Angeli's salt, sodium trioxodinitrate, is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

with the formula Na₂ ₂O₃ It contains nitrogen in an unusual reduced state. It is a colorless, water-soluble solid, a salt. In research, this salt is used as a source of the metastable

nitroxyl Nitroxyl (common name) or azanone (IUPAC name) is the chemical compound HNO. It is well known in the gas phase. Nitroxyl can be formed as a short-lived intermediate in the solution phase. The conjugate base, NO−, nitroxide anion, is the redox re ...

(HNO), which is a signalling molecule in nature. It is also known by the name sodium trioxodinitrate(II) monohydrate.

Preparation and properties

As first reported by

Angelo Angeli Angelo Angeli (20 August 1864 – 31 May 1931) was an Italian chemist. Angeli's salt and the Angeli–Rimini reaction are named after him. Scientific career Angeli studied in Padua, where he met the chemist Giacomo Luigi Ciamician. When C ...

in 1896, the salt is prepared by combining hydroxylamine and an organic nitrate, as a source of

nitronium The nitronium ion, , is a cation. It is an onium ion because its nitrogen atom has +1 charge, similar to ammonium ion . It is created by the removal of an electron from the paramagnetic nitrogen dioxide molecule , or the protonation of nitric aci ...

(): :NH₂OH + RONO₂ + 2 NaOR′ → ROH + 2 R′OH + Na₂N₂O₃ The structure of the hydrate has been confirmed by

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

. The anion is planar. Starting from the ONN end, the bond distances are 1.35 Å (N−O), 1.26 Å (N−N), 1.31 Å (N−O), and 1.32 Å (N−-O). The negative charge is on the oxygen atoms at opposite ends of the molecule. The angles are 112.9° (O_single−N−N), 118.4° (N−N−O_''trans''), and 122.5° (N−N−O_''cis''). This means that the nitrogen–nitrogen bond is a

double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...

, and that the ''cis'' oxygen is slightly repelled by the single oxygen. Reaction of Angeli's salt with

secondary amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such a ...

s in the presence of a proton source results in extrusion of N₂ via

isodiazene In organic chemistry, an isodiazene, also known by the incorrectly constructed (but commonly used) name 1,1-diazene or systematic name diazanylidene, is an organic derivative of the parent isodiazene (H2N+=N–, also called 1,1-diimide) with genera ...

s as proposed intermediates.

References

{{reflist Nitrites Sodium compounds