Hyponitrous Acid Formula: Definition, Concepts and Examples

Hyponitrous Acid

Hyponitrous Acid Formula- It is a chemical compound and isomers of nitramide (\( H_{2} N-NO_{2}\)). In this chemical compound, the property value of a hydrogen bond donor is 2 and the property value of hydrogen bond receiver or acceptor is 4. Moreover, we know it by another name that is a hyponitrous acid dimer. Also, its IUPAC (International Union of Pure and Applied Chemistry) name is E- dihydroxydiazene. Besides, the hyponitrous acid forms two series of salts, the hyponitrites that contain the \( [ON=ON]^{2-} \) anion, and the “acid hyponitrites” that contains the \( [HON= NO]^{-} \) anion.

Hyponitrous Acid Formula and Structure

Hyponitrous Acid Formula

The chemical formula of hyponitrous acid is \( H_{2} N_{2} O_{2} \) or HON=NOH. Its molecular weight is 62.028 g/mol. Furthermore, it has two possible structure that is trans and cis. The trans-hyponitrous acid forms white crystals that are explosive when they are dry.

In addition, in aqueous solution, it is a weak acid (\(pK_{a1} = 7.21, pK_{a2} = 11.54 \)), and it decomposes to nitrous oxide and water with a half-life of 16 days at \( 25^{o}C \) at a pH 1-3:

\( H_{2} N_{2} O_{2} \rightarrow H_{2}O + N_{2} O\)

As this reaction is non-reversible, \( N_{2} O\) should not be considered as the anhydride of \( H_{2} N_{2} O_{2} \). On the other hand, cis acid is unknown; still, we can obtain its sodium salts.

This compound contains the diazo-group, which indicates in many reactions that we observe in many of the reactions we use it in its preparation.

Preparation of Hyponitrous Acid

We can prepare it by various methods such as:

We can prepare hyponitrous acid (trans) from silver (i) hyponitrite and anhydrous HCl in the ether:

\( Ag_{2} N_{2} O_{2} + 2 HCl \rightarrow H_{2} N_{2} O_{2} + 2 AgCl\)

Most noteworthy, the spectroscopic data indicate a trans configuration for the resulting acid.

Furthermore, we can also prepare hyponitrous acid by reducing ferrous hydroxide. We precipitate pure ferrous sulfate with milk of lime, and then we cool it. Moreover, in this mixture, we add 1 mol. Of \( NaNO_{3} \) for each 10 mols. Of \( FeSO_{4} \). After this, we precipitate this hyponitrite with silver nitrate.

We add a solution of \( NaNO_{2} \) to the solution of \( NH_{2} OH \cdot H_{2} SO_{4} \). Moreover, we quickly heat this mixture to \( 60^{o}C \), and \( AgNO_{3} \) is added at once. However, this method does not give good yield but it proves that hyponitrous acid is a dioxide. The reaction proceeds as:

\( HO-NH_{2} + O=N-OH \rightarrow HO-N=N-OH + H_{2} O \)

Most noteworthy, we can prepare hyponitrous acid by the oxidation of hydroxylamine with \( CuO, HgO, Ag_{2} \) and by the oxidation of hydroxylamine with \( N_{2} O_{3} \) in methyl-alcoholic solution.

Properties of Hyponitrous Acid

Its regular alkali salts of the dibasic acid are soluble in water and are hydrolyzed, which gives alkaline solutions. Moreover, the normal salts of other bases are very slightly soluble. Like the free acids, the acid salts are very unstable.

Furthermore, in its dry state it decomposes at \( 100^{o}C \), giving \( AgNO_{3} \), and it explodes at \( 150^{o}C \). In nitric acid, alkalies dissolve and reprecipitate it. In addition, acetic acid and hydrogen sulfide set free hyponitrous acid and it decomposes by hot alkalies. Also, it reacts with alkyl iodides to give alkyl hyponitrites.