Sodium hyponitrite is a solid
ionic compound
In chemistry, an ionic compound is a chemical compound composed of ions held together by electrostatic forces termed ionic bonding. The compound is neutral overall, but consists of positively charged ions called cations and negatively charged i ...
with formula or ()
2 N=NOsup>2−.
[Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier ]
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.
''Trans'' isomer
The ''trans'' isomer is colorless and soluble in water and insoluble in
ethanol and
ether.
[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. ]
Preparation
Sodium hyponitrite (''trans'') is conventionally prepared by
reduction of
sodium nitrite with
sodium amalgam.
:2 NaNO
2 + 4 Na(Hg) + 2 H
2O → Na
2N
2O
2 + 4 NaOH + 4 Hg
Sodium hyponitrite (''trans'') was prepared in 1927 by
A. W. Scott by reacting
alkyl nitrites,
hydroxylammonium chloride, and
sodium ethoxide[A. W. Scott (1927), "Sodium Hyponitrite". ]J. Am. Chem. Soc.
The ''Journal of the American Chemical Society'' is a weekly peer-reviewed scientific journal that was established in 1879 by the American Chemical Society. The journal has absorbed two other publications in its history, the ''Journal of Analytic ...
, volume = 49, issue 4, pages = 986–987.
: RONO + NH
2OH + 2 EtONa → Na
2N
2O
2 + ROH + 2 EtOH
An earlier method, published by
D. Mendenhall in 1974, reacted gaseous
nitric oxide
Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...
() with
sodium metal in
1,2-dimethoxyethane
Dimethoxyethane, also known as glyme, monoglyme, dimethyl glycol, ethylene glycol dimethyl ether, dimethyl cellosolve, and DME, is a colorless, aprotic, and liquid ether that is used as a solvent, especially in batteries. Dimethoxyethane is misc ...
,
toluene, and
benzophenone. The salt was then extracted with water.
[G. David Mendenhall (1974), "Convenient synthesis of silver hyponitrite". Journal of the American Chemical society, volume 96, issue 15, page 5000. ] 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
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
of sodium nitrite.
[Polydoropoulos, C. N. Chem. Ind. (London) 1963, 1686 and references therein.]
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;
[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. ][C.N. Polydoropoulos, S.D. Voliotis (1967), "Sodium hyponitrite hexahydrate". Journal of Inorganic and Nuclear Chemistry, volume 29, issue 12, pages 2899–2901. ] but there is some dispute.
[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 ]
The hydration water seems to be just trapped in the crystal lattice rather than coordinated to the ions.
The anhydrous substance can be obtained by drying the hydrates over
phosphorus pentoxide and then heating them to 120 °C.
Reactions
Sodium hyponitrite (''trans'') in solution is decomposed by
carbon dioxide from air to form
sodium carbonate
Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...
.
[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. ]
Liquid
N2O4 oxidises sodium hyponitrite (''trans'') to give sodium
peroxohyponitrite N=NOOsup>2−).
[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. ]
''Cis'' isomer
The ''cis'' isomer of sodium hyponitrite is a white crystalline solid, insoluble in
aprotic A polar aprotic solvent is a solvent that lacks an acidic proton and is polar. Such solvents lack hydroxyl and amine groups. In contrast to protic solvents, these solvents do not serve as proton donors in hydrogen bonding
In chemistry, a hydro ...
solvents, and (unlike the ''trans'' isomer) decomposed by water and other
protic
In chemistry, a protic solvent is a solvent that has a hydrogen atom bound to an oxygen (as in a hydroxyl group ), a nitrogen (as in an amine group or ), or fluoride (as in hydrogen fluoride). In general terms, any solvent that contains a labile ...
solvents.
Preparation
The ''cis'' isomer of can be prepared by passing
nitric oxide
Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...
() through a solution of
sodium metal in liquid
ammonia at −50 °C.
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.
[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. ]
Properties and reactions
The anhydrous ''cis'' salt is stable up to 325 °C, when it disproportionates to
nitrogen and
sodium orthonitrite:
: 3 → 2 () + 2
It is generally more reactive than the ''trans'' isomer.
See also
*
Hyponitrous acid
References
{{Sodium compounds
Sodium compounds