Hyponitrite
Encyclopedia
A hyponitrite refers to ionic compounds that contain the hyponitrite ion, N2O22−, ([ON=NO]2−) or to organic hyponitrites (RON=NOR), for example di-tert butyl hyponitrite.
The trans-isomer is conventionally prepared by nitrite
reduction with sodium amalgam.
Sodium hyponitrite can be prepared from sodium and nitric oxide by a method described by an earlier method modified with pyridine, from sodium amalgam and sodium nitrite, from alkyl nitrites and hydroxylamine or by electrolysis of sodium nitrite.
The cis-isomer of the sodium salt, NaN2O2, can be prepared by passing nitrous oxide
, NO into a solution of sodium
metal in liquid ammonia
at -50 °C.The cis salt is more reactive than the trans. The trans - hyponitrite ion is a salt of the related trans-hyponitrous acid
H2N2O2 ( HON=NOH ), the cis acid is not known.
The hyponitrite ions can act as a bidentate ligand in either bridging or chelating mode. There is a bridging cis-hyponitrite group in the red dinuclear form of nitrosyl pentammine cobalt(III) chloride, [Co(NH3)5NO]Cl2.
Hyponitrite can act as a reducing agent for example reducing iodine, I2,:
Liquid N2O4
oxidises hyponitrites to give Na2N2O3, sodium peroxohyponitrite (containing [ON=NOO]2−).
and water with a half life of 16 days at 25°C at pH 1-3. As this reaction is not reversible N2O should not be considered as the anhydride of H2N2O2. Hyponitrous acid forms salts, the "acid hyponitrites" containing the [HON=NO]− anion as well as the hyponitrites that contain the [ON=NO]2− anion.
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Hyponitrite ion
There are cis and trans forms of the hyponitrite ion. The trans form is generally found in hyponitrite salts such as sodium hyponitrite, Na2N2O2 and silver hyponitrite, Ag2N2O2.The trans-isomer is conventionally prepared by nitrite
Nitrite
The nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...
reduction with sodium amalgam.
Sodium hyponitrite can be prepared from sodium and nitric oxide by a method described by an earlier method modified with pyridine, from sodium amalgam and sodium nitrite, from alkyl nitrites and hydroxylamine or by electrolysis of sodium nitrite.
The cis-isomer of the sodium salt, NaN2O2, can be prepared by passing nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
, NO into a solution of sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
metal in liquid ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
at -50 °C.The cis salt is more reactive than the trans. The trans - hyponitrite ion is a salt of the related trans-hyponitrous acid
Hyponitrous acid
Hyponitrous acid is the chemical compound H2N2O2. This can be formulated as HON=NOH and is an isomer of nitramide, . It forms white crystals that are explosive when dry...
H2N2O2 ( HON=NOH ), the cis acid is not known.
The hyponitrite ions can act as a bidentate ligand in either bridging or chelating mode. There is a bridging cis-hyponitrite group in the red dinuclear form of nitrosyl pentammine cobalt(III) chloride, [Co(NH3)5NO]Cl2.
Hyponitrite can act as a reducing agent for example reducing iodine, I2,:
- N2O22− + 3I2 + 3H2O = [NO3]− + [NO2]− + 6HI
Liquid N2O4
Dinitrogen tetroxide
Dinitrogen tetroxide is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium mixture with nitrogen dioxide; some call this mixture dinitrogen tetroxide, while some call it nitrogen dioxide.Dinitrogen tetroxide is a powerful oxidizer, making it highly...
oxidises hyponitrites to give Na2N2O3, sodium peroxohyponitrite (containing [ON=NOO]2−).
Hyponitrous acid
Trans-hyponitrous acid forms white crystals that are explosive when dry. It is a weak acid in aqueous solution and decomposes to N2ONitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
and water with a half life of 16 days at 25°C at pH 1-3. As this reaction is not reversible N2O should not be considered as the anhydride of H2N2O2. Hyponitrous acid forms salts, the "acid hyponitrites" containing the [HON=NO]− anion as well as the hyponitrites that contain the [ON=NO]2− anion.
Other nitrogen oxoanions
Other nitrogen oxoanions include- nitrateNitrateThe nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
, NO3− - nitriteNitriteThe nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...
, NO2− - peroxonitritePeroxynitritePeroxynitrite is the anion with the formula ONOO−. It is an unstable structural isomer of nitrate, NO3−, which has the same formula but a different structure. Although peroxynitrous acid is highly reactive, its conjugate base peroxynitrite is stable in basic solution...
, (peroxynitrite), OONO− - peroxonitratePeroxynitratePeroxynitrate refers to salts of the unstable peroxynitric acid, HNO4, however no solid salts are known....
, HNO4− - trioxodinitrate, (hyponitrate), [ON=NO2]2−
- nitroxylate, [O2N−NO2]4−
- orthonitrateOrthonitrateThe orthonitrate ion is NO43−. It is only known in two compounds, Na3NO4 and K3NO4 which were prepared by fusion of the nitrate and oxide, e.g....
[NO4]3−
Alkyl hyponitrites
Silver hyponitrite reacts with alkyl halides, RX, to form organic hyponitrites, (RON=NOR) , e.g. trans t-butyl hyponitrites. One use of these is as a source of alkoxyl radicalsRadical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...
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