Dinitrogen pentoxide
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| Dinitrogen pentoxide | |
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| IUPAC name |
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| Other names | Nitric anhydride dnpo |
| Identifiers | |
| CAS number | [] |
| PubChem | |
| Properties | |
| Molecular formula | N2O5 |
| Molar mass | 108.01 g/mol |
| Appearance | white solid |
| Density | 1.642 g/cm3 (18 °C) |
| Melting point |
30 |
| Boiling point |
47 ºC subl. |
| 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 ΔfH |
−43.1 kJ/mol (s) +11.3 kJ/mol (g) |
| Standard molar entropy S |
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 |
 0
3
0
OX
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| 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, 100 kPa) Infobox references |
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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is an unstable and potentially dangerous oxidizer that once was used as a reagent for nitrations but has largely been superseded by NO2BF4 (nitronium tetrafluoroborate).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 nonpolar molecule:
- N2O5 ⇌ [NO2+][NO3−]
Contents |
[edit] Syntheses and properties
N2O5 was first reported by Deville in 1840, who prepared it by treating AgNO3 with Cl2. A recommended laboratory synthesis entails dehydrating nitric acid (HNO3) with phosphorus(V) oxide:[1]
- 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. [2]
[edit] Structure
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 NO3− ion. 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.[1]
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- N2O5 Lewis Structure:
[edit] 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:
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- N2O5 + Ar-H → HNO3 + Ar-NO2
N2O5 is of interest for the preparation of explosives.[3]
[edit] 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+.
[edit] 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.
[edit] References
- ^ a b Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5
- ^ "Nitrogen(V) Oxide", Inorg. Synth. 3: 78–81, 1950
- ^ 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.
