Dinitrogen trioxide

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

NO + NO₂ N₂O₃

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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. K_diss = 193 kPa (25 °C).^[1]

Structure and bonding

Dinitrogen trioxide has an unusually long N−N bond at 186 pm. Whereas N−N bonds are more often similar to that in hydrazine (145 pm), some other oxides of nitrogen do possess long N−N bonds, including dinitrogen tetroxide (175 pm). The N₂O₃ molecule is planar and exhibits C_s symmetry. The dimensions displayed below come from microwave spectroscopy of low-temperature, gaseous N₂O₃:

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 NaN₂O₂ + H2O

Nitrogen Trioxide = NO3

References

1. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.