Hydrogen peroxide

Chemical properties

Hydrogen peroxide can decompose spontaneously into water and oxygen. It usually

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acts as an oxidizing agent, but there are many reactions where it acts as a reducing agent, releasing oxygen as a by-product. It also readily forms both inorganic and organic peroxides.

Related Topics:
Oxidizing agent - Peroxide

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Decomposition

Hydrogen peroxide often decomposes exothermically into water and oxygen gas spontaneously:

Related Topics:
Exothermic - Water - Oxygen - Spontaneously

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:2 H2O2 → 2 H2O + O2 + Energy

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This process is very favourable; it has a ΔH° of -98.2 kJ/mol and a ΔG° of -119.2 kJ/mol. The rate of decomposition is dependent on the temperature concentration of the peroxide, as well as the pH and the presence of impurities and stabilizers. Hydrogen peroxide is incompatible with many substances which catalyse its decomposition, including most of the transition metals and their compounds. Common catalysts include manganese dioxide, potassium permanganate and silver. The same reaction is catalysed by the enzyme catalase, found in the liver, whose main function in the body is the removal of toxic byproducts of metabolism and the reduction of oxidative stress. The decomposition occurs more rapidly in alkali, so acid is often added as a stabilizer.

Related Topics:
ΔH° - KJ - Mol - ΔG° - PH - Catalyse - Transition metals - Manganese dioxide - Potassium permanganate - Silver - Enzyme - Catalase - Liver - Metabolism - Oxidative stress - Alkali - Acid

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Spilling high concentration peroxide on a flammable substance can cause an immediate fire fueled by the oxygen released by the decomposing hydrogen peroxide. High strength peroxide (also called high-test peroxide, or HTP) must be stored in a vented container to prevent the buildup of oxygen gas which would otherwise lead to the eventual rupture of the container. Any container must be made of a compatible material such as PTFE, polyethylene or aluminium (not stainless steel) and undergo a cleaning process (passivation) to remove all contamination prior to the introduction of peroxide. (Note that whilst compatible at room temperature, polyethylene can explode with peroxide in a fire.)

Related Topics:
Compatible - PTFE - Polyethylene - Passivation

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In the presence of certain catalysts, such as {{Iron}}2+ or {{Titanium}}3+, the decomposition may take a different path, with free radicals such as HO· (hydroxyl) and HOO· being formed. A combination of H2O2 and Fe2+ is known as Fenton's reagent.

Related Topics:
Hydroxyl - Fenton's reagent

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Redox reactions

In aqueous solution, hydrogen peroxide can oxidize or reduce a variety of inorganic ions. When it acts as a reducing agent, oxygen gas is also produced. In acid solution {{Iron}}2+ is oxidized to Fe3+,

Related Topics:
Oxygen - Acid

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:2 Fe2+(aq) + H2O2 + 2 H+(aq) → 2 Fe3+(aq) + H2O(l)

Related Topics:
Aq - H⁺ - L

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and sulfite (SO32−) is oxidized to sulfate (SO42−). However potassium permanganate is reduced to {{Manganese}}2+ by acidic H2O2. Interestingly under alkaline conditions some of these reactions reverse; Mn2+ is oxidized to Mn4+ (as MnO2), yet Fe3+ is reduced to Fe2+.

Related Topics:
Sulfite - Sulfate - Potassium permanganate - Alkaline - MnO₂

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:2 Fe3+ + H2O2 + 2 OH− → 2 Fe2+ + 2 H2O + O2

Related Topics:
OH⁻ - O₂

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Hydrogen peroxide is frequently used as an oxidising agent in organic chemistry. One application is for the oxidation of thioethers to sulfoxides.{{an|thioether}} For example methyl phenyl sulfide was oxidised to methyl phenyl sulfoxide in 99% yield in methanol in 18 hours (or 20 minutes using a TiCl3 catalyst):

Related Topics:
Oxidising agent - Thioether - Sulfoxide - Methyl - Phenyl - TiCl₃

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:Ph-S-CH3 + H2O2 → Ph-S(O)-CH3 + H2O

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Alkaline hydrogen peroxide is used for epoxidation of electron-deficient alkenes such as acrylic acids, and also for oxidation of alkylboranes to alcohols, the second step of hydroboration-oxidation.

Related Topics:
Epoxidation - Acrylic acid - Alkylborane - Alcohol - Hydroboration-oxidation

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Formation of peroxide compounds

Hydrogen peroxide is a weak acid, and it can form hydroperoxide or peroxide salts or derivatives of many metals. For example, with aqueous solutions of chromic acid (CrO3) it can form an unstable blue peroxide CrO(O2)2. It can also produce peroxoanions by reaction with anions; for example reaction with borax leads to sodium perborate, a bleach used in laundry detergents:

Related Topics:
Hydroperoxide - Peroxide - Salt - Chromic acid - Anion - Borax - Sodium perborate

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:Na2B4O7 + 4 H2O2 + 2 NaOH → 2 Na2B2O4(OH)4 + H2O

Related Topics:
Na₂B₄O₇ - NaOH - Na₂B₂O₄(OH)₄

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H2O2 converts carboxylic acids (RCOOH) into peroxy acids (RCOOOH), which are themselves used as oxidizing agents. Hydroen preoxide reacts with acetone to form acetone peroxide and it interacts with ozone to form hydrogen trioxide. Reaction with urea produces carbamide peroxide, used for whitening teeth. An acid-base adduct with triphenylphosphine oxide is a useful "carrier" for H2O2 in some reactions.

Related Topics:
Carboxylic acid - Acetone - Acetone peroxide - Ozone - Hydrogen trioxide - Urea - Carbamide peroxide - Triphenylphosphine oxide

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Basicity

Hydrogen peroxide is a much weaker base than water, but it can still form adducts with very strong acids. The superacid HF/SbF5 forms unstable compounds containing the (H3O2)+ ion.

Related Topics:
Base - Superacid - HF - SbF₅

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