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Sodium hyponitrite
Chemical compound From Wikipedia, the free encyclopedia
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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.[1][2]
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Trans isomer
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Perspective
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
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;[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
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.[8][2] 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]
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See also
References
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