Benzoyl peroxide

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

. The O=C-O-O dihedral angle is 90°. The O-O distance is 1.434 Å. The original 1858 synthesis by Liebig reacted benzoyl chloride with barium peroxide, a reaction that probably follows this equation: :2 C6H5C(O)Cl + BaO2 → (C6H5CO)2O2 + BaCl2 Benzoyl peroxide is usually prepared by treating hydrogen peroxide with benzoyl chloride under alkaline conditions. :2 C6H5COCl + H2O2 + 2 NaOH → (C6H5CO)2O2 + 2 NaCl + 2 H2O The oxygen–oxygen bond in peroxides is weak. Thus, benzoyl peroxide readily undergoes homolysis (symmetrical fission), forming free radicals: :(C6H5CO)2O2 → 2  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. In 1901, it was observed that the compound made the tincture of guaiacum tincture turn blue, a sign of oxygen being released. Around 1905, Loevenhart reported on the successful use of benzoyl peroxide 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 in 1929, and for sycosis vulgaris and acne varioliformis in 1934. It was officially approved for the treatment of acne in the US in 1960. such as for polyester and poly(methyl methacrylate) (PMMA) resins and dental cements and restoratives. It is also used in rubber curing and as a finishing agent for some acetate yarns. == Medical uses ==

Benzoyl peroxide is effective for treating acne lesions. It does not induce antibiotic resistance. unlike tezarotene and tretinoin. Combination products such as benzoyl peroxide/clindamycin and benzoyl peroxide/salicylic acid appear to be slightly more effective than benzoyl peroxide alone for the treatment of acne lesions. The combination tretinoin/benzoyl peroxide was approved for medical use in the United States in 2021. Benzoyl peroxide for acne treatment is typically applied to the affected areas in gel, cream, or liquid, in concentrations of 2.5% increasing through 5.0%, and up to 10%. In general, acne vulgaris is a hormone-mediated inflammation of sebaceous glands and hair follicles. Hormone changes cause an increase in keratin and sebum production, leading to blocked drainage. C. acnes has many lytic enzymes that break down the proteins and lipids in the sebum, leading to an inflammatory response. The free-radical reaction of benzoyl peroxide can break down the keratin, therefore unblocking the drainage of sebum (comedolytic). It can cause nonspecific peroxidation of C. acnes, making it bactericidal, Some evidence suggests that benzoyl peroxide has an anti-inflammatory effect as well. In micromolar concentrations it prevents neutrophils from releasing reactive oxygen species, part of the inflammatory response in acne. Because of these possible side effects, it is recommended to start with a low concentration and build up as appropriate, as the skin gradually develops tolerance to the irritation caused by the medication. Skin sensitivity typically resolves after a few weeks of continuous use. Irritation can also be reduced by avoiding harsh facial cleansers and wearing sunscreen prior to sun exposure. About one-third of people experience phototoxicity under exposure to ultraviolet (UVB) light. Dosage In the US, the typical concentration for benzoyl peroxide is 2.5% to 10% for both prescription and over-the-counter drug preparations that are used in treatment for acne. Other medical uses Benzoyl peroxide is used in dentistry as a tooth whitening product. ==Safety==

Explosion hazard Benzoyl peroxide is potentially explosive like other organic peroxides, and can cause fires without external ignition. The hazard is acute for the pure material, so the compound is generally used as a solution or a paste. For example, cosmetics contain only a small percentage of benzoyl peroxide and pose no explosion risk. Toxicity Benzoyl peroxide breaks down in contact with skin, producing benzoic acid and oxygen, neither of which is very toxic. The carcinogenic potential of benzoyl peroxide has been investigated. A 1981 study published in the journal Science found that although benzoyl peroxide is not a carcinogen, it does promote cell growth when applied to an initiated tumor. The study concluded, "caution should be recommended in the use of this and other free radical-generating compounds". A 1999 IARC review of carcinogenicity studies found no convincing evidence linking benzoyl peroxide acne medication to skin cancers in humans. However, some animal studies found that the compound could act as a carcinogen and enhance the effect of known carcinogens. Benzoyl peroxide can break down into carcinogen benzene at temperatures above 50 °C. Skin irritation In a 1977 study using a human maximization test, 76% of subjects acquired a contact sensitization to benzoyl peroxide. Formulations of 5% and 10% were used. The US National Institute for Occupational Safety and Health has developed criteria for a recommended standard for occupational exposure to benzoyl peroxide. Cloth bleaching Contact with fabrics or hair, such as from still-moist acne/pimple medication, can cause permanent color dampening almost immediately. Even secondary contact can cause bleaching, for example, contact with a towel that has been used to wash off benzoyl peroxide-containing hygiene products. == References ==