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 N₂O₃. It is one of the simple nitrogen oxides. It forms upon mixing equal parts of nitric oxide 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 + 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. 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 N₂O₃ molecule is planar and exhibits Cs symmetry. The dimensions displayed below come from microwave spectroscopy of low-temperature, gaseous N₂O₃: 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 ...

(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.

References

External links

National Pollutant Inventory – Oxides of nitrogen fact sheet

{{Oxides Nitrogen oxides Acidic oxides Acid anhydrides Sesquioxides