Sodium hyponitrite explained

Sodium hyponitrite is a solid ionic compound with formula or ₂[ON=NO]²⁻.^[1]

There are cis and trans forms of the hyponitrite ion . The trans form is more common, but the cis form can be obtained too, and it is more reactive than the trans form.^[1]

Trans isomer

The trans isomer is colorless and soluble in water and insoluble in ethanol and ether.^[2]

Preparation

Sodium hyponitrite (trans) is conventionally prepared by reduction of sodium nitrite with sodium amalgam.^{[3] [4]}

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 ethoxide^{[5] [6]}

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

An earlier method, published by D. Mendenhall in 1974, reacted gaseous nitric oxide with sodium metal in 1,2-dimethoxyethane, toluene, and benzophenone. The salt was then extracted with water.^[7] 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; or electrolysis of sodium nitrite.^[8]

Hydrates

A variety of hydrates _x of the trans isomer have been reported, with x including 2, 3.5, 4, 5, 6, 7, 8, and 9;^{[9] [2] [10]} but there is some dispute.^[11]

The hydration water seems to be just trapped in the crystal lattice rather than coordinated to the ions.^[11] The anhydrous substance can be obtained by drying the hydrates over phosphorus pentoxide and then heating them to 120 °C.^[11]

Reactions

Sodium hyponitrite (trans) in solution is decomposed by carbon dioxide from air to form sodium carbonate.^[12]

Liquid N₂O₄ oxidises sodium hyponitrite (trans) to give sodium peroxohyponitrite [ON=NOO]²⁻).^{[13] [1]}

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.

Preparation

The cis isomer of can be prepared by passing nitric oxide 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 with 77 kPa of nitrous oxide (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.^[14]

Properties and reactions

The anhydrous cis salt is stable up to 325 °C, when it disproportionates to nitrogen and sodium orthonitrite:^[14]

3 → 2 + 2 It is generally more reactive than the trans isomer.^[1]

See also

• Hyponitrous acid

Notes and References

1. Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier
2. Trambaklal Mohanlal Oza, Rajnikant Hariprasad Thaker (1955), "The Thermal Decomposition of Silver Hyponitrite". Journal of the American Chemical society, volume 77, issue 19, pages 4976–4980.
3. Addison, C. C. . Gamlen G. A. . Thompson, R. . . 1952 . 338–345 . 10.1039/jr9520000338 . 70. The ultra-violet absorption spectra of sodium hyponitrite and sodium α-oxyhyponitrite : the analysis of mixtures with sodium nitrite and nitrate.
4. Neumann, R. C., Jr. Bussey, R. J. . . 1970 . 92 . 2440–2445 . 10.1021/ja00711a039 . High pressure studies. V. Activation volumes for combination and diffusion of geminate tert-butoxy radicals . 8.
5. A. W. Scott (1927), "Sodium Hyponitrite". J. Am. Chem. Soc., volume = 49, issue 4, pages = 986–987.
6. Book: Inorganic Chemistry . 3rd . Chapter 15: The group 15 elements . Catherine E. Housecroft . Alan G. Sharpe. Pearson . 2008 . 978-0-13-175553-6 . 468.
7. G. David Mendenhall (1974), "Convenient synthesis of silver hyponitrite". Journal of the American Chemical society, volume 96, issue 15, page 5000.
8. Polydoropoulos, C. N. Chem. Ind. (London) 1963, 1686 and references therein.
9. James Riddick Partington and Chandulal Chhotalal Shah (1931), "Investigations on hyponitrites. Part I. Sodium hyponitrite: preparation and properties". Journal of the Chemical Society (Resumed), paper CCLXXXII, pages 2071-2080.
10. C.N. Polydoropoulos, S.D. Voliotis (1967), "Sodium hyponitrite hexahydrate". Journal of Inorganic and Nuclear Chemistry, volume 29, issue 12, pages 2899–2901.
11. Gary L. Stucky, Jack L. Lambert, R. Dean Dragsdorf (1969), "The hydrates of sodium hyponitrite". Journal of Inorganic and Nuclear Chemistry, volume 31, issue 1, pages 29–32
12. Charlotte N. Conner, Caroline E. Donald, Martin N. Hughes, Christina Sami (1989), "The molar absorptivity of sodium hyponitrite". Polyhedron, volume 8, issue 21, pages 2621-2622.
13. M. N. Hughes and H. G. Nicklin (1969), "The action of dinitrogen tetroxide on sodium hyponitrite". Journal of the Chemical Society D: Chemical Communications, volume 1969, issue 2, page 80a.
14. Claus Feldmann, Martin Jansen (1996), "cis-Sodium Hyponitrite - A New Preparative Route and a Crystal Structure Analysis". Angewandte Chemie International Edition in English, volume 35, issue 15, pages 1728–1730.