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Concept
Peroxyde de benzoyle
Résumé
Benzoyl peroxide is a chemical compound (specifically, an organic peroxide) with structural formula , often abbreviated as (BzO)2. In terms of its structure, the molecule can be described as two benzoyl (, Bz) groups connected by a peroxide (). 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, but it is principally used as in the production of polymers.
Benzoyl peroxide is mainly used in production of plastics and for bleaching flour, hair, plastics and textiles, as well as for acne treatment.
The original 1858 synthesis by Liebig reacted benzoyl chloride with barium peroxide, a reaction described by the following idealized equation:
Benzoyl peroxide is usually prepared by treating hydrogen peroxide with benzoyl chloride under alkaline conditions.
As in many other peroxides, the C-O-O-C linkage has a dihedral angle near 90°.
The oxygen–oxygen bond in peroxides is weak, although this weakness is not indicated by the O-O bond distance. Thus, benzoyl peroxide undergoes homolysis (symmetrical fission), forming free radicals:
The symbol • indicates that the products are radicals; i.e., they contain at least one unpaired electron. Such species are highly reactive. The homolysis is usually induced by heating. The half-life of benzoyl peroxide is one hour at 92 °C. At 131 °C, the half-life is one minute.
It has long been known that the compound has oxidizing properties. This property led to the use of BPO to treat various skin conditions, including burns, chronic varicose leg tumors, and tinea sycosis. He also reported animal experiments that showed the relatively low toxicity of the compound.
Treatment with benzoyl peroxide was proposed for wounds by Lyon and Reynolds in 1929, and for sycosis vulgaris and acne varioliformis by Peck and Chagrin in 1934. However, preparations were often of questionable quality. It was officially approved for the treatment of acne in the US in 1960.
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