Everything about Dinitrogen Pentoxide totally explained
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Dinitrogen pentoxide is the
chemical compound with the
formula N
2O
5. Also known as nitrogen pentoxide, N
2O
5 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nitrations but has largely been superseded by NO
2BF
4 (
nitronium tetrafluoroborate).
N
2O
5 is a rare example of a compound that adopts two structures depending on the conditions: most commonly it's a salt, but under some conditions it's a nonpolar molecule:
» N
2O
5 ⇌ [NO
2+][NO
3−]
Syntheses and properties
N
2O
5 was first reported by Deville in 1840, who prepared it by treating AgNO
3 with
Cl2. A recommended laboratory synthesis entails dehydrating
nitric acid (HNO
3) with
phosphorus(V) oxide:
» P
4O
10 + 12 HNO
3 → 4 H
3PO
4 + 6 N
2O
5
In the reverse process, N
2O
5 reacts with water (
hydrolyses) to produce nitric acid. Thus, nitrogen pentoxide is the
anhydride of nitric acid:
» N
2O
5 + H
2O → 2 HNO
3
N
2O
5 exists as colourless crystals that sublime slightly above room temperature. The salt eventually decomposes at room temperature into
NO2 and
O2.
Structure
Solid N
2O
5 is a
salt, consisting of separated anions and cations. The cation is the linear
nitronium ion NO
2+ and the anion is planar NO
3− ions. Thus, the solid could be called
nitronium nitrate. Both
nitrogen centers have oxidation states V.
The intact molecule O
2N-O-NO
2 exists in the gas phase (obtained by subliming N
2O
5) 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 N
2O
5 is cooled rapidly ("quenched"), one can obtain the metastable molecular form, which exothermically converts to the ionic form above -70 °C.
NO2BF4
Replacement of the NO
3− portion of N
2O
5 with BF
4− gives NO
2BF
4 (CAS#13826-86-3). This salt retains the high reactivity of NO
2+, but it's thermally stable, decomposing at ca. 180°C (into NO
2F and BF
3). NO
2BF
4 has been used to nitrate a variety of organic compounds, especially arenes and heterocycles. Interestingly, the reactivity of the NO
2+ can be further enhanced with strong acids that generate the "super-electrophile" HNO
22+.
Hazards
N
2O
5 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.
Further Information
Get more info on 'Dinitrogen Pentoxide'.
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