HYDROGEN PEROXIDE (H2O2): STRUCTURE, PROPERTIES, USES, OBTAINING - CHEMISTRY - 2025

The hydrogen peroxide is an inorganic compound with the chemical formula H ₂ O ₂. Of all, it is the simplest peroxide of this family of chemical compounds. Its structural formula is HOOH, this internal oxygenated bridge being characteristic for all peroxides.

In 1818, H ₂ O ₂ was identified by Louies Jacques Thénard, who prepared a chemical compound which he then called hydrogen peroxide. It is an unstable compound, it decomposes on exposure to light, heat and some metals.

Chemical formula of hydrogen peroxide

It is a very useful compound that is used in the disinfection of minor wounds, hair whitening, water treatment, etc. Although it can have harmful actions for humans, it is found in all eukaryotic cells of living beings, where it performs several beneficial functions.

Hydrogen peroxide produces the oxidation of toxic substances such as phenols, ethanol, formaldehyde, etc., products that are eliminated by the liver and kidneys. In addition, it contributes to the destruction of bacteria phagocytosed by neutrophilic leukocytes and macrophages.

Structure

Molecule

Hydrogen peroxide molecule represented by a ball-and-stick model. Source: Benjah-bmm27 via Wikipedia.

The upper image shows the structure of the H ₂ O ₂ (HOOH) molecule, with the red spheres corresponding to the oxygen atoms, and the white ones the hydrogen atoms. Note that the molecule is not flat, and that the H atoms are not eclipsed in space (opposite each other).

Interestingly, H ₂ O ₂ finds it difficult to rotate its central simple bond OO, so the positions of these H's cannot be exchanged; one will not go down while the other goes up.

Why? Because in the two oxygen atoms there are two free pairs of electrons, which gives a total of eight very close electrons and which repel each other due to their negative charges.

Rotations

Yet the OO link is susceptible to slight rotation due to interactions with its environment.

For example, by bringing the two thumbs together, with the index fingers extended and the others closed, as if drawing a court, and then rotating the thumbs in such a way that one of the index fingers points forward and the other back, you will have a approximate representation of H ₂ O ₂.

If a body touches any of the index fingers, the thumbs will rotate in response to this interaction; however, they will immediately return to their original position due to the electronic repulsions mentioned above. These rotations thus frame the dynamic aspects of this molecule.

Intermolecular interactions

In the liquid state, H ₂ O ₂ manages to establish hydrogen bonds (HOOH-O ₂ H ₂), since otherwise its high boiling point (150 ºC) in comparison to that of water would not be explained.

Once it passes into the gas phase, the H ₂ O ₂ molecules presumably can no longer form such bridges, due not only to the greater intermolecular distance, but also the hydrogen atoms would be the first to touch in case of collisions (this can visualized again using the finger model).

Meanwhile, in the solid phase, the angle of the planes established by the H is 90º (put the index fingers perpendicular). Now the hydrogen bonds become even more important and the H ₂ O ₂ molecules are arranged in a crystal with a tetragonal structure.

Properties

sBottle with hydrogen peroxide. In pharmacies it is achieved with a concentration of 3% m / v. Source: Pixnio.

Names

-Hydrogen peroxide

-Dioxidan

-Oxidanol

-Perhydroxic acid

-O-hydroxyol

-Peroxide

Molar mass

34.0147 g / mol

Physical appearance

Pale blue (concentrated) or colorless liquid. It is slightly more viscous and dense than water. It is distilled for safety at low temperatures and at reduced pressure, since it decomposes on heating in an explosive form.

Odor

Sharp or ozone-like odor.

Taste

Bitter

Density

Solid 1.71 g / cm ³

The densities of its aqueous solutions depend on their concentration; for example, at 27% it has a density of 1.10 g / cm ³, while at 50%, 1.13 g / cm ³

Melting point

- 0.43 ºC

Boiling point

150.2 ° C. This value has been obtained by extrapolation, since hydrogen peroxide decomposes at high temperatures.

Water solubility

Miscible ≥ 100 mg / mL at 25 ºC

Solubility

It is soluble in ether and alcohols, but insoluble in petroleum ether. It decomposes into water and oxygen in many organic solvents.

Octanol / water partition coefficient

Log P = - 0.43

Vapor pressure

5 mmHg at 30 ° C.

Dissociation constant

pKa = 11.72

pH

Hydrogen peroxide solutions are slightly acidic. For example, a 35% one has a pH of 4.6; but when concentrated at 90%, the pH becomes less acidic: 5.1.

Refractive index (n

1,4061

Viscosity

1,245 cPoise at 20 ° C.

Heat capacity

1,267 J / gK (gas)

2,619 J / gK (liquid)

Heat of vaporization

1,519 J / g K

Stability

Stable under recommended conditions. It is further stabilized by the addition of acetanilide and tin salts.

Corrosion

Corrosive

Decomposition

It decomposes on exposure to light or in the presence of oxidizing and reducing substances. It also decomposes on heating. When it decomposes, it releases water and oxygen, and is favored by an increase in pH and temperature, as well as by the presence of the enzyme catalase.

Surface tension

80.4 dynes / cm at 20 ° C

Reactivity

H ₂ O ₂ acts as an oxidizing agent in acid solutions of ferrous iron (Fe ²⁺) to ferric iron (F ³⁺); it also oxidizes the sulfite ion (SO ₃ ^2-) to sulfate ion (SO ₄ ^2-).

It can also act as a reducing agent in the presence of basic solutions, reducing sodium hypochlorite (NaOCl) and potassium permanganate (KMnO ₄) with the release of oxygen.

Applications

Whitening

Hydrogen peroxide is used in the paper industry in pulp and paper bleaching, which consumes most of its annual production.

Disinfectant

Hydrogen peroxide is a mild antiseptic to prevent infection of small wounds, scrapes, and burns. It is also used as a mouthwash and to relieve mild irritation of the mouth due to the presence of canker sores or gingivitis.

It is also used to disinfect surfaces, the interior of refrigerators, water and combat excessive bacterial growth in water systems and cooling towers. Hydrogen peroxide releases free oxygen radicals, which break down pollutants.

Detergent

Hydrogen peroxide is used in the manufacture of laundry bleaching detergents, including sodium percarbonate. This compound is a complex of sodium carbonate and hydrogen peroxide that, when dissolved in water, separates into its components.

Cosmetic application

Diluted hydrogen peroxide is used in hair bleaching, prior to staining. It is also used to whiten teeth, as well as part of a homemade toothpaste.

Propellant

Hydrogen peroxide is used as the monopropellant or oxidizing component of a bipropolent rocket. It decomposes releasing oxygen and water, a characteristic that allowed its use as a propellant.

It is pumped into a reaction cell with the presence of a catalyst that accelerates said decomposition. During this, a high temperature water vapor is produced.

When the steam is expelled through a gap, it produces an impulse. The V-80 submarine, built in 1940, used oxygen generated from hydrogen peroxide in its turbines; called Walter's turbine system.

Obtaining

Initially, hydrogen peroxide was obtained industrially by hydrolysis of ammonium persulfate, or electrolysis of ammonium bisulfate, NH ₄ HSO ₄.

Hydrogen peroxide is currently obtained industrially through the use of anthraquinone. The process is carried out in four stages: hydrogenation, filtration, oxidation, extraction and purification.

Hydrogenation

The alkylanthroquinone is hydrogenated by passing the hydrogen gas through a hydrogenator loaded with alumina and a small amount of the catalyst (palladium). The temperature is kept at 45ºC with permanent stirring.

The alkyldroquinone is converted to the alkyl anthrahydroquinone and the tetrahydroalkylanthrahydroquinone, the latter being selected for its convenience for the following procedures.

Filtration

The solution containing the hydrogenated anthraquinone is filtered to remove traces of the catalyst it may contain.

Oxidation

The filtered solution is oxidized by passing air through it, forming low purity hydrogen peroxide.

Extraction and purification

The hydrogen peroxide solution passes through a liquid-liquid extraction column. Water flows through the column, while the hydrogen peroxide solution is pumped through it.

The water reaches the bottom of the extractor with a hydrogen peroxide concentration between 25 and 35% w / w. Then, it is purified by vacuum distillation, up to a hydrogen peroxide concentration of 30%. Finally it stabilizes and is stored.

Risks

Hydrogen peroxide burn. Source: Bobjgalindo

Hydrogen peroxide is a corrosive agent, so on contact with the skin it produces severe irritation, in addition to temporary whitening (top image). It can also cause eye damage, itching, a rash, redness, and blistering.

Inhalation causes irritation to the nose, throat and lungs. Meanwhile, repeated exposure can cause bronchitis, cough, phlegm and shortness of breath. And as if it weren't enough, it also generates headaches, dizziness, nausea and vomiting.

Severe exposure to hydrogen peroxide can cause fluid to build up in the lungs, known as pulmonary edema - a serious condition that requires prompt medical attention.

The Occupational Safety and Health Administration (OSHA) has established the maximum allowable for hydrogen peroxide of 1 ppm in a work environment in an 8-hour shift. However, as it is a mutagenic compound, exposure should be kept to a minimum.

References

1. Shiver & Atkins. (2008). Inorganic chemistry. (Fourth edition). Mc Graw Hill.
2. Wikipedia. (2019). Hydrogen peroxide. Recovered from: en.wikipedia.org
3. William R. Busing and Henri A. Levy. (2004). Crystal and Molecular Structure of Hydrogen Peroxide: A Neutron ‐ Diffraction Study. doi.org/10.1063/1.1696379
4. National Center for Biotechnology Information. (2019). Hydrogen peroxide. PubChem Database. CID = 784. Recovered from: pubchem.ncbi.nlm.nih.gov
5. The Editors of Encyclopaedia Britannica. (November 27, 2018). Hydrogen peroxide. Encyclopædia Britannica. Recovered from: britannica.com
6. New Jersey Department of Health. (2016). Hydrogen Peroxide.. Recovered from: nj.gov
7. Mathews, CK, Van Holde, KE, Ahern, KG (2002). Biochemistry. Third edition. Publisher Pearson Addison Wesley
8. Web MD. (2019). Hydrogen peroxide. Recovered from: webmd.com