, making it highly toxic and corrosive. N2O4 is hypergolic with various forms of hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
, i.e., they burn on contact without a separate ignition source, making them popular bipropellant rocket fuels.
Structure and properties
Dinitrogen tetroxide forms an equilibrium mixtureChemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...
with nitrogen dioxide
Nitrogen dioxide
Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...
.
The molecule is planar with an N-N bond distance of 1.78 Å and N-O distances of 1.19 Å. Unlike NO2, N2O4 is diamagnetic
Diamagnetism
Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Specifically, an external magnetic field alters the orbital velocity of electrons around their nuclei, thus changing the...
. It is also colorless but can appear as a brownish yellow liquid due to the presence of NO2 according to the following equilibrium:
- N2O4 2 NO2
Higher temperatures push the equilibrium towards nitrogen dioxide. Inevitably, some dinitrogen tetroxide is a component of smog
Smog
Smog is a type of air pollution; the word "smog" is a portmanteau of smoke and fog. Modern smog is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine...
containing nitrogen dioxide.
Production
Nitrogen dioxide is made by the catalytic oxidation of ammoniaAmmonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
: steam is used as a diluent
Diluent
A diluent is a diluting agent.Certain fluids are too viscous to be pumped easily or too dense to flow from one particular point to the other. This can be problematic, because it might not be economically feasible to transport such fluids in this state.To ease this restricted movement, diluents...
to reduce the combustion temperature. Most of the water is condensed out, and the gases are further cooled; the nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
that was produced is oxidized to nitrogen dioxide
Nitrogen dioxide
Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...
, and the remainder of the water is removed as nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
. The gas is essentially pure nitrogen tetroxide, which is condensed in a brine-cooled liquefier.
Use as a rocket propellant
Dinitrogen tetroxide is one of the most important rocket propellants ever developed, much like the German-developed hydrogen peroxideHydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
–based T-Stoff
T-Stoff
T-Stoff was the oxidizer part of a bipropellant rocket fuel combination used in Germany during World War II. It is a stabilized high test peroxide...
oxidizer used in their World War II rocket-propelled combat aircraft designs such as the Messerschmitt Me 163
Messerschmitt Me 163
The Messerschmitt Me 163 Komet, designed by Alexander Lippisch, was a German rocket-powered fighter aircraft. It is the only rocket-powered fighter aircraft ever to have been operational. Its design was revolutionary, and the Me 163 was capable of performance unrivaled at the time. Messerschmitt...
Komet, and by the late 1950s it became the storable oxidizer of choice for rockets in both the USA and USSR. It is a hypergolic propellant often used in combination with a hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
-based rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
. One of the earliest uses of this combination was on the Titan rocket
Titan (rocket family)
Titan was a family of U.S. expendable rockets used between 1959 and 2005. A total of 368 rockets of this family were launched, including all the Project Gemini manned flights of the mid-1960s...
s used originally as ICBM
Intercontinental ballistic missile
An intercontinental ballistic missile is a ballistic missile with a long range typically designed for nuclear weapons delivery...
s and then as launch vehicle
Launch vehicle
In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from the Earth's surface into outer space. A launch system includes the launch vehicle, the launch pad and other infrastructure....
s for many spacecraft. Used on the U.S. Gemini, Apollo spacecraft and the Space Shuttle, it continues to be used on most geo-stationary satellites, and many deep-space probes. It now seems likely that NASA will continue to use this oxidizer in the next-generation 'crew-vehicles' which will replace the shuttle. It is also the primary oxidizer for Russia's Proton rocket and China's Long March rockets.
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
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
, which inhibits stress-corrosion cracking of titanium alloys, and in this form, propellant-grade NTO is referred to as "Mixed Oxides of Nitrogen
Mixed Oxides of Nitrogen
Mixed oxides of nitrogen are solutions of nitric oxide in dinitrogen tetroxide/nitrogen dioxide . 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...
" or "MON". Most spacecraft now use MON instead of NTO; for example, the Space Shuttle reaction control system uses MON3 (NTO containing 3wt%NO).
http://www.friends-partners.org/partners/mwade/props/rocindex.htm
On 24 July 1975, NTO poisoning nearly killed the three U.S. astronaut
Astronaut
An astronaut or cosmonaut is a person trained by a human spaceflight program to command, pilot, or serve as a crew member of a spacecraft....
s on board the Apollo-Soyuz Test Project
Apollo-Soyuz Test Project
-Backup crew:-Crew notes:Jack Swigert had originally been assigned as the command module pilot for the ASTP prime crew, but prior to the official announcement he was removed as punishment for his involvement in the Apollo 15 postage stamp scandal.-Soyuz crew:...
during its final descent. This was due to a switch left in the wrong position, which allowed NTO fumes to vent out of the Apollo spacecraft then back in through the cabin air intake from the outside air after the external vents were opened. One crewmember lost consciousness during descent. Upon landing, the crew was hospitalized 14 days for chemical-induced pneumonia
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
and edema
Edema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
.
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. "Cool" nitrogen 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 cycleBrayton cycle
The Brayton cycle is a thermodynamic cycle that describes the workings of the gas turbine engine, basis of the airbreathing jet engine and others. It is named after George Brayton , the American engineer who developed it, although it was originally proposed and patented by Englishman John Barber...
s have the potential to considerably increase efficiencies of power conversion equipment.
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 acidNitrous acid
Nitrous acid is a weak and monobasic acid known only in solution and in the form of nitrite salts.Nitrous acid is used to make diazides from amines; this occurs by nucleophilic attack of the amine onto the nitrite, reprotonation by the surrounding solvent, and double-elimination of water...
and nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
:
- N2O4 + H2O → HNO2 + HNO3
The coproduct HNO2 upon heating disproportionate
Disproportionation
Disproportionation, also known as dismutation is used to describe a specific type of redox reaction in which a species is simultaneously reduced and oxidized so as to form two different products....
s to NO
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
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, obviously) can be returned to the cycle to give the mixture of nitrous and nitric acids again.
Synthesis of metal nitrates
N2O4 behaves as the salt [NO+][NO3−], the former being a strong oxidant:- 2 N2O4 + M → 2 NO + M(NO3)2
where M = Cu
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, Zn
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, or Sn
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
.
If metal nitrates are prepared from NTO 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 hydrated nitrate 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 degrees C. Many of the anhydrous transition metal nitrates have striking colours. This branch of chemistry was developed by Clifford Addisson and Noramn Logan at Nottingham University in the UK during the 1960s and 1970s when highly efficient desiccants and dry boxes started to become available.