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Benzoyl peroxide
Identifiers
CAS number 94-36-0 Yes check.svgY
PubChem 7187
ChemSpider 6919
EC-number 202-327-6
RTECS number DM8575000
ATC code D10AE01,QD11AX90
SMILES
InChI
InChI key OMPJBNCRMGITSC-UHFFFAOYAV
Properties
Molecular formula C14H10O4
Molar mass 242.23 g mol−1
Appearance colourless solid
Density 1.334 g/cm3
Melting point

103–105 °C decomp.

Solubility in water poor
Hazards
MSDS External MSDS
EU Index 617-008-00-0
EU classification Explosive (E)
Irritant (Xi)
R-phrases R3, R7, R36, R43
S-phrases (S2), S3/7, S14, S36/37/39
NFPA 704
NFPA 704.svg
1
3
3
OX
Autoignition
temperature
80 °C
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references
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 (pronounced /ˈbɛnzɔɪl pəˈrɒksaɪd/) is an organic compound in the organic peroxide family. It consists of two benzoyl groups joined by a peroxide group. Its structural formula is [C6H5C(O)]2O2. It is one of the most important organic peroxides in terms of applications and the scale of its production. Benzoyl peroxide is used as an acne treatment, for improving flour, for bleaching hair and teeth, for polymerising polyester and many other uses.

Contents

Synthesis, structure, physical properties

Benzoyl peroxide was the first organic peroxide prepared by intentional synthesis. It was prepared by treating benzoyl chloride with barium peroxide,[1] a reaction that probably follows this stoichiometry:

2 C6H5C(O)Cl + BaO2 → [C6H5C(O)]2O2 + BaCl2

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

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

[C6H5C(O)]2O2 → 2C6H5CO2

The symbol indicates that the products are radicals, i.e. they contain an odd number of electrons. 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.[2]

Benzoyl peroxide breaks down in contact with skin, producing benzoic acid and oxygen, neither of which is significantly toxic.[3] 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 can be corrosive due to its oxidizing properties, but decomposes to form water and oxygen. Sodium hypochlorite (commonly known as "bleach") also shares these properties, but decomposes to form harmless products such as sodium chloride.[citation needed]

Uses

Most benzoyl peroxide is used as a radical initiator to induce polymerizations.[4] Other major applications include its antiseptic and bleaching properties.

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Acne treatment

Benzoyl peroxide for acne treatment is typically applied to 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.[5][6] It commonly causes initial dryness and sometimes irritation, although the skin develops tolerance 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. 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 antimicrobial.[citation needed]

Other uses

Other common uses for benzoyl peroxide include dyeing 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).[citation needed]

In the U. S., the typical concentration for benzoyl peroxide is 2.5% to 10% for both prescription and over the counter preparations that are used 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 fabrics 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]

Adverse effects

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.[7]

Safety

Unlike most organic compounds, benzoyl peroxide is potentially explosive and hence it can cause fires without external ignition. The hazard is acute for the pure material, and for this reason, in commerce the compound is usually used as a solution or a paste. For example, cosmetics contain only a few percent of benzoyl peroxide and thus pose no explosion risk.

References

  1. ^ Brodie, B. C. (1858), "Ueber die Bildung der Hyperoxyde organischer Säureradicale", Justus Liebigs Ann. Chem. 108: 79–83, doi:10.1002/jlac.18581080117 .
  2. ^ Li, Hui, III (1998), Synthesis, Characterization and Properties of Vinyl Ester Matrix Resins, Ph.D. Dissertation, University of Vermont, Chapter 2, http://scholar.lib.vt.edu/theses/available/etd-42198-113329/unrestricted/ch2.pdf .
  3. ^ Benzoyl peroxide, SIDS Initial Assessment Report, Geneva: United Nations Environment Programme, April 2004, http://www.inchem.org/documents/sids/sids/BENZOYLPER.pdf .
  4. ^ Klenk, Herbert; Götz, Peter H.; Siegmeier, Rainer; Mayr, Wilfried (2005), "Peroxy Compounds, Organic", Ullmann’s Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a19_199 .
  5. ^ Mills, O. H., Jr.; Kligman, A. M.; Pochi, P.; Comite, H. (1986), "Comparing 2.5%, 5%, and 10% benzoyl peroxide on inflammatory acne vulgaris", Int. J. Dermatol. 25 (10): 664–67, doi:10.1111/j.1365-4362.1986.tb04534.x, PMID 2948929 .
  6. ^ Yong, C. C. (1979), "Benzoyl peroxide gel therapy in acne in Singapore", Int. J. Dermatol. 18 (6): 485–88, doi:10.1111/j.1365-4362.1979.tb01955.x, PMID 158569 .
  7. ^ Leyden, James J.; Kligman, Albert M. (1977), Contact Dermatitis, 3, pp. 273–75, doi:10.1111/j.1600-0536.1977.tb03674.x .

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