Hyponitrous Acid Formula

Hyponitrous acid is an isomer of nitramide with the chemical formula H₂N₂O₂. It is a chemical compound whose IUPAC name is (E)-dihydroxydiazene. This acid is also called a hyponitrous acid dimer. Colorless crystals of hyponitrous acid are formed from ether solutions which readily decompose explosively when heated. The two series of salts formed by hyponitrous acid are the “hyponitrites,” which contain the [ON=NO]²⁻ anion, and the other one is the “acid hyponitrites,” which contain the [HON=NO]⁻ anion. This acid has two possible structures, i.e., trans-hyponitrous acid and cis-hyponitrous acid, where its trans form is more stable. The Cis of the acid form is unknown but its sodium salt can be obtained. The white crystals of trans-hyponitrous acid become explosive when dry. This acid plays a key role in enzymology, where a hyponitrite reductase enzyme catalyzes the chemical reaction.

Preparation of Hyponitrous Acid

• trans-hyponitrous acid is synthesized when Silver(I) hyponitrite is treated with an anhydrous HCl in the ether. A solid hyponitrous acid is formed after the evaporation of the ether. It is a weak dibasic acid (pKa₁ = 7.21, pKa₂ = 11.54) and an explosive compound.

Ag₂N₂O₂ + 2HCl → H₂N₂O₂ + 2AgCl

The acid decomposes into nitrous oxide and water in an aqueous solution with a half-life of 16 days at 25 °C at pH 1–3.

H₂N₂O₂ → H₂O + N₂O

Though N₂O is formally an anhydride of H₂N₂O₂, the acid cannot be prepared from the reaction of N₂O and water.

• Hyponitrous acid can also be produced from hydroxylamine and nitrous acid.

NH₂OH + HNO₂ → H₂N₂O₂ + H₂O

• We can also synthesize hyponitrous acid by the oxidation of hydroxylamine with HgO.

2NH₂OH + 2HgO → H₂N₂O₂ + 2Hg + 2H₂O

Structure of Hyponitrous Acid

The molecular or chemical formula of hyponitrous acid is H₂N₂O₂. Its linear formula is HON=NOH and its SMILES (Simplified molecular-input line-entry system) form is N(=NO)O. This acid has two possible structures, i.e., trans-hyponitrous acid and cis-hyponitrous acid.

Properties of Hyponitrous Acid 

Chemical Formula	H2N2O2
IUPAC name	(E)-dihydroxydiazene
Molar mass/Molecular weight	62.0282 g/mol
Appearance	white crystals
Conjugate base	Hyponitrite
Hydrogen bond acceptors	4
Hydrogen bond donors	2

Other Experimental properties and reactions

•  Hyponitrous acid reacts with the oxygen in the air and produces nitric and nitrous acids.

H₂N₂O₂ + 3O₂ → 2HNO₃ + 2HNO₂

• Hyponitrous acid reacts with hydrogen chloride (HCl) and atomic hydrogen (H₂) and produces hydrazinium chloride (N₂H₅Cl) and water.

H₂N₂O₂ + HCl + 3H₂ → N₂H₅Cl + 2H₂O

• Hyponitrous acid decomposes into nitrous oxide and water in an aqueous solution.

H₂N₂O₂ → H₂O + N₂O

• When hyponitrous acid reacts with potassium permanganate and sulfuric acid solution, manganese(II) sulfate, nitric acid, potassium sulfate, and water are produced.

5H₂N₂O₂ + 8KMnO₄ + 12H₂SO₄ → 8MnSO₄ + 10HNO₃ + 4K₂SO₄ + 12H₂O

Uses of Hyponitrous Acid

• The hyponitrous acid plays a key role in enzymology, where a hyponitrite reductase enzyme catalyzes the chemical reaction.

Hazards

• The white crystals of trans-hyponitrous acid become explosive when dry. 

FAQs on Hyponitrous Acid 

Question 1: What is hyponitrous acid?

Answer: 

Hyponitrous acid is an isomer of nitramide with the chemical formula H₂N₂O₂. This acid has two possible structures, i.e., trans-hyponitrous acid and cis-hyponitrous acid.

Question 2: Mention the number of hydroxyl groups present in hyponitrous acid.

Answer:

The chemical formula of hyponitrous acid is H₂N₂O₂ while its structure is OH-N=N-OH. From the structure of the hyponitrous acid, we can observe that two hydroxyl groups are present on either side of both nitrogen atoms. So, the number of hydroxyl groups present in hyponitrous acid is two.

Question 3: How is hyponitrous acid prepared?

Answer:

• Silver(I) hyponitrite and anhydrous HCl in the ether are used to synthesize trans-hyponitrous acid.

Ag₂N₂O₂ + 2HCl → H₂N₂O₂ + 2AgCl

• Hyponitrous acid reacts with hydrogen chloride (HCl) and atomic hydrogen (H₂) and produces hydrazinium chloride (N₂H₅Cl) and water.

H₂N₂O₂ + HCl + 3H₂ → N₂H₅Cl + 2H₂O

Question 4: Mention some properties of hyponitrous acid.

Answer:

The preferred IUPAC name of hyponitrous acid is (E)-dihydroxydiazene. Its chemical formula is H₂N₂O₂ and its molecular weight or molar mass is 62.0282 g/mol. Its conjugate is hyponitrite and occurs as white crystals in its trans-form.

Question 5: Mention some applications of hyponitrous acid.

Answer:

The hyponitrous acid plays a key role in enzymology, where a hyponitrite reductase enzyme catalyzes the chemical reaction.

Question 6: What happens when hyponitrous acid reacts with oxygen?

Answer:

Hyponitrous acid reacts with the oxygen in the air and produces nitric and nitrous acids.

H₂N₂O₂ + 3O₂ → 2HNO₃ + 2HNO₂