Angeli's salt

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.^[1] It is also known by the name sodium trioxodinitrate(II) monohydrate.

Angeli's salt

Identifiers
CAS Number	13826-64-7 Y
3D model (JSmol)	Interactive image
ChemSpider	26377875 8549896
PubChem CID	10129945
UNII	S8LUE47R4Z Y
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

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):^[2][3]

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), 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, and that the cis oxygen is slightly repelled by the single oxygen.^[4]

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.^[5]

References

1. Nakagawa, H. (2013). "Controlled release of HNO from chemical donors for biological applications". J. Inorg. Biochem. 118: 187–190. doi:10.1016/j.jinorgbio.2012.10.004. PMID 23140899.
2. Angeli, A. (1896). "Sopra la nitroidrossilammina" [On nitrohydroxylamine]. Gazz. Chim. Ital. (in Italian). 26: 17–28.
3. Hughes, Martin N.; Cammack, Richard (1999). "Synthesis, chemistry, and Applications of Nitroxyl Ion Releasers Sodium Trioxodinitrate or Angeli's Salt and Piloty's Acid". Nitric Oxide, Part C: Biological and Antioxidant Activities. Methods in Enzymology. Vol. 301. pp. 279–287. doi:10.1016/S0076-6879(99)01092-7. ISBN 9780121822026. PMID 9919577.
4. Hope, Hakon; Sequeira, Michael R. (February 1973). "Angeli's salt. Crystal structure of sodium trioxodinitrate(II) monohydrate, Na₂N₂O₃·H₂O". Inorganic Chemistry. 12 (2): 286–288. doi:10.1021/ic50120a008.
5. Carey, Francis A.; Sundberg, Richard J. (2007). Advanced Organic Chemistry. Part B: Reactions and Synthesis (5th ed.). New York, NY: Springer. ISBN 9781601195494. OCLC 223941000.