Dinitrogen Tetroxide N2O4

Dinitrogen tetroxide is a colourless solid existing in equilibrium with nitrogen dioxide of brown colour. This mixture of NO2 and colourless N2O4 produces poisonous brown colored vapours. This poisonous gas is not safe to store in cylinders and ton containers if they are not equipped with a safety relief device. Long exposure of the containers to fire or heat will result in rupture and hazardous rupturing and rocketing. 

Dinitrogen tetroxide is mainly considered as two nitro groups (-NO2) that are bonded together. This bond forms an equilibrium mixture with nitrogen dioxide. The molecule formed through the equilibrium of nitrogen dioxide and dinitrogen tetroxide is planar with an N-N bond distance of about 1.78 Å and N-O distances of about 1.19 Å. 

However, between these distances, the N-N distance seems to be a weak bond, since it is much longer than the average N-N single bond length of 1.45 Å. This case of exceptionally weak σ bond joining to the overlapping of the sp2 hybrid orbitals present in the two NO2 units of results from the simultaneous delocalization of the electron bond pair that are placed all across the whole N2O4 or dinitrogen tetroxide molecule, and we also consider the usual electrostatic repulsion of the doubly occupied by the orbitals present in the molecules of each NO2 unit. 

However, Unlike NO2 nitrogen dioxide, dinitrogen tetroxide N2O4 is diamagnetic since it possesses no unpaired electrons on its own. The liquid formed is also colourless but sometimes it appears as a light brownish yellow liquid because of the presence of nitrogen dioxide NO2 according to the following equilibrium stated below:

N2O4 ⇌ 2 NO2

Production Of Dinitrogen Tetroxide

As we know from our earlier knowledge about Nitrogen tetroxide, Nitrogen tetroxide is made by the use of catalytic oxidation of ammonia: the use of steam is used as a medium to reduce the combustion temperature. However,  In the initial step, the ammonia is first oxidised into nitric oxide: the following is the equation for the process

4 NH3 + 5 O2 → 4 NO + 6 H2O

Then when Most of the water is condensed out and even the gases are further cooled down; the nitric oxide that was earlier produced is then oxidised to nitrogen dioxide, which is then transformed into nitrogen tetroxide: the equation showing the process

2 NO + O2 → 2 NO2

2 NO2 ⇌ N2O4

This process results in the statement Dinitrogen tetroxide is a colourless solid existing in equilibrium with nitrogen dioxide and the rest of the water is removed as a form of nitric acid. The gas remaining is essentially pure nitrogen dioxide, which is then turned into dinitrogen tetroxide by condensing in a brine-cooled liquefier. Dinitrogen tetroxide can also be made with the help of a reaction of concentrated nitric acid and metallic copper. 

Dinitrogen Tetroxide is Used as Rocket Propellant

As it is a powerful oxidizer, dinitrogen tetroxide is vastly used as an oxidising agent in one of the most important rocket propellants because due to its properties dinitrogen tetroxide can be stored as a form of liquid at room temperature. 

In 1927 Pedro Paulet, a Peruvian polymath reported that he had experimented with a rocket engine in the 1890s where he utilised spring-loaded nozzles that helped is introducing vaporised nitrogen tetroxide and petroleum benzine to form a spark plug for ignition, when the engine putting was out at 300 pulsating explosions per minute, Paulet periodically would go on to visit the German rocket association Verein für Raumschiffahrt (VfR) for his interest and on March 15, 1928, Valier finally was and applauded the idea of Paulet’s liquid-propelled rocket design in the VfR publication Die Rakete.

When nitrogen tetroxide was used as a propellant, dinitrogen tetroxide was usually referred to in simple terms as nitrogen tetroxide and there was extensive use of the abbreviation NTO. Whenever NTO was used it was often used with a small percentage of addition of nitric oxide, which helps in inhibiting the stress-corrosion or cracking of titanium alloys, propellant-grade NTO was mainly referred to as mixed oxides of nitrogen (MON) in this form. 

In recent years the majority of spacecraft now use the term MON instead of NTO; for example, the Space Shuttle reaction control system used MON3 which contained  3% NTO and NO by weight.

Generating Power Using Dinitrogen Tetroxide N2O4

Dinitrogen tetroxide or N2O4 always keeps a tendency to reversibly break into NO2, which has led to research into its huge use in advanced power generation systems which are mainly so-called dissociating gas. “Cool” dinitrogen tetroxide is then compressed and again heated, which causes the nitrogen tetroxide to dissociate again into nitrogen dioxide at half of its molecular weight. 

This compressed and hot nitrogen dioxide is then expanded with the help of a turbine, causing it to cool down and lower the pressure, and then again repeating the same purpose of cooling it further in a heat sink, causing it to combine again into nitrogen tetroxide at its original molecular weight. Then the whole process gets much easier to compress and repeat the entire cycle. Hence, it is also used as a reagent in the synthesis of many chemical compounds.

Conclusion

Nitrogen dioxide is pushed towards equilibrium in comparatively higher temperatures. But in some cases, dinitrogen tetroxide is a component formed of smog containing nitrogen dioxide.

Dinitrogen tetroxide is known for many years for its ability to react with metals, such as lithium amongst the alkali metals and calcium, under pretty mild conditions as it is a powerful oxidizer. This is why such type reactions are recognized to initially showcase those tarnishing reactions, but in these reactions, the ultimate bulk product is the metal nitride, for example, Li3N. 

The very first step in such reactions is a transfer of an electron from a particular metal, which is highly reduced in nature, and then transfer it to the dinitrogen to form N2.