Dinitrogen trioxide is the
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the
formula N
2O
3. It is one of the simple
nitrogen oxides. It forms upon mixing equal parts of
nitric oxide
Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...
and
nitrogen dioxide
Nitrogen dioxide is a chemical compound with the formula . It is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year for use primarily in the productio ...
and cooling the mixture below −21 °C (−6 °F):
:NO + NO
2 N
2O
3
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.
At higher temperatures the equilibrium favors the constituent gases, with
''K''diss = 193 kPa (25 °C).
This compound is sometimes called "nitrogen trioxide", but this name properly refers to another compound, the (uncharged)
nitrate radical
Trioxidonitrogen(•) or nitrate radical is an oxide of nitrogen with formula , consisting of three oxygen atoms covalently bound to a nitrogen atom. This highly unstable blue compound has not been isolated in pure form, but can be generated and ...
.
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 N
2O
3 molecule is planar and exhibits Cs symmetry. The dimensions displayed below come from microwave spectroscopy of low-temperature, gaseous N
2O
3:
It is the
anhydride
An organic acid anhydride is an acid anhydride that is an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the pa ...
of the unstable
nitrous acid
Nitrous acid (molecular formula ) is a weak and monoprotic acid known only in solution, in the gas phase and in the form of nitrite () salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagent ...
(HNO
2), 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 N
2O
3 to solutions of bases:
:N
2O
3 + 2 NaOH → 2 NaNO
2 + H
2O
Here the oxidation state of one nitrogen is +3.
References
External links
National Pollutant Inventory – Oxides of nitrogen fact sheet
{{Oxides
Nitrogen oxides
Acidic oxides
Acid anhydrides
Sesquioxides