Hyponitrite Explained

In chemistry, hyponitrite may refer to the anion ([ON=NO]²⁻), or to any ionic compound that contains it. In organic chemistry, it may also refer to the group −O−N=N−O−, or any organic compound with the generic formula R¹−O−N=N−O−R², where R¹ and R² are organic groups.^[1] Such compounds can be viewed as salts and esters of hyponitrous acid.An acid hyponitrite is an ionic compound with the anion ([HON=NO]⁻).

Hyponitrite ion

Hyponitrite exhibits cis–trans isomerism.^[2]

The trans (E) form is generally found in hyponitrite salts such as sodium hyponitrite and silver(I) hyponitrite .

The cis (Z) form of sodium hyponitrite can be obtained too, but it is more reactive than the trans form.^[2] The cis hyponitrite anion is nearly planar and almost symmetric, with lengths of about 140 pm for N−O bond and 120 pm for the N−N bond, and O−N−N angles of about 119°.^[3]

Reactions

The hyponitrite ions can act as a bidentate ligand in either bridging or chelating mode. There is a bridging cis-hyponitrite group in the red dinuclear form of nitrosyl pentammine cobalt(III) chloride, [Co(NH₃)₅NO]Cl₂.

Hyponitrite can reduce elemental iodine to hydroiodic acid:

+ 3 + 3 → + + 6 HI

Hyponitrite esters

Organic trans-hyponitrites R¹−O−N=N−O−R² can be obtained by reacting trans silver(I) hyponitrite with various alkyl halides. For example, reaction with tert-butyl chloride yields trans di-tert-butyl hyponitrite.^{[4] [5] [6] [7]}

Other alkyl radicals reported in the literature include ethyl,^[8] and benzyl.^{[9] [10] [11]} These compounds can be a source of alkoxyl radicals.^[12]

See also

Other nitrogen oxyanions include

• nitrate,
• nitrite,
• peroxonitrite, (peroxynitrite), OONO⁻
• peroxonitrate,
• trioxodinitrate, (hyponitrate), [ON=NO₂]²⁻
• nitroxylate, [O₂N−NO₂]⁴⁻
• orthonitrate,

Notes and References

1. 10.1039/QR9682200001 . Hyponitrites . 1968 . Hughes . M. N. . Quarterly Reviews, Chemical Society . 22 . 1 .
2. Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier
3. 10.1002/anie.199617281 . Cis-Sodium Hyponitrite—A New Preparative Route and a Crystal Structure Analysis . 1996 . Feldmann . Claus . Jansen . Martin . Angewandte Chemie International Edition in English . 35 . 15 . 1728–1730 .
4. Correlation of the Product E/Z Framework Geometry and O/O vs O/N Regioselectivity in the Dialkylation of Hyponitrite . Navamoney Arulsamy . D. Scott Bohle . Jerome A. Imonigie . Elizabeth S. Sagan . . 2000 . 122 . 23 . 5539–5549 . 10.1021/ja994261o.
5. Kiefer . Hansruedi . Traylor . T.G. . Di-t-butyl hyponitrite. A convenient source of t-butoxy radicals . Tetrahedron Letters . 7 . 49 . 1966 . 0040-4039 . 10.1016/s0040-4039(00)70159-6 . 6163–6168.
6. Huang . R. L. . Lee . Tong-Wai . Ong . S. H. . Reactions of the α-methoxybenzyl radical in carbon tetrachloride and in other solvents. Carbon tetrachloride as a chlorinating agent . J. Chem. Soc. C . 1 . 1969 . 0022-4952 . 10.1039/j39690000040 . 40–44.
7. Neuman . Robert C. . Bussey . Robert J. . High pressure studies. V. Activation volumes for combination and diffusion of geminate tert-butoxy radicals . Journal of the American Chemical Society . 92 . 8 . 1970 . 0002-7863 . 10.1021/ja00711a039 . 2440–2445.
8. Partington . James R. . Shah . Chandulal C. . 384. Hyponitrites. Part II : metallic salts. Part III : esters . Journal of the Chemical Society . 1932 . 0368-1769 . 10.1039/jr9320002589 . 2589.
9. Ho . S. K. . de Sousa . J. B. . 347. Alkoxy-radicals. Part I. The kinetics of thermal decomposition of dibenzyl hyponitrite in solution . Journal of the Chemical Society . 1961 . 0368-1769 . 10.1039/jr9610001788 . 1788.
10. de SOUSA . J. B. . HO . S. K. . Disproportionation and Dimerization of the Benzyloxyl Free Radical in Solution . Nature . 186 . 4727 . 1960 . 0028-0836 . 10.1038/186776a0 . 776–778. 1960Natur.186..776D . 4248607 .
11. Ray . N. H. . 794. The rates of decomposition of free-radical polymerisation-catalysts: measurements of short half-lives by a thermal method . Journal of the Chemical Society . 1960 . 0368-1769 . 10.1039/jr9600004023 . 4023.
12. Decomposition rates, synthesis, and spectral properties of a series of alkyl hyponitrites . Craig A. Ogle . Steven W. Martin . Michael P. Dziobak . Marek W. Urban . G. David Mendenhall . . 1983 . 48 . 21 . 3728–3733 . 10.1021/jo00169a023.