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Benzoyl peroxide

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Tube of Basiron, a water-based 5% benzoyl peroxide preparation for the treatment of acne.
A bleached fabric stain caused by contact with a benzoyl peroxide-based consumer product.

Benzoyl peroxide (Template:PronEng) is a chemical in the organic peroxide family. It consists of two benzoyl groups (benzoic acid with the H of carboxylic acid removed) joined by a peroxide group. Acceptable condensed structural formulae would include C6H5-COO-OOC-C6H5, PhCO-O-O-COPh, and (PhCO)2O2. It is often abbreviated Bz2O2.

Uses

Benzoyl peroxide is used as a radical initiator. Homolytic cleavage of the weak oxygen-oxygen bond forms benzoyl free radicals which trigger further reactions.

Jack Breitbart of Revlon laboratories first developed benzoyl peroxide's use for treating acne in the 1920s. It is typically placed over the affected areas in gel or cream form, in concentrations of 2.5% increasing through the usually effective 5% to up to 10%. Research suggests that 5 and 10% concentrations are not significantly more effective than 2.5% and 2.5% is usually better tolerated.[1][2] It commonly causes initial dryness and sometimes irritation, although skin tolerance usually occurs after a week or so. A small percentage of people are much more sensitive to it and liable to suffer burning, itching, peeling and possibly swelling[3]. It is sensible to apply the lowest concentration and build up as appropriate. Once tolerance is achieved, increasing the quantity or concentration a second time and gaining tolerance at a higher level usually gives better subsequent acne clearance. Benzoyl peroxide works as a peeling agent, increasing skin turnover and clearing pores, thus reducing the bacterial count there as well as directly as an antibacterial.

Other common uses for benzoyl peroxide include dying hair, and as an active ingredient in teeth whitening systems. It is also used in the preparation of flour, and can be used as an initiator and catalyst for polyester thermoset resins (as an alternative to the much more hazardous methyl ethyl ketone peroxide).

Adverse effects

In a 1977 study using a human maximization test, 76% of subjects acquired a contact sensitation to benzoyl peroxide. Formulations of 5% and 10% were used.[4]

Safety

Pure benzoyl peroxide is highly flammable, explosive, toxic and a possible tumor promoter and may act as a mutagen[5], and should be handled with care.

Diluted in an ointment, benzoyl peroxide is used as an acne treatment and the following precautions and claims pertain to this use. Attention should be paid to the safety directions provided when purchased.

In the United States, the typical concentration for benzoyl peroxide is 2.5% to 10% for both prescription and over the counter use in treatment for acne. Higher concentrations are used for hair bleach and teeth whitening. Benzoyl peroxide, like most peroxides, is a powerful bleaching agent. Contact with fabric (including clothing and bed linens) or hair 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.[citation needed]

Benzoyl peroxide breaks down in contact with skin, producing benzoic acid and oxygen, neither of which is significantly toxic.[6] It is important to note that the safety of the decomposition products does not mean that the substance itself is safe, as it is benzoyl peroxide's action as an oxidizing agent that is of importance. Hydrogen peroxide is corrosive, toxic and carcinogenic, but decomposes to form water and oxygen. Sodium hypochlorite (bleach) also shares these properties, but decomposes to form harmless products such as sodium chloride.

Synthesis

Benzoyl peroxide is usually prepared by reacting sodium peroxide with benzoyl chloride to give benzoyl peroxide and sodium chloride.

2 PhCOCl + Na2O2 → (PhCO)2O2 + 2 NaCl

Decomposition

The half-life of benzoyl peroxide is one hour at 92°C. At 131°C, the half-life is one minute. [7]

References

  1. ^ Mills, OH Jr (1986). "Comparing 2.5%, 5%, and 10% benzoyl peroxide on inflammatory acne vulgaris". International Journal of Dermatology. 25 (10): 664–667. doi:10.1111/j.1365-4362.1986.tb04534.x. PMID 2948929. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ Yong, CC (1979). "Benzoyl peroxide gel therapy in acne in Singapore". International Journal of Dermatology. 18 (6): 485–488. doi:10.1111/j.1365-4362.1979.tb01955.x. PMID 158569.
  3. ^ Typical product information leaflets and monographs
  4. ^ James J. Leyden, Albert M. Kligman (1977), "Contact sensitization to benzoyl peroxide", Contact Dermatitis 3 (5), 273–275. doi:10.1111/j.1600-0536.1977.tb03674.x
  5. ^ Safety (MSDS) data for benzoyl peroxide
  6. ^ "Benzoyl Peroxide" section 3.1.1
  7. ^ Hui Li (1998). "Synthesis, Characterization and Properties of Vinyl Ester Matrix Resins" (PDF). Retrieved 2007-02-17. {{cite journal}}: Cite journal requires |journal= (help)
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