Hypo-nitrous acid

Structural formula
Isomeric forms of hypositrous acid
General
Surname	Hypo-nitrous acid
other names	Undernitrous acid Diazenediol Hyposalpetretic acid
Molecular formula	H 2 N 2 O 2
Brief description	colorless platelets that are explosive when dry
External identifiers / databases
CAS number 14448-38-5 PubChem 61744 Wikidata Q7774
properties
Molar mass	62.0 g mol −1
Physical state	firmly
pK s value	7.21 11.54
solubility	good in water and ethanol
safety instructions
GHS hazard labeling no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Hypo-nitrous acid is an oxygen acid of nitrogen . It forms colorless crystals that are explosive. These are soluble in ethanol and water.

Their salts are called hyponitrites , e.g. E.g .: potassium hyponitrite (K ₂ N ₂ O ₂ ).

Manufacturing

trans -Hypositrous acid can be produced by reducing nitrous acid or sodium nitrite with nascent hydrogen (e.g. from sodium amalgam ).

${\displaystyle \mathrm {2\,NaNO_{2}+4\,Na_{Amalgam}+2\,H_{2}O\longrightarrow Na_{2}N_{2}O_{2}+4\,NaOH} }$

The water-soluble sodium salt can be separated as yellow, insoluble silver hyponitrite with silver nitrate :

${\displaystyle \mathrm {Na_{2}N_{2}O_{2}+2\,AgNO_{3}\longrightarrow Ag_{2}N_{2}O_{2}\downarrow +\ 2\,NaNO_{3}} }$

After separation, the trans -Hypositrous acid can be redissolved in ether with HCl gas:

${\displaystyle \mathrm {Ag_{2}N_{2}O_{2}+2\,HCl_{(g)}\longrightarrow H_{2}N_{2}O_{2}+2\,AgCl\downarrow } }$

properties

trans -Hypositrous acid is a colorless solid that is in the form of deliquescent crystal flakes and is a very weak acid. It is very explosive, fizzles out when rubbed with a glass rod and spontaneously decomposes even for no apparent reason and even when cooled to −6 ° C. It is very easily soluble in water and in ethanol , easily also in ether , benzene and trichloromethane , but difficult in ligroin .

Isomerism

There is a cis - and a more stable trans -Hyposalpetrige acid.

cis form of hypo-nitrous acid

Only the salts of the cis form are known; the trans form can be isolated in substance.

Reactions

With alkali metals constituting hyponitrous acid salts , the hyponitrites :

${\displaystyle \mathrm {H_{2}N_{2}O_{2}+2\,Na\longrightarrow Na_{2}N_{2}O_{2}+H_{2}\uparrow } }$

The weakly acidic aqueous solution of the acid breaks down to nitrous oxide and water at room temperature :

${\displaystyle \mathrm {H_{2}N_{2}O_{2}\longrightarrow H_{2}O+N_{2}O} }$

The reaction is irreversible; Dinitrogen monoxide is therefore only formally anhydride of hypo- nitrous acid.

It is also suitable as a reaction partner for hetero Diels-Alder reactions .

Individual evidence

1. ↑ ^{a b} Entry on hyposalpetretic acid. In: Römpp Online . Georg Thieme Verlag, accessed on November 10, 2014.
2. ↑ ^{a b c d e} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 .
3. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
4. ↑ ^{a b} G. Brauer (Ed.), Handbook of Preparative Inorganic Chemistry 2nd ed., Vol. 1, Academic Press 1963, pp. 492-6.
5. ↑ E. Riedel, C. Janiak: Inorganic Chemistry . 8th edition. de Gruyter, 2011, ISBN 3-11-022566-2 , p. 488 .