Angeli's salt

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Angeli's salt
Angeli's salt.svg
3D model (JSmol)
  • InChI=1S/N2O3.2Na/c3-1-2(4)5;;/q;2*+1
  • N(=O)[N+](=O)[O-].[Na+].[Na+]
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).

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.

Preparation and properties[edit]

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+

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° (Osingle−N−N), 118.4° (N−N−Otrans), and 122.5° (N−N−Ocis). 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]


  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". Methods in Enzymology (Nitric Oxide, Part C: Biological and Antioxidant Activities). 301: 279–287. doi:10.1016/S0076-6879(99)01092-7. 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.