Dinitrogen trioxide

Dinitrogen trioxide is the chemical compound with the formula N2O3. This deep blue solid[1] is one of the simple nitrogen oxides. It forms upon mixing equal parts of nitric oxide and nitrogen dioxide and cooling the mixture below −21 °C (−6 °F):[2]

NO + NO2 ⇌ N2O3

Dinitrogen trioxide is only isolable at low temperatures, i.e. in the liquid and solid phases. At higher temperatures the equilibrium favors the constituent gases, with Kdiss = 193 kPa (25 °C).[3]

Dinitrogen trioxide
Dinitrogen trioxide
Other names
Nitrous anhydride, nitrogen sesquioxide
3D model (JSmol)
ECHA InfoCard 100.031.013
EC Number 234-128-5
Molar mass 76.01 g/mol
Appearance deep blue tinted gas
Density 1.447 g/cm3, liquid
1.783 g/cm3 (gas)
Melting point −100.7[1] °C (−149.3 °F; 172.5 K)
Boiling point 3.5 °C (38.3 °F; 276.6 K)(dissociates[1])
very soluble
Solubility soluble in ether
−16.0·10−6 cm3/mol
planar, Cs
2.122 D
65.3 J/mol K
314.63 J K−1 mol−1
+91.20 kJ/mol
Highly toxic (T+)
NFPA 704
Flash point Non-flammable
Related compounds
Nitrous oxide
Nitric oxide
Nitrogen dioxide
Dinitrogen tetroxide
Dinitrogen pentoxide
Nitrogen trioxide
Related compounds
Nitrous acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Structure and bonding

Typically, N–N bonds are similar in length to that in hydrazine (145 pm). Dinitrogen trioxide, however, has an unusually long N–N bond at 186 pm. Some other nitrogen oxides do also possess long N–N bonds, including dinitrogen tetroxide (175 pm). The N2O3 molecule is planar and exhibits Cs symmetry. The dimensions displayed below come from microwave spectroscopy of low-temperature, gaseous N2O3:[2]

The bond lengths and angles of dinitrogen trioxide.

The bond lengths and angles of dinitrogen trioxide.

It is the anhydride of the unstable nitrous acid (HNO2), and produces it when mixed into water. An alternative structure might be anticipated for the true anhydride, i.e. O=N–O–N=O, but this isomer is not observed. If the nitrous acid is not then used up quickly, it decomposes into nitric oxide and nitric acid. Nitrite salts are sometimes produced by adding N2O3 to solutions of bases:

N2O3 + 2 NaOH → 2 NaNO2 + H2O


  1. ^ a b c Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 444. ISBN 978-0-08-037941-8.
  2. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 521–22. ISBN 978-0-08-022057-4.
  3. ^ Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN 0-12-352651-5

External links

Arsenic acid

Arsenic acid is the chemical compound with the formula H3AsO4. More descriptively written as AsO(OH)3, this colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic acid as such has not been isolated, but is only found in solution, where it is largely ionized. Its hemihydrate form (H3AsO4·​1⁄2H2O) does form stable crystals. Crystalline samples dehydrate with condensation at 100 °C.

Cinnamyl acetate

Cinnamyl acetate (3-phenylprop-2-enyl acetate) is a chemical compound of the cinnamyl ester family, in which the variable R group is substituted by a methyl group. As a result of the non-aromatic carbon-carbon double bond, cinnamyl acetate can exist in a Z and an E configuration:

Cinnamyl acetate naturally occurs in fresh bark of cinnamon (Cinnamomum zeylanicum Blume and other Cinnamomum species), with concentrations of 2,800–51,000 ppm.Cinnamyl acetate is used as a flavour ester in for example bread and animal feed and has a sweet floral-fruity fragrance. Moreover, it is used in several cosmetics, some toiletries but also in non-cosmetic products, for example detergents.


Cinnoline is an aromatic heterocyclic compound with the formula C8H6N2. It is isomeric with other naphthyridines including quinoxaline, phthalazine and quinazoline.

Dimethyl oxalate

Dimethyl oxalate is the organic compound with the formula (CH3O2C)2. It is the dimethyl ester of oxalic acid. Dimethyl oxalate is a colorless or white solid that is soluble in water.

Dinitrogen oxide

Dinitrogen oxide can potentially refer to any of at least four compounds:

Dinitrogen monoxide (nitrous oxide), N2O;

Dinitrogen dioxide, N2O2;

Dinitrogen trioxide, N2O3;

Dinitrogen tetroxide, N2O4, an unstable dimer of nitric oxide;

Dinitrogen pentoxide, N2O5.

Dinitrogen pentoxide

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 when dissolved in chloroform 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 polar molecule:

[NO2+][NO3−] ⇌ N2O5

Dinitrogen tetroxide

Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide, is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium mixture with nitrogen dioxide.

Dinitrogen tetroxide is a powerful oxidizer that is hypergolic (spontaneously reacts) upon contact with various forms of hydrazine, which has made the pair a common bipropellant for rockets.

Kipp's apparatus

Kipp's apparatus, also called Kipp generator, is an apparatus designed for preparation of small volumes of gases. It was invented around 1844 by the Dutch pharmacist Petrus Jacobus Kipp and widely used in chemical laboratories and for demonstrations in schools into the second half of the 20th century.

It later fell out of use, at least in laboratories, because most gases then became available in small gas cylinders. These industrial gases are much purer and drier than those initially obtained from a Kipp apparatus without further processing.

List of inorganic compounds

Although most compounds are referred to by their IUPAC systematic names (following IUPAC nomenclature), "traditional" names have also been kept where they are in wide use or of significant historical interests.

Nitric oxide

Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula NO. It is one of the principal oxides of nitrogen. Nitric oxide is a free radical, i.e., it has an unpaired electron, which is sometimes denoted by a dot in its chemical formula, i.e., ·NO. Nitric oxide is also a heteronuclear diatomic molecule, a historic class that drew researches which spawned early modern theories of chemical bonding.An important intermediate in chemical industry, nitric oxide forms in combustion systems and can be generated by lightning in thunderstorms. In mammals, including humans, nitric oxide is a signaling molecule in many physiological and pathological processes. It was proclaimed the "Molecule of the Year" in 1992. The 1998 Nobel Prize in Physiology or Medicine was awarded for discovering nitric oxide's role as a cardiovascular signalling molecule.

Nitric oxide should not be confused with nitrous oxide (N2O), an anesthetic, or with nitrogen dioxide (NO2), a brown toxic gas and a major air pollutant.


The nitrite ion, which has the chemical formula NO−2, is a symmetric anion with equal N–O bond lengths. Upon protonation, the unstable weak acid nitrous acid is produced. Nitrite can be oxidized or reduced, with the product somewhat dependent on the oxidizing/reducing agent and its strength. The nitrite ion is an ambidentate ligand, and is known to bond to metal centers in at least five different ways. Nitrite is also important in biochemistry as a source of the potent vasodilator nitric oxide. In organic chemistry the NO−2 group is present in nitrous acid esters and nitro compounds. Nitrite (mostly sodium nitrite) is also used in the food production industry for curing meat.Nitrate or nitrite (ingested) under conditions that result in endogenous nitrosation has been classified as "Probably carcinogenic to humans" (Group 2A) by International Agency for Research on Cancer (IARC), the specialized cancer agency of the World Health Organization (WHO) of the United Nations.


Nitrogen is the chemical element with the symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about the same time, Rutherford is generally accorded the credit because his work was published first. The name nitrogène was suggested by French chemist Jean-Antoine-Claude Chaptal in 1790, when it was found that nitrogen was present in nitric acid and nitrates. Antoine Lavoisier suggested instead the name azote, from the Greek ἀζωτικός "no life", as it is an asphyxiant gas; this name is instead used in many languages, such as French, Russian, Romanian and Turkish, and appears in the English names of some nitrogen compounds such as hydrazine, azides and azo compounds.

Nitrogen is the lightest member of group 15 of the periodic table, often called the pnictogens. The name comes from the Greek πνίγειν "to choke", directly referencing nitrogen's asphyxiating properties. It is a common element in the universe, estimated at about seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bind to form dinitrogen, a colourless and odorless diatomic gas with the formula N2. Dinitrogen forms about 78% of Earth's atmosphere, making it the most abundant uncombined element. Nitrogen occurs in all organisms, primarily in amino acids (and thus proteins), in the nucleic acids (DNA and RNA) and in the energy transfer molecule adenosine triphosphate. The human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes movement of the element from the air, into the biosphere and organic compounds, then back into the atmosphere.

Many industrially important compounds, such as ammonia, nitric acid, organic nitrates (propellants and explosives), and cyanides, contain nitrogen. The extremely strong triple bond in elemental nitrogen (N≡N), the second strongest bond in any diatomic molecule after carbon monoxide (CO), dominates nitrogen chemistry. This causes difficulty for both organisms and industry in converting N2 into useful compounds, but at the same time means that burning, exploding, or decomposing nitrogen compounds to form nitrogen gas releases large amounts of often useful energy. Synthetically produced ammonia and nitrates are key industrial fertilisers, and fertiliser nitrates are key pollutants in the eutrophication of water systems.

Apart from its use in fertilisers and energy-stores, nitrogen is a constituent of organic compounds as diverse as Kevlar used in high-strength fabric and cyanoacrylate used in superglue. Nitrogen is a constituent of every major pharmacological drug class, including antibiotics. Many drugs are mimics or prodrugs of natural nitrogen-containing signal molecules: for example, the organic nitrates nitroglycerin and nitroprusside control blood pressure by metabolizing into nitric oxide. Many notable nitrogen-containing drugs, such as the natural caffeine and morphine or the synthetic amphetamines, act on receptors of animal neurotransmitters.

Nitrous acid

Nitrous acid (molecular formula HNO2) is a weak and monobasic acid known only in solution and in the form of nitrite (NO−2) salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes.


An oxide is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– atom. Metal oxides thus typically contain an anion of oxygen in the oxidation state of −2. Most of the Earth's crust consists of solid oxides, the result of elements being oxidized by the oxygen in air or in water. Hydrocarbon combustion affords the two principal carbon oxides: carbon monoxide and carbon dioxide. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 (called a passivation layer) that protects the foil from further corrosion. Individual elements can often form multiple oxides, each containing different amounts of the element and oxygen. In some cases these are distinguished by specifying the number of atoms as in carbon monoxide and carbon dioxide, and in other cases by specifying the element's oxidation number, as in iron(II) oxide and iron(III) oxide. Certain elements can form many different oxides, such as those of nitrogen.

Phosphorus trioxide

Phosphorus trioxide is the chemical compound with the molecular formula P4O6. Although it should properly be named tetraphosphorus hexoxide, the name phosphorus trioxide preceded the knowledge of the compound's molecular structure, and its usage continues today. This colorless solid is structurally related to adamantane. It is formally the anhydride of phosphorous acid, H3PO3, but cannot be obtained by the dehydration of the acid. It is a white, waxy, crystalline and highly toxic solid with garlic odour.

Reactive nitrogen species

Reactive nitrogen species (RNS) are a family of antimicrobial molecules derived from nitric oxide (•NO) and superoxide (O2•−) produced via the enzymatic activity of inducible nitric oxide synthase 2 (NOS2) and NADPH oxidase respectively. NOS2 is expressed primarily in macrophages after induction by cytokines and microbial products, notably interferon-gamma (IFN-γ) and lipopolysaccharide (LPS).Reactive nitrogen species act together with reactive oxygen species (ROS) to damage cells, causing nitrosative stress. Therefore, these two species are often collectively referred to as ROS/RNS.

Reactive nitrogen species are also continuously produced in plants as by-products of aerobic metabolism or in response to stress.


S-Nitrosoglutathione (GSNO) is an endogenous S-nitrosothiol (SNO) that plays a critical role in nitric oxide (NO) signaling and is a source of bioavailable NO. NO coexists in cells with SNOs that serve as endogenous NO carriers and donors. SNOs spontaneously release NO at different rates and can be powerful terminators of free radical chain propagation reactions, by reacting directly with ROO• radicals, yielding nitro derivatives as end products. NO is generated intracellularly by the nitric oxide synthase (NOS) family of enzymes: nNOS, eNOS and iNOS while the in vivo source of many of the SNOs is unknown. In oxygenated buffers, however, formation of SNOs is due to oxidation of NO to dinitrogen trioxide (N2O3). Some evidence suggests that both exogenous NO and endogenously derived NO from nitric oxide synthases can react with glutathione to form GSNO.


A trioxide is a compound with three oxygen atoms. For metals with the M2O3 formula there are several common structures. Al2O3, Cr2O3, Fe2O3, and V2O3 adopt the corundum structure. Many rare earth oxides adopt the "A-type rare earth structure" which is hexagonal. Several others plus indium oxide adopt the "C-type rare earth structure", also called "bixbyite", which is cubic and related to the fluorite structure.

Nitrogen species
Mixed oxidation states
+1 oxidation state
+2 oxidation state
+3 oxidation state
+4 oxidation state
+5 oxidation state
+6 oxidation state
+7 oxidation state
+8 oxidation state

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