Dinitrogen pentoxide
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2008-05-03T13:40:14Z
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{{Chembox new
| Name = Dinitrogen pentoxide
| ImageFile = Dinitrogen-pentoxide-3D-balls.png
| ImageSize = 200px
| ImageName = Dinitrogen pentoxide
| OtherNames = dinitrogen pentoxide<br />dnpo
| Section1 = {{Chembox Identifiers
| CASNo = 10102-03-1
| RTECS =
}}
| Section2 = {{Chembox Properties
| Formula = N<sub>2</sub>O<sub>5</sub>
| MolarMass = 108.01 g mol<sup>-1</sup>
| Appearance = white solid
| Density = 2.05 g cm<sup>-3</sup>, solid
| Solubility = decomp. to HNO<sub>3</sub>
| MeltingPt = 41 °C (under pressure<br /> to suppress sublimation)
| BoilingPt = decomposes
}}
| Section3 = {{Chembox Structure
| Coordination = linear at N<sub>2</sub>O and planar at NO<sub>3</sub>
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [[Dinitrogen pentoxide chemdata supplement#Material Safety Data Sheet|External MSDS]]
| MainHazards = strong oxidizer, forms strong<br /> acid in contact with water
}}
}}
'''Dinitrogen pentoxide''' is the [[chemical compound]] with the [[chemical formula|formula]] N<sub>2</sub>O<sub>5</sub>. Also known as nitrogen pentoxide, N<sub>2</sub>O<sub>5</sub> is one of the binary [[nitrogen]] [[oxygen|oxide]]s 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unstable and potentially dangerous oxidizer that once was used as a [[reagent]] for [[nitration]]s but has largely been superseded by NO<sub>2</sub>BF<sub>4</sub> ([[nitronium tetrafluoroborate]]).
N<sub>2</sub>O<sub>5</sub> 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:
:N<sub>2</sub>O<sub>5</sub> {{unicode|⇌}} [NO<sub>2</sub><sup>+</sup>][NO<sub>3</sub><sup>−</sup>]
==Syntheses and properties==
N<sub>2</sub>O<sub>5</sub> was first reported by Deville in 1840, who prepared it by treating AgNO<sub>3</sub> with [[chlorine|Cl<sub>2</sub>]]. A recommended laboratory synthesis entails dehydrating [[nitric acid]] (HNO<sub>3</sub>) with [[Phosphorus pentoxide|phosphorus(V) oxide]]:<ref name=Holl>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.</ref>
:P<sub>4</sub>O<sub>10</sub> + 12 HNO<sub>3</sub> → 4 H<sub>3</sub>PO<sub>4</sub> + 6 N<sub>2</sub>O<sub>5</sub>
In the reverse process, N<sub>2</sub>O<sub>5</sub> reacts with water ([[hydrolysis|hydrolyses]]) to produce nitric acid. Thus, nitrogen pentoxide is the [[anhydride]] of nitric acid:
:N<sub>2</sub>O<sub>5</sub> + H<sub>2</sub>O → 2 HNO<sub>3</sub>
N<sub>2</sub>O<sub>5</sub> exists as colourless crystals that sublime slightly above room temperature. The salt eventually decomposes at room temperature into [[nitrogen dioxide|NO<sub>2</sub>]] and [[oxygen|O<sub>2</sub>]].
<ref>"Nitrogen(V) Oxide" in "Inorganic Syntheses" McGraw-Hill, vol. III, pages 78-81, 1950.</ref>
==Structure==
Solid N<sub>2</sub>O<sub>5</sub></sub> is a [[salt]], consisting of separated anions and cations. The cation is the linear [[nitronium]] ion NO<sub>2</sub><sup>+</sup> and the anion is planar NO<sub>3</sub><sup>−</sup> ions. Thus, the solid could be called [[nitronium]] [[nitrate]]. Both [[nitrogen]] centers have oxidation states V.
The intact molecule O<sub>2</sub>N-O-NO<sub>2</sub> exists in the gas phase (obtained by subliming N<sub>2</sub>O<sub>5</sub></sub>) and when the solid is extracted into nonpolar [[solvent]]s such as [[carbon tetrachloride|CCl<sub>4</sub>]]. In the gas phase, the O-N-O angle is 133° and the N-O-N angle is 114°. When gaseous N<sub>2</sub>O<sub>5</sub></sub> is cooled rapidly ("quenched"), one can obtain the metastable molecular form, which exothermically converts to the ionic form above -70 °C.<ref name=Holl/>
::N<sub>2</sub>O<sub>5</sub> [[Lewis Structure]]:
::[[Image:N2O5.svg|Structure of the (rare) molecular form of dinitrogen pentoxide]]
==Reactions and applications==
Dinitrogen pentoxide, for example as a solution in [[chloroform]], has been used as a reagent to introduce the NO<sub>2</sub> functionality. This [[nitration]] reaction is represented as follows:
::N<sub>2</sub>O<sub>5</sub> + [[arene|Ar]]-H → HNO<sub>3</sub> + Ar-NO<sub>2</sub>
N<sub>2</sub>O<sub>5</sub> is of interest for the preparation of explosives.<ref>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.</ref>
==NO<sub>2</sub>BF<sub>4</sub>==
Replacement of the NO<sub>3</sub><sup>−</sup> portion of N<sub>2</sub>O<sub>5</sub> with BF<sub>4</sub><sup>−</sup> gives NO<sub>2</sub>BF<sub>4</sub> (CAS#13826-86-3). This salt retains the high reactivity of NO<sub>2</sub><sup>+</sup>, but it is thermally stable, decomposing at ca. 180°C (into NO<sub>2</sub>F and BF<sub>3</sub>). NO<sub>2</sub>BF<sub>4</sub> has been used to nitrate a variety of organic compounds, especially arenes and heterocycles. Interestingly, the reactivity of the NO<sub>2</sub><sup>+</sup> can be further enhanced with strong acids that generate the "super-electrophile" HNO<sub>2</sub><sup>2+</sup>.
==Hazards==
N<sub>2</sub>O<sub>5</sub> 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==
<references/>
[[Category:Oxides]]
[[Category:Nitrogen compounds]]
[[Category:Acidic oxides]]
[[cs:Oxid dusičný]]
[[da:Dinitrogenpentoxid]]
[[de:Distickstoffpentoxid]]
[[es:Óxido de nitrógeno (V)]]
[[it:Pentossido di diazoto]]
[[ja:五酸化二窒素]]
[[pl:Tlenek azotu(V)]]
[[ru:Оксид азота(V)]]
[[zh:五氧化二氮]]