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Sodium hyponitrite

Chemical compound From Wikipedia, the free encyclopedia

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

Quick Facts Identifiers, Properties ...

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]

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Trans isomer

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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 reduction of sodium nitrite with sodium amalgam.[5][6][7]

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[4][8]

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[citation needed].

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
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;[12][3][13] 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−).[16][1]

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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
2
O
with 77 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] It  was also obtained in 2021 by Carl Hoff and co-workers by ball milling (mechano-chemistry) sodium oxide sodium oxide Na
2
O
with 30 psi of nitrous oxide N
2
O
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
2
N
2
O
2
→ 2 (NaO)
3
N
+ 2 N
2

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

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See also

References

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