Benzoyl peroxide

Benzoyl peroxide is a chemical compound (specifically, an organic peroxide) with the structural formula (C₆H₅−C(=O)O−)₂, often abbreviated as (BzO)₂. In terms of its structure, the molecule can be described as two benzoyl (C₆H₅−C(=O)−, Bz) groups connected by a peroxide (−O−O−). It is a white granular solid with a faint odour of benzaldehyde, poorly soluble in water but soluble in acetone, ethanol, and many other organic solvents. Benzoyl peroxide is an oxidizer, which is principally used in the production of polymers.

Benzoyl peroxide is mainly used in production of plastics and for bleaching flour, hair, plastics and textiles.

As a bleach, it has been used as a medication and a water disinfectant.

As a medication, benzoyl peroxide is mostly used to treat acne, either alone or in combination with other treatments. Some versions are sold mixed with antibiotics such as clindamycin. It is on the World Health Organization's List of Essential Medicines. It is available as an over-the-counter and generic medication. It is also used in dentistry for teeth whitening. In 2021, it was the 284th most commonly prescribed medication in the United States, with more than 700,000 prescriptions.

Benzoyl peroxide was first prepared and described by Justus von Liebig in 1858. Donald Holroyde Hey FRS (12 September 1904 – 21 January 1987) was a Welsh organic chemist who inferred that the decomposition of benzoyl peroxide generated free phenyl radicals.

The original 1858 synthesis by Liebig reacted benzoyl chloride with barium peroxide, a reaction that probably follows this equation:

Benzoyl peroxide is usually prepared by treating hydrogen peroxide with benzoyl chloride under alkaline conditions.

The oxygen–oxygen bond in peroxides is weak. Thus, benzoyl peroxide readily undergoes homolysis (symmetrical fission), forming free radicals: