Dinitrogen pentoxide

Dinitrogen pentoxide is the chemical compound with the formula N2O5. Also known as nitrogen pentoxide, N2O5 is one of the binary nitrogen oxides, a family of compounds that only contain nitrogen and oxygen. It is an unstable and potentially dangerous oxidizer that once was used as a reagent when dissolved in chloroform for nitrations but has largely been superseded by NO2BF4 (nitronium tetrafluoroborate).

Dinitrogen pentoxide
IUPAC name
Dinitrogen pentaoxide
Other names
Nitric anhydride
Nitronium nitrate
Nitryl nitrate
Anhydrous nitric acid
3D model (JSmol)
ECHA InfoCard 100.030.227
EC Number
  • 233-264-2
Molar mass 108.01 g/mol
Appearance white solid
Density 1.642 g/cm3 (18 °C)
Melting point 41 °C (106 °F; 314 K) [1]
Boiling point 47 °C (117 °F; 320 K) sublimes
reacts to give HNO3
Solubility soluble in chloroform
negligible in CCl4
35.6·10−6 cm3/mol (aq)
1.39 D
planar, C2v (approx. D2h)
N–O–N ≈ 180°
178.2 JK−1mol−1 (s)
355.6 JK−1mol−1 (g)
−43.1 kJ/mol (s)
+11.3 kJ/mol (g)
114.1 kJ/mol
Main hazards strong oxidizer, forms strong acid in contact with water
NFPA 704 (fire diamond)
Flash point Non-flammable
Related compounds
Nitrous oxide
Nitric oxide
Dinitrogen trioxide
Nitrogen dioxide
Dinitrogen tetroxide
Related compounds
Nitric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

N2O5 is a rare example of a compound that adopts two structures depending on the conditions: most commonly it is a salt, but under some conditions it is a polar molecule:

[ NO2+ ] [ NO3 ] ⇌ N2O5

Syntheses and properties

N2O5 was first reported by Deville in 1840, who prepared it by treating AgNO3 with Cl2.[2][3] A recommended laboratory synthesis entails dehydrating nitric acid (HNO3) with phosphorus(V) oxide:[4]

P4O10 + 12 HNO3 4 H3PO4 + 6 N2O5

In the reverse process, N2O5 reacts with water (hydrolyses) to produce nitric acid. Thus, dinitrogen pentoxide is the anhydride of nitric acid:

N2O5 + H2O 2 HNO3

N2O5 exists as colourless crystals that sublime slightly above room temperature. The salt eventually decomposes at room temperature into NO2 and O2.[5]


Solid N2O5 is a salt, consisting of separated anions and cations. The cation is the linear nitronium ion NO2+ and the anion is the planar nitrate ion NO3. Thus, the solid could be called nitronium nitrate. Both nitrogen centers have oxidation state +5.

The intact molecule O2N–O–NO2 exists in the gas phase (obtained by subliming N2O5) and when the solid is extracted into nonpolar solvents such as CCl4. In the gas phase, the O–N–O angle is 133° and the N–O–N angle is 114°. When gaseous N2O5 is cooled rapidly ("quenched"), one can obtain the metastable molecular form, which exothermically converts to the ionic form above −70 °C.[4]

Reactions and applications

Dinitrogen pentoxide, for example as a solution in chloroform, has been used as a reagent to introduce the NO2 functionality. This nitration reaction is represented as follows:

N2O5 + Ar–H → HNO3 + Ar–NO2

where Ar represents an arene moiety.

For this use, dinitrogen pentoxide has been largely replaced by nitronium tetrafluoroborate [NO
]. This salt retains the high reactivity of NO2+, but it is thermally stable, decomposing at about 180 °C (into NO2F and BF3). The reactivity of the NO2+ can be further enhanced with strong acids that generate the "super-electrophile" HNO22+.

Dinitrogen pentoxide is relevant to the preparation of explosives.[3][6]

In the atmosphere, dinitrogen pentoxide is an important reservoir of the NOx species that are responsible for ozone depletion: its formation provides a null cycle with which NO and NO2 are temporarily held in an unreactive state.[7] Mixing ratios of several ppbv have been observed in polluted regions of the night-time troposphere.[8] Dinitrogen pentoxide has also been observed in the stratosphere[9] at similar levels, the reservoir formation having been postulated in considering the puzzling observations of a sudden drop in stratospheric NO2 levels above 50 °N, the so-called 'Noxon cliff'.

Variations in N2O5 reactivity in aerosols can result in significant losses in tropospheric ozone, hydroxyl radicals, and NOx concentrations.[10] Two important reactions of N2O5 in atmospheric aerosols are: 1) Hydrolysis to form nitric acid[11] and 2) Reaction with halide ions, particularly Cl, to form ClNO2 molecules which may serve as precursors to reactive chlorine atoms in the atmosphere.[12][13]


N2O5 is a strong oxidizer that forms explosive mixtures with organic compounds and ammonium salts. The decomposition of dinitrogen pentoxide produces the highly toxic nitrogen dioxide gas.


  1. Emeleus (1 January 1964). Advances in Inorganic Chemistry. Academic Press. pp. 77–. ISBN 978-0-12-023606-0. Retrieved 20 September 2011.
  2. M.H. Deville (1849). "Note sur la production de l'acide nitrique anhydre". Compt. Rend. 28: 257–260.
  3. Jai Prakash Agrawal (19 April 2010). High Energy Materials: Propellants, Explosives and Pyrotechnics. Wiley-VCH. pp. 117–. ISBN 978-3-527-32610-5. Retrieved 20 September 2011.
  4. Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN 0-12-352651-5
  5. Nitrogen(V) Oxide. Inorganic Syntheses. 3. 1950. pp. 78–81.
  6. Talawar, M. B.; et al. (2005). "Establishment of Process Technology for the Manufacture of Dinitrogen Pentoxide and its Utility for the Synthesis of Most Powerful Explosive of Today—CL-20". Journal of Hazardous Materials. 124 (1–3): 153–64. doi:10.1016/j.jhazmat.2005.04.021. PMID 15979786.
  7. Finlayson-Pitts, Barbara J.; Pitts, James N. (2000). Chemistry of the upper and lower atmosphere : theory, experiments, and applications. San Diego: Academic Press. ISBN 9780080529073. OCLC 162128929.
  8. HaiChao Wang; et al. (2017). "High N2O5 Concentrations Observed in Urban Beijing: Implications of a Large Nitrate Formation Pathway". Environmental Science and Technology Letters. 4 (10): 416–420. doi:10.1021/acs.estlett.7b00341.
  9. C.P. Rinsland; et al. (1989). "Stratospheric N205 profiles at sunrise and sunset from further analysis of the ATMOS/Spacelab 3 solar spectra". Journal of Geophysical Research. 94: 18341–18349. Bibcode:1989JGR....9418341R. doi:10.1029/JD094iD15p18341.
  10. Macintyre, H. L.; Evans, M. J. (2010-08-09). "Sensitivity of a global model to the uptake of N2O5 by tropospheric aerosol". Atmospheric Chemistry and Physics. 10 (15): 7409–7414. doi:10.5194/acp-10-7409-2010. ISSN 1680-7324.
  11. Brown, S. S.; Dibb, J. E.; Stark, H.; Aldener, M.; Vozella, M.; Whitlow, S.; Williams, E. J.; Lerner, B. M.; Jakoubek, R. (2004-04-16). "Nighttime removal of NOx in the summer marine boundary layer". Geophysical Research Letters. 31 (7): n/a. doi:10.1029/2004GL019412. ISSN 1944-8007.
  12. Gerber, R. Benny; Finlayson-Pitts, Barbara J.; Hammerich, Audrey Dell (2015-07-15). "Mechanism for formation of atmospheric Cl atom precursors in the reaction of dinitrogen oxides with HCl/Cl− on aqueous films" (PDF). Physical Chemistry Chemical Physics. 17 (29): 19360–19370. Bibcode:2015PCCP...1719360H. doi:10.1039/C5CP02664D. ISSN 1463-9084. PMID 26140681.
  13. Kelleher, Patrick J.; Menges, Fabian S.; DePalma, Joseph W.; Denton, Joanna K.; Johnson, Mark A.; Weddle, Gary H.; Hirshberg, Barak; Gerber, R. Benny (2017-09-18). "Trapping and Structural Characterization of the XNO2·NO3– (X = Cl, Br, I) Exit Channel Complexes in the Water-Mediated X– + N2O5 Reactions with Cryogenic Vibrational Spectroscopy". The Journal of Physical Chemistry Letters. 8 (19): 4710–4715. doi:10.1021/acs.jpclett.7b02120. ISSN 1948-7185. PMID 28898581.
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