The peroxide group refers to an oxygen–oxygen single bond (–O–O–) present in certain compounds, which are collectively known as peroxides. Examples include hydrogen peroxide (H₂O₂) and dibenzoyl peroxide (C₆H₅COO)₂​. ^[1,2]

Peroxides are widely used in industrial, environmental, and laboratory contexts owing to their strong oxidizing ability.

Classification ^[1,2]

Peroxides are broadly classified as inorganic or organic depending on the nature of the groups bonded to the peroxide (–O–O–) linkage.

1. Inorganic Peroxides

In inorganic peroxides, the bonded oxygen atoms of the peroxide linkage (–O–O–) are associated either with metal cations as the peroxide ion (O₂^2–) in ionic peroxides or with non-carbon atoms through covalent bonds.

The simplest inorganic peroxide is hydrogen peroxide (H–O–O–H), in which two hydrogen atoms are covalently bonded to the peroxide unit. Typical ionic peroxides include sodium peroxide (Na₂O₂) and barium peroxide (BaO₂).

Many inorganic peroxides are thermally unstable and readily decompose, evolving oxygen. They occur in different physical states, such as liquids (e.g., H₂O₂) and crystalline solids (e.g., Na₂O₂), and are widely used as disinfectants and bleaching agents. Their reactivity is strongly influenced by catalysts, temperature, light, and impurities.

Chemical Reactions

Hydrolysis:

Na₂O₂ + 2 H₂O → 2 NaOH + H₂O₂

Reaction with Carbon Dioxide:

2 Na₂O₂ + 2 CO₂ → 2 Na₂CO₃ + O₂

Redox Reaction:

3 Na₂O₂ + 2 Fe → Fe₂O₃ + 3 Na₂O

Thermal Decomposition:

2 Na₂O₂ → 2 Na₂O + O₂

2. Organic Peroxides

Organic peroxides contain the –O–O– linkage between carbon-containing groups. Several subclasses exist depending on the substituents attached to the peroxide bond, including dialkyl peroxides (RO–OR’), hydroperoxides (ROOH), organic peroxy acids (RCO₃H), and peresters (RCO₃R’).

The O–O bond is relatively weak. Consequently, organic peroxides are highly reactive and thermally unstable. They function as powerful oxidizing agents and readily undergo homolytic cleavage to generate free radicals. As a result, they are extensively used as polymerization initiators and cross-linking agents. Most organic peroxides are colorless liquids or white solids that are typically insoluble in water but soluble in organic solvents.

Chemical Reactions

Homolytic Cleavage:

(C₆H₅COO)₂ → 2 C₆H₅COO·

C₆H₅COO· → C₆H₅· + CO₂

Epoxidation:

Cyclohexane + m–C →

C₆H₁₀ + m−ClC₆H₄CO₃H → C₆H₁₀O + m−ClC₆H₄CO₂H

Reduction:

(CH₃)₃COOH + 2 I⁻ + 2 H⁺ → (CH₃)₃COH + I₂ + H₂O

Thermal Decomposition:

(CH_3​)₃​COOC(CH₃​)₃​ → 2(CH₃​)₃​CO⋅

(CH_3​)₃​CO⋅ → (CH₃​)₂​CO + CH₃​⋅

Uses ^[3,4]

• As a bleaching agent, it whitens textiles, paper pulp, and hair without forming chlorinated by-products.
• As a disinfectant and antiseptic, it destroys bacteria, fungi, and viruses in wound care, oral rinses, and surface sterilization.
• As an environmental oxidant, it oxidizes dyes, phenols, and odor-causing sulfides in water and wastewater treatment.
• As a synthetic oxidant, it acts as an oxygen donor in organic and inorganic oxidations such as epoxidation and hydroxylation.
• As a polymerization initiator and curing agent, it generates free radicals that initiate polymerization and cure or cross-link plastics, resins, and rubbers.
• As an analytical and laboratory reagent, it is used in redox titrations, oxygen generation, and the preparation of peroxo compounds and metal–peroxo complexes.

Peroxides occupy a central role in chemistry because the O–O linkage imparts a characteristic reactivity that underlies their behavior as oxidants and radical sources. This versatility enables applications ranging from disinfection and environmental remediation to polymer manufacture and synthetic oxidation processes.