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Nitrogen trioxide

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Subject: List of UN numbers 2401 to 2500, Dinitrogen trioxide
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Nitrogen trioxide

Dinitrogen trioxide
CAS number 10544-73-7 YesY
PubChem 61526
ChemSpider 55446 YesY
ChEBI CHEBI:29799 YesY
Jmol-3D images Image 1
Molecular formula N2O3
Molar mass 76.01 g/mol
Appearance deep blue liquid
Density 1.4 g/cm3, liquid
1.783 g/cm3 (gas)
Melting point

−100.1 °C (173.05 K)

Boiling point

3 °C (276 K)

Solubility in water very soluble
Molecular shape planar, Cs
Std enthalpy of
+91.20 kJ/mol
Standard molar
314.63 J K−1 mol−1
EU Index Not listed
EU classification Highly toxic (T+)
NFPA 704
Flash point Non-flammable
Related compounds
Related nitrogen oxides Nitrous oxide
Nitric oxide
Nitrogen dioxide
Dinitrogen tetroxide
Dinitrogen pentoxide
Nitrogen trioxide
Related compounds Nitrous acid
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Dinitrogen trioxide is the chemical compound with the formula N2O3. This deep blue liquid 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):[1]

NO + NO2 is in equilibrium with 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).[2]

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:[1]

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


External links

  • National Pollutant Inventory - Oxides of nitrogen fact sheet
  • Webelements: Compound data - dinitrogen trioxide
  • Oxides of nitrogen - synthesis and uses
  • Ivtantermo - dinitrogen trioxide table of values
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