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What is Nitrogen Sesquioxide?

Last updated date: 24th Feb 2024
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Nitrogen Sesquioxide: An Introduction

Nitrogen Sesquioxide is one of the oxides of nitrogen, its chemical name is dinitrogen trioxide. The chemical formula of nitrogen sesquioxide is N2O3. It appears as a blue liquid and has a distinctly unpleasant odour. It is obtained at a very low temperature at around -30oC by condensing equal parts of NO (nitric oxide) and NO2 (nitrogen dioxide). At a higher temperature above -30oC, it partially dissociates into NO and NO2. At a very low temperature (~ -100 oC), N2O3 can be isolated in the solid phase, it condenses as a pale blue solid.

The liquid N2O3 undergoes self-ionization to form nitrosonium ion (NO+):

N2O3 ⇌ NO+ + NO2-

It is a strong oxidizing agent and is highly corrosive in nature. It comes under the category of hazardous chemicals and can be extremely harmful, and potentially fatal if inhaled. Contact with soft surfaces like skin, eyes, or mucous membranes can cause strong irritation.

Physical Properties

The compound, N2O3, is highly unstable as it dissociates at higher temperatures. This makes it difficult to predict the physical properties accurately.

Table: Properties of N2O3

Molecular Formula


Boiling Point

3.5 oC

Melting Point

-100.7 oC


1.4 g/ cm3 (liquid)

1.783 g/ cm3 (gas)

Molecular Weight

76.012 g mol-1

N2O3 Structure

The N2O3 molecule has two nitrogen atoms bound with a single bond; they form the centre of the molecule. One of the nitrogen is connected to two oxygen atoms through a single bond and a double bond; the second nitrogen has one doubly bonded oxygen atom.

N2O3 structure

N2O3 Structure

Spectral studies have revealed the geometry. of nitrogen sesquioxide as planar in both solid as well as other states.

Bond lengths and Bond <a href=''>angles</a> of Dinitrogen trioxide

Bond Lengths and Bond Angles of Dinitrogen Trioxide

The N—N bond in dinitrogen trioxide is rather long (1.86Ao) when compared with the bond length of hydrazine NH2—NH2 (1.45Ao). The compound is diamagnetic in nature indicating the absence of odd electrons.

Another proposed structure of N2O3 in the complete anhydrous condition is assumed as shown below, it is also thought to take such a shape upon irradiation by light of appropriate wavelength. Although it was not right.

Proposed structure of anhydrous N2O3

Proposed Structure of Anhydrous N2O3


The most common method of preparation of N2O3 is by condensing equimolar NO and NO2 at very low temperatures. NO2 can be produced in situ by adding an appropriate amount of O2 to NO.

2NO + N2O4 → 2N2O3 (in cold condition)

4NO + O2 → 2N2O3

N2O3 can also be prepared by reducing nitric acid (1:1) by As2O3 (at 70oC).

2HNO3 + 2 H2O + As2O3 → N2O3 + 2H3AsO4

However, the drawback of the above method is that product yields are not completely anhydrous, due to the presence of water in the reaction. Dehydration of the product is difficult in this condition.

Chemical Reactions

N2O3 is an acidic oxide, it is the anhydride form of nitrous acid (HNO2). In the presence of water, it forms nitrous acid.

N2O3 + H2O ⇌ 2HNO2

In alkaline solution, it is converted to nitrites. For example, dinitrogen trioxide reacts with sodium hydroxide to give sodium nitrite (NaNO2)

N2O3 + 2NaOH ⇌ 2NaNO2 + H2O

Uses of N2O3

  • It is one of the sources of nitrosonium ion NO+ that has extensive chemistry.

  • In the organic synthesis of proton and water-sensitive products that involve nitrosation and nitration of the substrate, nitric acid is replaced by solvent-stabilized dinitrogen trioxide (readily prepared in high concentrations in dry organic solvent at the normal working condition). This allows acid and water-free reaction conditions.

  • N2O3 is used as special-purpose rocket fuel due to its combustible nature. However, exposure to heat for a long time may rupture the container and the rocket violently. Due to its strong oxidizing ability, it is used as an oxidizing agent.

Key Features

  • N2O3 compound name is nitrogen sesquioxide

  • N2O3 chemical name is Dinitrogen trioxide

  • N2O3 is one of the simplest oxides of nitrogen

  • N2O3 is a strongly oxidizing agent. It is highly corrosive and hazardous.

  • N2O3 is used as special fuel in rocket engines.

  • N2O3 forms the part of simple nitrogen oxides (NOx) formed in the internal combustion of engines due to the combustion of fossil fuel. It contributes to air pollution from vehicular emissions.

  • Like other oxides of nitrogen, dinitrogen trioxide is found in nature as a part of the biogeochemical cycle of nitrogen on earth.

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FAQs on What is Nitrogen Sesquioxide?

1. What is sesquioxide?

Sesquioxide is an oxide of an element or radical, that contains three atoms of oxygen, and two atoms of the element or the radical. It maintains a ratio of 2:3 between the number of elements and the oxygen atoms. Some examples of sesquioxide other than N2O3 are Al2O3, P4O6, and Fe2O3.  

2. What type of bond does N2O3 have?

N2O3 has covalent bonds. In the molecule, electron pairs are shared between the nitrogen atoms and the oxygen atoms, which is the characteristic of covalent bonds. The bonds are formed by sharing of electrons between nitrogen atoms and oxygen atoms. One out of two nitrogen atoms also donates lone pair electrons to one oxygen atom.

3. What is the oxidation state of nitrogen in nitrogen sesquioxide?

The oxidation state of nitrogen in nitrogen sesquioxide (N2O3) is +3. Most sesquioxide contains elements or metals in the +3 oxidation state and oxygen in the -2 state.