N2O4 is dinitrogen tetroxide while NO2 is nitrogen dioxide. Although the chemical formula N2O4 can be obtained by doubling the stoichiometric values of the chemical formula NO2, these two are different chemical compounds with different chemical and physical properties.
What is N2O4?
N2O4 is dinitrogen tetroxide. We commonly call it as nitrogen tetroxide. This compound occurs as a colourless liquid and is a very useful reagent in chemical synthesis processes. This compound can form an equilibrium mixture with nitrogen dioxide. Further, dinitrogen tetroxide is a powerful oxidizing agent that is hypergolic as well. It is hypergolic upon contact with various forms of hydrazine (this makes the mixture of hydrazine and dinitrogen tetroxide a common bipropellant for rockets).
We can consider the dinitrogen tetroxide molecule as two nitro groups that are bonded together. And, this particular reaction forms an equilibrium mixture of dinitrogen tetroxide and nitrogen dioxide. Also, we can observe the dinitrogen tetroxide molecule as a planar molecule having a weak bond between two nitrogen atoms. It is because this chemical bond is significantly longer than the usual N-N chemical bond.
When considering the magnetic properties of this molecule, it is diamagnetic because there are no unpaired electrons on any atom of this molecule. Moreover, this liquid substance is usually colourless, but there can be a yellow colouration as well due to the presence of NO2 depending on the equilibrium that was mentioned above. More importantly, at elevated temperatures, the equilibrium pushes towards NO2 rather than N2O4.
Dinitrogen tetroxide can be produced by the catalytic oxidation of ammonia, where steam is used as a diluent to reduce the combustion temperature. In this reaction process, the first step includes ammonia oxidation into nitric oxide, and the second step is the oxidation of nitric oxide into nitrogen dioxide, followed by dimerization into nitrogen tetroxide.
What is NO2?
NO2 is nitrogen dioxide. It is one of the several nitrogen oxides. We can observe it as an intermediate in the industrial synthesis of nitric acid, which is important in fertilizer production. Furthermore, NO2 is a brown gas having a chlorine-like odour. When added to water, this compound undergoes hydrolysis. However, this gaseous substance converts into a yellowish-brown liquid at low temperatures. And, this colour change occurs due to the conversion of NO2 into N2O4.
Characteristically, the nitrogen atom of the NO2 molecule has one unpaired electron while there are two N=O bonds in the molecule. Therefore, this compound is paramagnetic; meaning, it can get attracted to an external magnetic field. Furthermore, this single unpaired electron also means that it is a free radical compound.
When considering the preparation of NO2 substance, it typically forms via the oxidation of nitric oxide by oxygen in the air. Also, this substance forms in most combustion processes using air as the oxidizing agent.
There are few different uses of NO2, including the use of it as an intermediate in the manufacturing of nitric acid, as a nitrating agent in the manufacture of chemical explosives, as a polymerization inhibitor for acrylates, as a flour bleaching agent, etc.
What is the Difference Between N2O4 and NO2?
N2O4 is dinitrogen tetroxide while NO2 is nitrogen dioxide. The key difference between N2O4 and NO2 is that N2O4 is diamagnetic, whereas NO2 is paramagnetic. Further, N2O4 occurs as a liquid, while NO2 is a gaseous substance. Moreover, N2O4 is a colourless liquid while NO2 is a brown gas.
The following info-graphic tabulates more differences between N2O4 and NO2 for side by side comparison.
Summary – N2O4 vs NO2
N2O4 is dinitrogen tetroxide. NO2 is nitrogen dioxide. When considering the chemical properties of these two compounds, magnetic properties are very important. The key difference between N2O4 and NO2 is that N2O4 is diamagnetic, whereas NO2 is paramagnetic. Diamagnetic means the N2O4 molecules are not attracted to an external magnetic field because there are no unpaired electrons in this molecule. Paramagnetic means the molecule is attracted to an external magnetic field because there is an unpaired electron in the NO2 molecule.
1. “Dinitrogen tetroxide.” Pubchem, Available here.