Hydrogen peroxide (H2O2)

It is also called as oxygenated water (H₂O – O)

In its pure form it is a colorless liquid, slightly more viscous than water

Structure: 

Hydrogen peroxide (H₂O₂) is a non-planar molecule. It has half opened book structure. Two oxygen atoms lying on spine of the book with O – O peroxy linkage and 2 ‘H’ atoms on each leaf of book.

The molecular structures of gaseous and crystalline H₂O₂ are significantly different. This difference is attributed to the effects of hydrogen bonding, which is absent in the gaseous state.
Preparation:

BaO₂.8H₂O + H₂SO₄ → H₂O₂ + BaSO₄↓ + 8H₂O

Na₂O₂ + H₂SO₄ → Na₂SO₄ + H₂O₂.

This is Merck’s process.

Hydrogen peroxide is prepared by hydrolysis of the ammonium peroxydisulfate, which was itself obtained via the electrolysis of a solution of ammonium bisulfate (NH₄HSO₄) in sulfuric acid.

 (NH₄)₂S₂O₈ + 2 H₂O → H₂O₂ + 2 (NH₄) HSO₄

Anthraquinone process:

Industrially it is prepared by the anthraquinone process, anthraquinone (such as 2-ethylanthraquinone or the 2-amyl derivative) is reduced to the corresponding anthrahydroquinone, typically via hydrogenation on a palladium catalyst.

The anthrahydroquinone then undergoes to autoxidation to regenerate the starting anthraquinone, with hydrogen peroxide being produced as a by-product (1%). Hydrogen peroxide is then extracted.

The anthraquinone derivative is reduced back to the dihydroxy (anthracene) compound using hydrogen gas in the presence of a metal catalyst. The cycle then repeats itself.

Chemical properties:

Acidic property:

Hydrogen peroxide is a week acid. In an aqueous solution it ionizes forming hydronium-ion and peroxide-ion:

H₂O₂ + H₂O ⇄ H₃O⁺ + O₂^2–

Oxidation-reduction properties:

Hydrogen peroxide acts as both an oxidizing and a reducing agent.

In acidic solution it is an oxidizing agent:

2KI + H₂O₂ + H₂SO₄ → I₂ + K₂SO₄ + 2H₂O

However both in basic and in a neutral solutions hydrogen peroxide can be an oxidizing agent:

Cr₂(SO₄)₃ + 3H₂O₂ + 10NaOH → 2Na₂CrO₄ + 3Na₂SO₄ + 8H₂SO₄

PbS + 4H₂O₂ → PbSO₄ + 4H₂O

At the presence of oxidizing agent it exhibits reduction properties in acidic, basic and neutral solutions:

Cl₂ + H₂O₂ → 2HCl  + O₂­;

Ag₂O + H₂O₂ → H₂O + O₂­ + 2Ag;

2KMnO₄ + 5H₂O₂ + 3H₂SO₄ → 2MnSO₄ + 5O₂ + K₂SO₄ + 8H₂O.

Decomposition of hydrogen peroxide:

Light, heating and the heavy metals hardly accelerate the process of hydrogen peroxide decomposition:

\(2{{H}_{2}}{{O}_{2}}\xrightarrow{Mn{{O}_{2}}}2{{H}_{2}}O+{{O}_{2}}\)

Uses:

• Its oxidizing properties are used in the bleaching of substances, such as hair, ivory, feathers, and delicate fabrics, which would be destroyed by other agents.
• It is used also medicinally, in the form of a 3% aqueous solution, as an antiseptic and throat wash.
• Hydrogen peroxide is used in restoring the original colors on paintings that have darkened through the conversion of the white lead used in the paintings to lead sulfide.
• The hydrogen peroxide oxidizes the black lead sulfide to white lead sulfate.
• It is used also as a source of oxygen in the fuel mixture for many rockets and torpedoes.
• It is used in synthesis of hydroquinone, tartaric acid and certain food products.