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Dinitrogen trioxide
Other names	Nitrous anhydride
Identifiers
CAS number	10544-73-7
PubChem	61526
Properties
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
Structure
Molecular shape	planar, Cs
Thermochemistry
Std enthalpy of; formation ΔfHo298	+91.20 kJ/mol
Standard molar; entropy So298	314.63 J K−1 mol−1
Hazards
EU Index	Not listed
NFPA 704	0 3 0 OX
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
	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 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

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 K_diss = 193 kPa (25 °C).^[2]

[edit] 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:^[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

[edit] References

^ ^a ^b Greenwood, Norman N.; Earnshaw, A. (1984), Chemistry of the Elements, Oxford: Pergamon, pp. 521–22, ISBN 0-08-022057-6
^ Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5

[edit] External links

[G.26E-0] Greenwood, Norman N.; Earnshaw, A. (1984), Chemistry of the Elements, Oxford: Pergamon, pp. 521–22, ISBN 0-08-022057-6

[1] Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5

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