Angeli's salt

Angeli's salt

File:Angeli's salt.svg
Identifiers
CAS Number	13826-64-7 checkY
3D model (JSmol)	Interactive image
ChemSpider	26377875 8549896
ECHA InfoCard
E number
PubChem CID	10129945
UNII	S8LUE47R4Z checkY
CompTox Dashboard (EPA)	{{#property:P3117}}
InChI InChI=1S/N2O3.2Na/c3-1-2(4)5;;/q;2*+1 Key: XDPWLJKQGUTUKZ-UHFFFAOYSA-N
SMILES N(=O)[N+](=O)[O-].[Na+].[Na+]
Properties
Chemical formula	N2Na2O3
Molar mass	121.991 g·mol−1
Appearance	white solid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Angeli's salt, sodium trioxodinitrate, is the inorganic compound with the formula Na₂[N₂O₃]. It contains nitrogen in an unusual reduced state. It is a colorless, water-soluble solid, hence a salt. In research, this salt is used as a source of the metastable nitroxyl (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 in 1896, the salt is prepared by combining hydroxylamine and an organic nitrate, as a source of nitronium (NO⁺
₂):

NH₂OH + RONO₂ + 2 NaOR′ → ROH + 2 R′OH + Na₂N₂O₃

The structure of the hydrate has been confirmed by X-ray crystallography. 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_trans), and 1.32 Å (N–O_cis). 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, and that the cis oxygen is slightly repelled by the single oxygen.

Reaction of Angeli's salt with secondary amines in the presence of a proton source results in extrusion of N₂ via isodiazenes as proposed intermediates.