Dinitrogen pentoxide

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Dinitrogen pentoxide
Full structural formula with dimensions
Ball-and-stick model
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 ≈ 180°
Thermochemistry
Std molar
entropy
So298
178.2 J K−1 mol−1 (s)
355.6 J K−1 mol−1 (g)
Std enthalpy of
formation
ΔfHo298
−43.1 kJ/mol (s)
+11.3 kJ/mol (g)
Hazards
EU Index Not listed
Main hazards strong oxidizer, forms strong acid in contact with water
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazard OX: Oxidizer. E.g., potassium perchlorateNFPA 704 four-colored diamond
Flash point Non-flammable
Related compounds
Related nitrogen oxides Nitrous oxide
Nitric oxide
Dinitrogen trioxide
Nitrogen dioxide
Dinitrogen tetroxide
Related compounds Nitric acid
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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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dangerous oxidizer that once was used as a reagent when dissolved in chloroform for nitrations but has largely been superseded by NO2BF4 (nitronium tetrafluoroborate).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]

Syntheses and properties[edit]

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[edit]

Lewis structure of gas-phase N
2
O
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 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[edit]

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]

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.

NO2BF4[edit]

Replacement of the NO3 portion of N2O5 with BF4 gives nitronium tetrafluoroborate (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[edit]

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[edit]

  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. ^ 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. 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.