Dinitrogen trioxide
Dinitrogen trioxide
Dinitrogen trioxide is blue
IUPAC name
Other names
Nitrous anhydride, nitrogen sesquioxide
3D model (JSmol)
ECHA InfoCard 100.031.013 Edit this at Wikidata
EC Number
  • 234-128-5
UN number 2421
  • InChI=1S/N2O3/c3-1-2(4)5 checkY
  • InChI=1/N2O3/c3-1-2(4)5
  • [O-][N+](=O)N=O
Molar mass 76.01 g/mol
Appearance deep blue tinted liquid
Density 1.447 g/cm3, liquid
1.783 g/cm3 (gas)
Melting point −100.7[2] °C (−149.3 °F; 172.5 K)
Boiling point 3.5 °C (38.3 °F; 276.6 K)(dissociates[2])
very soluble
Solubility soluble in ether
−16.0·10−6 cm3/mol
planar, Cs
2.122 D
65.3 J/mol K
314.63 J K−1 mol−1
+91.20 kJ/mol
GHS labelling:[3]
GHS03: Oxidizing
GHS04: Compressed Gas
GHS05: Corrosive
GHS06: Toxic
H270, H280, H310, H310+H330, H314, H330
P220, P244, P260, P262, P264, P270, P271, P280, P284, P301+P330+P331, P302+P350, P303+P361+P353, P304+P340, P305+P351+P338, P310, P320, P321, P322, P361, P363, P370+P376, P403, P403+P233, P405, P410+P403, P501
NFPA 704 (fire diamond)
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).
☒N verify (what is checkY☒N ?)

Dinitrogen trioxide is the chemical compound with the formula N2O3. It is one of the simple nitrogen oxides. It forms upon mixing equal parts of nitric oxide and nitrogen dioxide and cooling the mixture below −21 °C (−6 °F):[4]

NO + NO2 ⇌ N2O3

Dinitrogen trioxide is only isolable at low temperatures, i.e. in the liquid and solid phases. In liquid and solid states, it has a deep blue color.[2] At higher temperatures the equilibrium favors the constituent gases, with Kdiss = 193 kPa (25 °C).[5]

This compound is sometimes called "nitrogen trioxide", but this name properly refers to another compound, the (uncharged) nitrate radical NO

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 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:[4]

The bond lengths and angles of dinitrogen trioxide.

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

Here the oxidation state of one nitrogen is +3.


  1. ^ "Dinitrogen trioxide".
  2. ^ a b c Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 444. ISBN 978-0-08-037941-8.
  3. ^ "Dinitrogen trioxide". pubchem.ncbi.nlm.nih.gov. Retrieved 23 December 2021.
  4. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 521–22. ISBN 978-0-08-022057-4.
  5. ^ Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN 0-12-352651-5