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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is an unstable and potentially dangerous oxidizer that once was used as a reagent for nitrations but has largely been superseded by NO2BF4.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:
Additional recommended knowledge
Syntheses and properties
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.
Reactions and applications
N2O5 is of interest for the preparation of explosives.
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+.
|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.