Sodium hyponitrite

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Sodium hyponitrite (trans isomer)
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
2
N
2
O
2
or (Na+
)2[ON=NO]2−.[1]

There are cis and trans forms of the hyponitrite ion N
2
O2−
2
. The trans form is more common, but the cis form can be obtained too, and it is more reactive than the trans form.[1][2]

Trans isomer

The trans isomer is colorless and soluble in water and insoluble in ethanol and ether.[3][4]

Preparation

Sodium hyponitrite (trans) is conventionally prepared by

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

Sodium hyponitrite (trans) was prepared in 1927 by

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

An earlier method, published by

1,2-dimethoxyethane, toluene, and benzophenone. The salt was then extracted with water.[9] The method was later modified to use pyridine[citation needed
].

Other methods included

oxidation of a concentrated solution of hydroxylamine with sodium nitrite in an alkaline medium[citation needed]; or electrolysis of sodium nitrite.[10]

Hydrates

A variety of

hydrates Na
2
N
2
O
2
(H
2
O
)x of the trans isomer have been reported, with x including 2, 3.5, 4, 5, 6, 7, 8, and 9;[11][3][12] but there is some dispute.[13]

The hydration water seems to be just trapped in the crystal lattice rather than coordinated to the ions.[13] The anhydrous substance can be obtained by drying the hydrates over phosphorus pentoxide and then heating them to 120 °C.[13]

Reactions

Sodium hyponitrite (trans) in solution is decomposed by carbon dioxide CO
2
from air to form sodium carbonate.[14]

Liquid N2O4 oxidises sodium hyponitrite (trans) to give sodium peroxohyponitrite Na2+
2
[ON=NOO]2−).[15][1]

Cis isomer

The cis isomer of sodium hyponitrite is a white crystalline solid, insoluble in

protic solvents.[2]

Preparation

The cis isomer of 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

kPa of nitrous oxide N
2
O
(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.[8][2]

Properties and reactions

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

3 Na
2
N
2
O
2
→ 2 Na
3
O
(NO
2
) + 2 N
2

It is generally more reactive than the trans isomer.[1]

See also

References

  1. ^
  2. ^
  3. ^
  4. ^
  5. .
  6. doi:10.1021/ja00711a039.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  7. .
  8. ^ .
  9. ^ Polydoropoulos, C. N. Chem. Ind. (London) 1963, 1686 and references therein.
  10. ^
  11. ^ 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.