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Sodium hyponitrite

Sodium hyponitrite is a solid ionic compound with formula Na2N2O2 or (Na+)2[ON=NO]2−.

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Jul 19, 2026
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Sodium hyponitrite (trans isomer)
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Identifiers
3D model (JSmol)
ChemSpider
  • InChI=1S/H2N2O2.2Na/c3-1-2-4;;/h(H,1,4)(H,2,3);;/q;2*+1/p-2
    Key: HLJWMCUZPYEUDI-UHFFFAOYSA-L
  • N(=N[O-])[O-].[Na+].[Na+]
  • trans-form: [Na+].[O-]/N=N/[O-].[Na+]
  • cis-form: [Na+].[O-]\N=N/[O-].[Na+]
Properties
Na2N2O2
Molar mass 105.99 g/mol
Appearance colorless crystals
Density 2.466 g/cm3
Melting point 100 °C (212 °F; 373 K)
Boiling point 335 °C (635 °F; 608 K) decomposes
soluble
Solubility insoluble in ethanol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Sodium hyponitrite is a solid ionic compound with formula Na
2N
2O
2 or (Na+
)2[ON=NO]2−.1

There are cis and trans forms of the hyponitrite ion N
2O2−
2. The trans form is more common, but the cis form can be obtained too, and it is more reactive than the trans form.12

Trans isomer

The trans isomer is colorless and soluble in water and insoluble in ethanol and ether.34

Preparation

Sodium hyponitrite (trans) is conventionally prepared by reduction of sodium nitrite with sodium amalgam.567

2 NaNO2 + 4 Na(Hg) + 2 H2O → Na2N2O2 + 4 NaOH + 4 Hg

Sodium hyponitrite (trans) was prepared in 1927 by A. W. Scott by reacting alkyl nitrites, hydroxylammonium chloride, and sodium ethoxide48

RONO + NH2OH + 2 EtONa → Na2N2O2 + ROH + 2 EtOH

An earlier method, published by D. Mendenhall in 1974, reacted gaseous nitric oxide (NO) with sodium metal in 1,2-dimethoxyethane, toluene, and benzophenone. The salt was then extracted with water.9 The method was later modified to use pyridine.

Other methods included oxidation of a concentrated solution of hydroxylamine with sodium nitrite in an alkaline medium:
NH2OH (conc.) + NaNO2 + NaOH → Na2N2O2 + 2H2O;10
or electrolysis of sodium nitrite.11

Hydrates

A variety of hydrates Na
2N
2O
2(H
2O)x of the trans isomer have been reported, with x including 2, 3.5, 4, 5, 6, 7, 8, and 9;12313 but there is some dispute.14

The hydration water seems to be just trapped in the crystal lattice rather than coordinated to the ions.14 The anhydrous substance can be obtained by drying the hydrates over phosphorus pentoxide and then heating them to 120 °C.14

Reactions

Sodium hyponitrite (trans) in solution is decomposed by carbon dioxide CO
2 from air to form sodium carbonate.15

Liquid N2O4 oxidises sodium hyponitrite (trans) to give sodium peroxohyponitrite Na2+
2[ON=NOO]2−).161

Cis isomer

The cis isomer of sodium hyponitrite is a white crystalline solid, insoluble in aprotic solvents, and (unlike the trans isomer) decomposed by water and other protic solvents.2

Preparation

The cis isomer of sodium hyponitrite can be prepared by passing nitric oxide (NO) through a solution of sodium metal in liquid ammonia at −50 °C.1

The cis isomer was also obtained in 1996 by C. Feldmann and M. Jansen by heating sodium oxide Na
2O with 77 kPa of nitrous oxide N
2O (laughing gas) in a sealed tube at 360 °C for 2 hours. The two reagents combined to yield the cis hyponitrite quantitatively as white microcrystals.82 It  was also obtained in 2021 by Carl Hoff and co-workers by ball milling (mechano-chemistry) sodium oxide sodium oxide Na
2O with 30 psi of nitrous oxide N
2O for 4 hours at room temperature.17

Properties and reactions

The anhydrous cis salt is stable up to 325 °C, when it disproportionates to nitrogen and sodium orthonitrite:2

3 Na
2N
2O
2 → 2 (NaO)
3N + 2 N
2

It is generally more reactive than the trans isomer.1

See also

See also

References

References

  1. Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5
  2. Feldmann, Claus; Jansen, Martin (1996). "cis -Sodium Hyponitrite—A New Preparative Route and a Crystal Structure Analysis". Angewandte Chemie International Edition in English. 35 (15): 1728–1730. doi:10.1002/anie.199617281.
  3. Oza, Trambaklal Mohanlal; Thaker, Rajnikant Hariprasad (1955). "The Thermal Decomposition of Silver Hyponitrite". Journal of the American Chemical Society. 77 (19): 4976–4980. Bibcode:1955JAChS..77.4976O. doi:10.1021/ja01624a007.
  4. Scott, Alfred W. (1927). "Sodium Hyponitrite". Journal of the American Chemical Society. 49 (4): 986–987. Bibcode:1927JAChS..49..986S. doi:10.1021/ja01403a502.
  5. Addison, C. C.; Gamlen, G. A.; Thompson, R. (1952). "70. The ultra-violet absorption spectra of sodium hyponitrite and sodium α-oxyhyponitrite : the analysis of mixtures with sodium nitrite and nitrate". Journal of the Chemical Society: 338–345. doi:10.1039/jr9520000338.
  6. Neuman, Robert C.; Bussey, Robert J. (1970). "High pressure studies. V. Activation volumes for combination and diffusion of geminate tert-butoxy radicals". Journal of the American Chemical Society. 92 (8): 2440–2445. Bibcode:1970JAChS..92.2440N. doi:10.1021/ja00711a039.
  7. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
  8. Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 15: The group 15 elements". Inorganic Chemistry (3rd ed.). Pearson. p. 468. ISBN 978-0-13-175553-6.
  9. Mendenhall, G. David (1974). "Convenient synthesis of silver hyponitrite". Journal of the American Chemical Society. 96 (15): 5000. Bibcode:1974JAChS..96.5000M. doi:10.1021/ja00822a054.
  10. Р.А. Лидин, В.А. Молочко, Л.Л. Андреева, Химические свойства неорганических веществ: учебное пособие.
  11. Polydoropoulos, C. N. Chem. Ind. (London) 1963, 1686 and references therein.
  12. Partington, James Riddick; Shah, Chandulal Chhotalal (1931). "CCLXXXII.—Investigations on hyponitrites. Part I. Sodium hyponitrite: Preparation and properties". Journal of the Chemical Society: 2071–2080. doi:10.1039/JR9310002071.
  13. Polydoropoulos, C.N.; Voliotis, S.D. (1967). "Sodium hyponitrite hexahydrate". Journal of Inorganic and Nuclear Chemistry. 29 (12): 2899–2901. doi:10.1016/0022-1902(67)80121-0.
  14. Stucky, Gary L.; Lambert, Jack L.; Dean Dragsdorf, R. (1969). "The hydrates of sodium hyponitrite". Journal of Inorganic and Nuclear Chemistry. 31: 29–32. doi:10.1016/0022-1902(69)80050-3.
  15. Conner, Charlotte N.; Donald, Caroline E.; Hughes, Martin N.; Sami, Christina (1989). "The molar absorptivity of sodium hyponitrite". Polyhedron. 8 (21): 2621–2622. doi:10.1016/S0277-5387(00)81166-3.
  16. Hughes, M. N.; Nicklin, H. G. (1969). "The action of dinitrogen tetroxide on sodium hyponitrite". Journal of the Chemical Society D: Chemical Communications (2): 80a. doi:10.1039/C2969000080A.
  17. Davis, Jack V.; Guio, Oswaldo; Captain, Burjor; Hoff, Carl D. (2021). "Production of cis -Na2N2O2 and NaNO3 by Ball Milling Na2O and N2O in Alkali Metal Halide Salts". ACS Omega. 6 (28): 18248–18252. doi:10.1021/acsomega.1c02119. PMC 8296613. PMID 34308055.