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Dinitrogen pentoxide



Dinitrogen pentoxide
Other names dinitrogen pentoxide
dnpo
Identifiers
CAS number 10102-03-1
Properties
Molecular formula N2O5
Molar mass 108.01 g mol-1
Appearance white solid
Density  ? g cm-3, solid
Melting point

41 °C (under pressure
to suppress sublimation)

Boiling point

decomposes

Solubility in water decomp. to HNO3
Structure
Coordination
geometry
linear at N2O and planar at NO3
Hazards
MSDS External MSDS
Main hazards strong oxidizer, forms strong
acid in contact with water
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 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is an unstable and potentially dangerous oxidizer that once was used as a reagent for nitrations but has largely been superseded by NO2BF4.

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 nonpolar molecule:

N2O5 [NO2+][NO3]

Additional recommended knowledge

Contents

Syntheses and properties

N2O5 was first reported by Deville in 1840, who prepared it by treating AgNO3 with Cl2. A recommended laboratory synthesis entails dehydrating nitric acid (HNO3) with phosphorus(V) oxide:[1]

P4O10 + 12 HNO3 → 4 H3PO4 + 6 N2O5

In the reverse process, N2O5 reacts with water (hydrolyses) to produce nitric acid. Thus, nitrogen 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. [2]

Structure

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

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.[1]

N2O5 Lewis Structure:

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

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

NO2BF4

Replacement of the NO3 portion of N2O5 with BF4 gives NO2BF4 (CAS#13826-86-3). This salt retains the high reactivity of NO2+, but it is thermally stable, decomposing at ca. 180°C (into 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+.

Hazards

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.

References

  1. ^ a b Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  2. ^ "Nitrogen(V) Oxide" in "Inorganic Syntheses" McGraw-Hill, vol. III, pages 78-81, 1950.
  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, volume 124, pages 153-64.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Dinitrogen_pentoxide". A list of authors is available in Wikipedia.
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