Английская Википедия:Dinitrogen pentoxide
Шаблон:Chembox Dinitrogen pentoxide (also known as nitrogen pentoxide or nitric anhydride) is the chemical compound with the formula Шаблон:Chem2. It is one of the binary nitrogen oxides, a family of compounds that only contain nitrogen and oxygen. It exists as colourless crystals that sublime slightly above room temperature, yielding a colorless gas.[1]
Dinitrogen pentoxide 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dangerous oxidizer that once was used as a reagent when dissolved in chloroform for nitrations but has largely been superseded by nitronium tetrafluoroborate (Шаблон:Chem2).
Шаблон:Chem2 is a rare example of a compound that adopts two structures depending on the conditions. The solid is a salt, nitronium nitrate, consisting of separate nitronium cations Шаблон:Chem2 and nitrate anions Шаблон:Chem2; but in the gas phase and under some other conditions it is a covalently-bound molecule.[2]
History
Шаблон:Chem2 was first reported by Deville in 1840, who prepared it by treating silver nitrate (Шаблон:Chem2) with chlorine.[3][4]
Structure and physical properties
Pure solid Шаблон:Chem2 is a salt, consisting of separated linear nitronium ions Шаблон:Chem2 and planar trigonal nitrate anions Шаблон:Chem2. Both nitrogen centers have oxidation state +5. It crystallizes in the space group DШаблон:Su (C6/mmc) with Z = 2, with the Шаблон:Chem2 anions in the D3h sites and the Шаблон:Chem2 cations in D3d sites.[5]
The vapor pressure P (in atm) as a function of temperature T (in kelvin), in the range Шаблон:Cvt, is well approximated by the formula
- <math> \ln P = 23.2348 - \frac{7098.2}{T}</math>
being about 48 torr at 0 °C, 424 torr at 25 °C, and 760 torr at 32 °C (9 °C below the melting point).[6]
In the gas phase, or when dissolved in nonpolar solvents such as carbon tetrachloride, the compound exists as covalently-bonded molecules Шаблон:Chem2. In the gas phase, theoretical calculations for the minimum-energy configuration indicate that the Шаблон:Chem2 angle in each Шаблон:Chem2 wing is about 134° and the Шаблон:Chem2 angle is about 112°. In that configuration, the two Шаблон:Chem2 groups are rotated about 35° around the bonds to the central oxygen, away from the Шаблон:Chem2 plane. The molecule thus has a propeller shape, with one axis of 180° rotational symmetry (C2) [7]
When gaseous Шаблон:Chem2 is cooled rapidly ("quenched"), one can obtain the metastable molecular form, which exothermically converts to the ionic form above −70 °C.[8]
Gaseous Шаблон:Chem2 absorbs ultraviolet light with dissociation into the free radicals nitrogen dioxide Шаблон:Chem2 and nitrogen trioxide Шаблон:Chem2 (uncharged nitrate). The absorption spectrum has a broad band with maximum at wavelength 160 nm.[9]
Preparation
A recommended laboratory synthesis entails dehydrating nitric acid (Шаблон:Chem2) with phosphorus(V) oxide:[8]
Another laboratory process is the reaction of lithium nitrate Шаблон:Chem2 and bromine pentafluoride Шаблон:Chem2, in the ratio exceeding 3:1. The reaction first forms nitryl fluoride Шаблон:Chem2 that reacts further with the lithium nitrate:[5]
The compound can also be created in the gas phase by reacting nitrogen dioxide Шаблон:Chem2 or Шаблон:Chem2 with ozone:[10]
However, the product catalyzes the rapid decomposition of ozone:[10]
Dinitrogen pentoxide is also formed when a mixture of oxygen and nitrogen is passed through an electric discharge.[5] Another route is the reactions of Phosphoryl chloride Шаблон:Chem2 or nitryl chloride Шаблон:Chem2 with silver nitrate Шаблон:Chem2[5][11]
Reactions
Dinitrogen pentoxide reacts with water (hydrolyses) to produce nitric acid Шаблон:Chem2. Thus, dinitrogen pentoxide is the anhydride of nitric acid:[8]
Solutions of dinitrogen pentoxide in nitric acid can be seen as nitric acid with more than 100% concentration. The phase diagram of the system Шаблон:Chem2−Шаблон:Chem2 shows the well-known negative azeotrope at 60% Шаблон:Chem2 (that is, 70% Шаблон:Chem2), a positive azeotrope at 85.7% Шаблон:Chem2 (100% Шаблон:Chem2), and another negative one at 87.5% Шаблон:Chem2 ("102% Шаблон:Chem2").[12]
The reaction with hydrogen chloride Шаблон:Chem2 also gives nitric acid and nitryl chloride Шаблон:Chem2:[13]
Dinitrogen pentoxide eventually decomposes at room temperature into [[nitrogen dioxide|Шаблон:Chem2]] and [[oxygen|Шаблон:Chem2]].[14][10] Decomposition is negligible if the solid is kept at 0 °C, in suitably inert containers.[5]
Dinitrogen pentoxide reacts with ammonia Шаблон:Chem2 to give several products, including nitrous oxide Шаблон:Chem2, ammonium nitrate Шаблон:Chem2, nitramide Шаблон:Chem2 and ammonium dinitramide Шаблон:Chem2, depending on reaction conditions.[15]
Decomposition of dinitrogen pentoxide at high temperatures
Dinitrogen pentoxide between high temperatures of Шаблон:Cvt, is decomposed in two successive stoichiometric steps:
In the shock wave, Шаблон:Chem2 has decomposed stoichiometrically into nitrogen dioxide and oxygen. At temperatures of 600 K and higher, nitrogen dioxide is unstable with respect to nitrogen oxide Шаблон:Chem and oxygen. The thermal decomposition of 0.1 mM nitrogen dioxide at 1000 K is known to require about two seconds.[16]
Decomposition of dinitrogen pentoxide in carbon tetrachloride at 30 °C
Apart from the decomposition of Шаблон:Chem2 at high temperatures, it can also be decomposed in carbon tetrachloride Шаблон:Chem2 at Шаблон:Cvt.[17] Both Шаблон:Chem2 and Шаблон:Chem2 are soluble in Шаблон:Chem2 and remain in solution while oxygen is insoluble and escapes. The volume of the oxygen formed in the reaction can be measured in a gas burette. After this step we can proceed with the decomposition, measuring the quantity of Шаблон:Chem2 that is produced over time because the only form to obtain Шаблон:Chem2 is with the Шаблон:Chem2 decomposition. The equation below refers to the decomposition of Шаблон:Chem2 in Шаблон:Chem2:
And this reaction follows the first order rate law that says:
- <math>-\frac{d[\mathrm{A}]}{dt} = k [\mathrm{A}]</math>
Decomposition of nitrogen pentoxide in the presence of nitric oxide
Шаблон:Chem2 can also be decomposed in the presence of nitric oxide Шаблон:Chem2:
The rate of the initial reaction between dinitrogen pentoxide and nitric oxide of the elementary unimolecular decomposition.[18]
Applications
Nitration of organic compounds
Dinitrogen pentoxide, for example as a solution in chloroform, has been used as a reagent to introduce the [[Nitro compound|Шаблон:Chem2]] functionality in organic compounds. This nitration reaction is represented as follows:
where Ar represents an arene moiety.[19] The reactivity of the Шаблон:Chem2 can be further enhanced with strong acids that generate the "super-electrophile" Шаблон:Chem2.
In this use, Шаблон:Chem2 has been largely replaced by nitronium tetrafluoroborate Шаблон:Chem2. This salt retains the high reactivity of Шаблон:Chem2, but it is thermally stable, decomposing at about 180 °C (into [[nitryl fluoride|Шаблон:Chem2]] and [[boron trifluoride|Шаблон:Chem2]]).
Dinitrogen pentoxide is relevant to the preparation of explosives.[4][20]
Atmospheric occurrence
In the atmosphere, dinitrogen pentoxide is an important reservoir of the Шаблон:Chem2 species that are responsible for ozone depletion: its formation provides a null cycle with which Шаблон:Chem2 and Шаблон:Chem2 are temporarily held in an unreactive state.[21] Mixing ratios of several parts per billion by volume have been observed in polluted regions of the nighttime troposphere.[22] Dinitrogen pentoxide has also been observed in the stratosphere[23] at similar levels, the reservoir formation having been postulated in considering the puzzling observations of a sudden drop in stratospheric Шаблон:Chem2 levels above 50 °N, the so-called 'Noxon cliff'.
Variations in Шаблон:Chem2 reactivity in aerosols can result in significant losses in tropospheric ozone, hydroxyl radicals, and Шаблон:Chem2 concentrations.[24] Two important reactions of Шаблон:Chem2 in atmospheric aerosols are hydrolysis to form nitric acid[25] and reaction with halide ions, particularly [[chloride|Шаблон:Chem2]], to form [[ClNO2|Шаблон:Chem2]] molecules which may serve as precursors to reactive chlorine atoms in the atmosphere.[26][27]
Hazards
Шаблон:Chem2 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
Cited sources
Шаблон:Oxides Шаблон:Nitrogen compounds Шаблон:Oxygen compounds
- ↑ Connell, Peter Steele. (1979) The Photochemistry of Dinitrogen Pentoxide. Ph. D. thesis, Lawrence Berkeley National Laboratory.
- ↑ Шаблон:Cite journal
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- ↑ 5,0 5,1 5,2 5,3 5,4 Шаблон:Cite journal
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- ↑ 8,0 8,1 8,2 Шаблон:Holleman&Wiberg
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- ↑ 10,0 10,1 10,2 Шаблон:Cite journal
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- ↑ Jaime, R. (2008). Determinación de orden de reacción haciendo uso de integrales definidas. Universidad Nacional Autónoma de Nicaragua, Managua.
- ↑ Шаблон:Cite journal
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