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Dinitrogen pentoxide
General
Systematic name	nitrogen(V) oxide
Other names	dinitrogen pentoxide, dnpo
Molecular formula	N2O5
Molar mass	108.01 g mol−1
Appearance	white solid
CAS number	[10102-03-1]
Properties
Density and phase	? g cm−3, solid
Solubility in water	decomp. to HNO3
in chloroform	soluble
Melting point	41 °C (under pressure to suppress sublimation)
Boiling point	decomposes
Structure
Coordination geometry	linear at NO2 and planar at NO3
Crystal structure	?
Dipole moment	? D
Hazards
MSDS	External MSDS
Main hazards	strong oxidizer, creates strong acid in contact with water
NFPA 704	1 2 2
Flash point	n/a
R/S statement	?
RTECS number	?
Supplementary data page
Structure & properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid
UV-vis data	UV, 204, 213, 258 nm (pi-->pi*) 378 and 384 nm
IR data	IR, 1428, 1266, 1249, 1206, 1044, 822, 750, 546, and 454 cm-1
Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references

Dinitrogen pentoxide is the binary nitrogen oxide N₂O₅, also known as nitrogen pentoxide. This unstable and potentially dangerous oxidizer was once of interest as a reagent for nitrations but it has largely been superseded by NO₂BF₄, which is more stable and effects the same reactions.

N₂O₅ exists as colorless crystals that sublime at 32.4 °C. The salt decomposes at room temperature into NO₂ and O₂. ^[1]

2N₂O₅ -> 4NO₂ + O₂

Contents 1 Syntheses 2 Structure 3 Reactions and applications 4 Chemistry of NO2BF4 5 Hazards 6 References 7 External links

N₂O₅ was first reported by Deville in 1840, who prepared this species by treating AgNO₃ with Cl₂.

The recommended laboratory synthesis entails the dehydration of nitric acid (HNO₃) with phosphorus(V) oxide:^[2]

P₄O₁₀ + 12 HNO₃ ⇌ 4 H₃PO₄ + 6 N₂O₅

The structure of N₂O₅ in the solid state reveals separated, linear NO₂⁺ and planar NO₃⁻ ions. Thus, the solid could be called nitronium nitrate. Both nitrogen centers have oxidation states V.

The intact molecule O₂N-O-NO₂ does exist in the gas phase (obtained by subliming N₂O₅) and when the solid is extracted into the nonpolar solvent CCl₄. In the gas phase, the O-N-O and N-O-N angles are 133° and 114°, respectively. When gaseous N₂O₅ is cooled rapidly ("quenched"), one can obtain the metastable molecular form, which exothermically converts to the ionic form above -70 °C.^{[2] [1]}

N₂O₅ Lewis Structure:

Dinitrogen pentoxide reacts with water to produce nitric acid (HNO₃), as such nitrogen pentoxide is the anhydride of nitric acid.

Dinitrogen pentoxide sometimes used as a source of the NO₂ functionality, often using it as a solution in chloroform:

N₂O₅ + R-H ⇌ HNO₃ + R-NO₂

F⁻ has been reported as a proton acceptor to neutralize the HNO₃ coproduct.

N₂O₅ is of interest for the preparation of explosives.^[3]

The reactive portion of N₂O₅ is the cation NO₂⁺. NO₃⁻ is unreactive kinetically. Thus, when the NO₃⁻ portion of N₂O₅ is replaced with BF₄⁻, the high reactivity of NO₂⁺ is retained. The great advantage of NO₂BF₄ is that it is stable thermally (up to 180 °C where it decomposes to NO₂F and BF₃). NO₂BF₄ has been used to nitrate a variety of organic compounds, especially arenes and heterocycles. Interestingly, the reactivity of the NO₂⁺ can be further enhanced with strong acids that generate the super-electrophile HNO₂²⁺.

N₂O₅ is a strong oxidizer and could form explosive mixtures with organic compounds and ammonium salts. The decomposition of dinitrogen pentoxide produces the highly toxic nitrogen dioxide, signaled by the appearance of its characteristic reddish-brown color.

1. ^ ^{a b} http://www.inchem.org/documents/pims/chemical/pimg017
2. ^ ^{a b} Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001.
3. ^ Talawar, M. B.; Sivabalan, R.; Polke, B. G.; Nair, U. R.; Gore, G. M.; Asthana, S. N. "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, 2005, vol. 124, pages 153-64

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