Dinitrogen trioxide

Dinitrogen trioxide
Other names
Nitrous anhydride, nitrogen sesquioxide
10544-73-7 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:29799 YesY
ChemSpider 55446 YesY
ECHA InfoCard 100.031.013
EC Number 234-128-5
PubChem 61526
UNII 16E0524PXI YesY
Molar mass 76.01 g/mol
Appearance deep blue liquid
Density 1.447 g/cm3, liquid
1.783 g/cm3 (gas)
Melting point −100.7[1] °C (−149.3 °F; 172.5 K)
Boiling point 3.5 °C (38.3 °F; 276.6 K)(dissociates[1])
very soluble
Solubility soluble in ether
planar, Cs
2.122 D
65.3 J/mol K
314.63 JK1mol1
+91.20 kJ/mol
Highly toxic (T+)
NFPA 704
Flash point Non-flammable
Related compounds
Nitrous oxide
Nitric oxide
Nitrogen dioxide
Dinitrogen tetroxide
Dinitrogen pentoxide
Nitrogen trioxide
Related compounds
Nitrous acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Dinitrogen trioxide is the chemical compound with the formula N2O3. This deep blue solid[1] is one of the binary nitrogen oxides. It forms upon mixing equal parts of nitric oxide and nitrogen dioxide and cooling the mixture below 21 °C (6 °F):[2]

NO + NO2 N2O3

Dinitrogen trioxide is only isolable at low temperatures, i.e. in the liquid and solid phases. At higher temperatures the equilibrium favors the constituent gases, with Kdiss = 193 kPa (25 °C).[3]

Structure and bonding

Typically, N–N bonds are similar in length to that in hydrazine (145 pm). Dinitrogen trioxide, however, has an unusually long N–N bond at 186 pm. Some other nitrogen oxides do also possess long N–N bonds, including dinitrogen tetroxide (175 pm). The N2O3 molecule is planar and exhibits Cs symmetry. The dimensions displayed below come from microwave spectroscopy of low-temperature, gaseous N2O3:[2]

It is the anhydride of the unstable nitrous acid (HNO2), and produces it when mixed into water. An alternative structure might be anticipated for the true anhydride, i.e. O=N–O–N=O, but this isomer is not observed. If the nitrous acid is not then used up quickly, it decomposes into nitric oxide and nitric acid. Nitrite salts are sometimes produced by adding N2O3 to solutions of bases:

N2O3 + 2 NaOH → 2 NaNO2 + H2O


  1. 1 2 3 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 444. ISBN 0-08-037941-9.
  2. 1 2 Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 521–22. ISBN 0-08-022057-6.
  3. Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5
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