Benzoyl peroxide

Benzoyl peroxide
Skeletal formula
Ball-and-stick model
IUPAC name dibenzoyl peroxide
Other names benzoyl peroxide
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number	94-36-0 Y
PubChem	7187
ChemSpider	6919
EC-number	202-327-6
RTECS number	DM8575000
ATC code	D10AE01,QD11AX90
SMILES
InChI
InChI key	OMPJBNCRMGITSC-UHFFFAOYAV
style="background: #F8EABA; text-align: center;" colspan="2" | 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
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
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	75px 1 3 3 OX
Autoignition temperature	80 °C
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

File:Benzoyl peroxide gel.jpg

Tube of Basiron, a water-based 5% benzoyl peroxide preparation for the treatment of acne.

File:Benzoyl peroxide stain.jpg

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 peroxide family. It consists of two benzoyl groups bridged by a peroxide link. 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.

Benzoyl peroxide is included in the World Health Organization's "Essential Drugs List", which is a list of minimum medical needs for a basic health care system.

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, 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 → 2 C₆H₅CO₂^•

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.

Benzoyl peroxide breaks down in contact with skin, producing benzoic acid and oxygen, neither of which is significantly toxic. 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.

Uses

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

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 that 2.5% is usually better tolerated. 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.

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).

In the U. S., 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. 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.

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.

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.

External links

• International Chemical Safety Card 0225
• NIOSH Pocket Guide to Chemical Hazards 0052
• SIDS Initial Assessment Report from the Organisation for Economic Co-operation and Development (OECD)
• "Benzoyl peroxide", Re-evaluation of Some Organic Chemicals, Hydrazine and Hydrogen Peroxide (PDF), IARC Monographs on the Evaluation of Carcinogenic Risks to Humans 71, Lyon, France: International Agency for Research on Cancer, 1999, pp. 345–58, ISBN 92-832-1271-1 .
• Benzoyl Peroxide

cs:Benzoylperoxid zh:过氧化苯甲酰