Dinitrogen pentoxide


Dinitrogen pentoxide
Dinitrogen pentoxide
Identifiers
CAS number 10102-03-1 YesY
PubChem 66242
ChemSpider 59627 YesY
ChEBI CHEBI:29802 YesY
Jmol-3D images Image 1
Properties
Molecular formula N2O5
Molar mass 108.01 g/mol
Appearance white solid
Density 1.642 g/cm3 (18 °C)
Melting point

41 °C[1]

Boiling point

47 °C (sublimates)

Solubility in water reacts to give HNO3
Solubility soluble in chloroform
Structure
Molecular shape planar, C2v (approx. D2h)
N–O–N ≈ 180º
Thermochemistry
Std enthalpy of
formation
ΔfHo298
−43.1 kJ/mol (s)
+11.3 kJ/mol (g)
Standard molar
entropy
So298
178.2 J K−1 mol−1 (s)
355.6 J K−1 mol−1 (g)
Hazards
EU Index Not listed
Main hazards strong oxidizer, forms strong acid in contact with water
NFPA 704
NFPA 704.svg
0
3
0
OX
Flash point Non-flammable
Related compounds
Related nitrogen oxides Nitrous oxide
Nitric oxide
Dinitrogen trioxide
Nitrogen dioxide
Dinitrogen tetroxide
Related compounds Nitric acid
 YesY pentoxide (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox 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dangerous oxidizer that once was used as a reagent when dissolved in chloroform for nitrations but has largely been superseded by NO2BF4 (nitronium tetrafluoroborate).

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:

N2O5 [NO2+][NO3]

Contents

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, 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. [5]

Structure

Lewis structure of gas-phase N2O5

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 NO3 ion. 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.

N2O5 is of interest for the preparation of explosives.[3][6]

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. ^ Emeleus (1 January 1964). Advances in Inorganic Chemistry. Academic Press. pp. 77–. ISBN 978-0-12-023606-0. http://books.google.com/books?id=UPBKxgY20lEC&pg=PA77. Retrieved 20 September 2011. 
  2. ^ M.H. Deville (1849). "Note sur la production de l'acide nitrique anhydre". Compt. Rend. Acad. Sci. Paris 28: 257–260. http://www.archive.org/details/comptesrendusheb28acad. 
  3. ^ a b Jai Prakash Agrawal (19 April 2010). High Energy Materials: Propellants, Explosives and Pyrotechnics. Wiley-VCH. pp. 117–. ISBN 978-3-527-32610-5. http://books.google.com/books?id=rqZROysoS7QC&pg=PA117. Retrieved 20 September 2011. 
  4. ^ a b Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, 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: 153–64. doi:10.1016/j.jhazmat.2005.04.021. 

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