Peroxide, benzoyl

Benzoyl peroxide is used mainly in acne treatment and is an irritant. Allergic contact dermatitis to this compound is not infrequent. Eaglstiein (1968) reported two cases. The sensitization rate has been estimated to be 1 %-2.5%. In a human maximization test, 76% became sensitized (Leyden and Kligman 1977). Crossreactions to benzoic acid and related compounds were not found. The drug has been advocated for treatment of chronic leg ulcers. Eight of 16 patients showed positive patch tests to 2% benzoyl peroxide after 6 weeks of leg ulcer treatment with 10% benzoyl peroxide (Jensen et al. 1980). Patients sensitized to benzoyl peroxide may be at risk in certain occupations (e.g., baking and the plastics industry). 

Synonyms dibenzoyl peroxide benzoyl ace-toxyl Benzac Oxylite Superox Lucidol 

Benzoyl peroxide is used as a source of free radicals in many organic syntheses and to initiate polymerizations of styrene, vinyl chloride, vinyl acetate, and acrylics to cure thermoset polyester resins and silicone rubbers in medicine for treating acne and for bleaching vegetable oil, cheese, flour, and fats. 

White granular powder, or crystals with faint odor mp 103-106 C (217.4-222.8 F), decomposes explosively density 1.334 at 25°C (77°F) sparingly soluble in water and alcohol dissolves readily in benzene, chloroform, and ether. 

The health hazard from benzoyl peroxide is low. It can cause irritation of the skin, mucous membranes, and eyes. An intraperi-toneal injection of 250 mg/kg was lethal to adult mice. Systemic toxicity in humans is not known. It may be mild to moderately toxic on an acute basis. The oral LD50 value in rats is 7710 mg/kg (NIOSH 1986). Its toxicity from inhalation is low an LC50 value of 700 ppm in mice is suggested (ACGIH 1986). 

Benzoyl peroxide may cause gene damage and DNA inhibition. It has been found to cause skin tumor. The evidence of its carcinogenicity in animals and humans is inadequate. 

Benzoyl chloride interacts with hydrogen peroxide in the presence of sodium hydroxide solution to give rise to benzoyl peroxide with the elimination of two moles of hydrochloric acid. The above reaction, being exothermic in nature, should be carried out in an ice-bath. The excess of sodium hydroxide present in the reaction mixture converts the unreacted benzoyl chloride into sodium benzoate and also reacts with liberated HCl to give sodium chloride. Thus, both sodium benzoate and NaCl being water-soluble remain in the solution, whereas the sparingly soluble benzoyl peroxide gets separated in the reaction mixture. 

5 Procedure. The various steps involved are stated below in a sequential manner  

The yield of crude benzoyl peroxide is approximately 11.2 g having mp 101-102.5°C. 

T Recrystallization. Recrystallize the crude product by dissolving in chloroform strictly at Room Temperature only and adding twice the volume of absolute methanol. 

Special Precautionary Note. Just like other Organic Peroxides, benzoyl peroxide may be handled with utmost care and restrain behind well-guarded shatter-proof screens and always horn or moulded polyethylene (Not Nickel or Stainless Steel) spatulas must be employed. It is an extremely Shock-Sensitive substance. 

By the reaction between a solution of an acyl halide in a dry organic solvent, such as toluene, with a cold solution of sodium peroxide, for example  

Perbenzoic acid. Treatment of a cold sodium methoxide solution with a solution of pure benzoyl peroxide in chloroform affords methyl benzoate and a solution of the sodium salt of perbenzoic acid  

The methyl benzoate is removed by extraction with chloroform, and upon cautious acidification of the aqueous layer perbenzoic acid is liberated the latter is extracted with chloroform and is usually preserved as a solution in this solvent  

Monoperphthalic acid. This is obtained by adding finely-powdered phthalic anhydride to a well-stirred solution of 30 per cent, hydrogen peroxide in alkali at —10° the solution is acidified and the per acid is extracted with ether  

To determine the exact peroxide content of benzoyl peroxide (and of other organic peroxides) the following procedure may be employed. Place about 0 05 g. of the sample of peroxide in a glass-stoppered conical flask add 5-10 ml. of acetic anhydride (A.R. or other pure grade) and 1 g. of powdered sodium iodide. Swirl the mixture to dissolve the sodium iodide and allow the solution to stand for 5-20 minutes. Add 50-75 ml. of water, shake the mixture vigorously for about 30 seconds, and titrate the liberated iodine with standard sodium thiosulphate solution using starch as indicator. 

2 02NC,H4C0C1 + NagOj — [p-OjNC.H COJjOj + 2NaCl 

2p-02NC,H4C0Cl + NaaOa — [p OaNC H4CO]aOa + 2NaCl 

To determine the exact peroxide content of benzoyl peroxide (and of other oi anic peroxides) the foUowing procedure may be employed. Place about 0-05 g. of the sample of peroxide in a glass-stoppered conical flask add 

EXTREME RISK OF EXPLOSION BY SHOCK, FRICTION, FIRE, OR OTHER SOURCE OF IGNITION 

White granulated crystals, normally supplied as moistened with about 30% water mp, 103-106°C (dec).1 

Highly flammable when dry explosive at elevated temperatures.2 

Insoluble in water and alcohol1-3 soluble in benzene, chloroform, and ether.1 Liable to explode when heated above melting point or when subjected to friction or shock when dry.3 Contact with metal should be avoided. 

Dry material burns readily and is sensitive to heat, shock, friction, or contact with combustible materials. It explodes above the melting point.4,5 Benzoyl peroxide should not be recrystallized from hot chloroform, but rather precipitated from cold chloroform with methanol.6 The peroxide should be stored in waxed paper tubs and never in metal or glass containers with screw-type closures.5 

Data were last reviewed in lARC (1985) and the compound was classified in lARC Monographs Supplement 7 (1987). 

94-36-0 Chem. Abstr. Name Dibcnzoyl peroxide RJPAC Systematic Name Benzoyl peroxide 

Synonyms Benzoic acid, peroxide benzoperoxide benzoyl superoxide diphenyl-glyoxal peroxide 

2 Structural and molecular formulae and relative molecular mass 

Production of benzoyl peroxide in the United States in 1982 was 2300 tonnes. Information available in 1995 indicated that it was produced in 16 countries (Chemical Information Services, 1995). 

White or off-white needle-shaped water-soluble crystals. 

Benzoyl peroxide is used as a bleaching agent in wheat flour, but its more familiar use is as a powerful acne medication that can lay claim to the following benefits  

A familiar peroxide is hydrogen peroxide. It has two oxygen atoms bound together, and each of those atoms in turn bind it to a hydrogen atom. 

Peroxides make good bleaches. The oxygen atoms combine with dyes to make the dyes colorless. This process, called oxidation, can kill germs. 

Fukuda K, Matsushita H, Sakahe H, et ah Carcinogenicity of henzyl chloride, henzal chloride, benzotrichloride and henzoyl chloride in mice hy skin application. Gann 72 655-664, 1981 

Stoner GD, You M, Morgan MA, et ah Lung tumor induction in strain A mice with hen-zotrichloride. Cancer Lett 33 167-73, 1986 

Fukuda K, Matsushita H, Takemoto K, et ah Carcinogenicity of henzotrichloride administered to mice hy gastric intubation. Ind Health 31 127-131, 1993 

I ARC Monographs on the evaluation of the carcinogenic risk of chemicals to humans, Vol 71, Re-evaluation of some organic chemicals, hydrazine and hydrogen peroxide, pp 453-77. Lyon, International Agency for Research on Cancer, 1999 

Synonyms Benzoyl superoxide dibenzoyl peroxide lucidol oxylite 

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Such reactions can be initiated by free radicals, derived from compounds (initiators) such as benzoyl peroxide, ammonium persulphate or azobis-isobutyronitrile or by ionic mechanisms... 

Such a mechanism is supported by the fact that the reaction is accelerated by benzoyl peroxide and other radical-producing agents. It is now however considered that the function of the A -bromosuceinimide is to provide a constant, very low concentration of molecular bromine (Tedder et al,). 

It is essential to use freshly recrystallised benzoyl peroxide. The commercial material usually gives poor results. Commercial benzoyl peroxide may bo recrystal, lised from a small amount of hot chloroform, or by dissolving in chloroform and precipitating with absolute methyl alcohol. 

The m.p. is not always a safe criterion of purity. Benzoyl peroxide may be analysed as follows -. Dissolve about 0-6 g., accurately weighed, of benzoyl peroxide in Is ml. of chloroform in a 350 ml. conical flask. Cool to — 5°, and add 25 ml. of 0- IN sodium methoxide solution at once with cooling and shaking. After 5 minutes at — 5°, add 100 ml. of iced water, 5 ml. of 10 per cent, sulphuric acid, and 2 g. of potassium iodide in 20 ml. of 10 per cent, sulphuric acid in the order mentioned with vigorous stirring. Titrate the liberated iodine with standard 0-lN sodium thiosulphate solution. 

Place 10 g. of hquid methyl methacrylate in a test-tube, add 10-20 mg. of benzoyl peroxide (Section IV, 196), stopper the test-tube loosely and heat in a boiling water bath. After 20-25 minutes, the hquid suddenly becomes very viscous and soon sets to a hard, colourless mass of the polymer. 

Heat 20 g. of styrene (Section IX,6) with 0 -2 g. of benzoyl peroxide (Section IV,196) on a water bath for 60-90 minutes. A glass-bke polymer (polystyrene) is produced. The polymer is soluble in benzene and in dioxan and can be precipitated from its solution by alcohol. 

They do, however, react readily, even in the dark, with sulphuryl chloride in the preaenoe of a trace of benzoyl peroxide as a catalyst (compare Section 1V,22). 

These results show that in the phenylation of thiazole with benzoyl peroxide two secondary reactions enter in competition the attack of thiazole by benzoyloxy radicals, leading to a mixture of thiazolyl benzoates, and the formation of dithiazolyle through attack of thiazole by the thiazolyl radicals resulting from hydrogen abstraction on the substrate and from the dimerization of these radicals. This last reaction is less important than in the case of thiophene but more important than in the case of pyridine (398). 

TABLE 1-56. TYPICAL PRODUCT DISTRIBUTION OF THE DECOMPOSITION AT 100°C OF BENZOYL PEROXIDE (0.02 MOLE) IN THIAZOLE (I MOLE) (397)... 

Benzoyl peroxide has been the most common source of phenyl radicals. But in reaction with thiazoles the benzoyloxy radical abstracts a hydrogen atom from the thiazole nucleus or from a methyl group in the case of methylthiazoles, giving by-products such as dithiazolyls or 2.2 -dithiazolylethane (183). The results obtained with benzoyl peroxide are summarized in Tables III-23, III-24. and III-25. 

TABLE irr-23. PHENYLATION OF THIAZOLE WITH BENZOYL PEROXIDE (183)... 

Concentration expressed in moles per mole of benzoyl peroxide used. 

TABLE 111-24. PRODUCTS FORMED BY THE DECOMPOSITION OF BENZOYL PEROXIDE IN THIAZOLE, 4-METHYLTHIAZOLE, AND 2.4-DIMETHYLTHIAZOLE WITH A MOLAR RATIO OF AND A REACTION TIME OF 20 hr AT 78°C (184)... 

The quantities of reactants and products are expressed in grams, the figures in parentheses are the yields in mole per mole of benzoyl peroxide. 

TABLE III-25. ACTTION OF BENZOYL PEROXIDE ON 4-METHYLTHlAZOLE AT 80°C UNDER NITROGEN MOLE OF PEROXIDE/MOLE OF THIAZOLE) (184. 185)... 

Benzoyl peroxide is a com monly used free radical ini tiator It has the formula O O... 

Polymerization of styrene is carried out under free radical conditions often with benzoyl peroxide as the initiator Figure 1111 illustrates a step m the growth of a poly styrene chain by a mechanism analogous to that of the polymerization of ethylene (Sec tion 6 21)... 

A certain compound A when treated with N bromosuccinimide and benzoyl peroxide under photochemical conditions in refluxing carbon tetrachloride gave 3 4 5 tnbromobenzyl bromide in excellent yield Deduce the structure of compound A... 

Benzoyl peroxide Direct sunlight, sparks and open flames, shock and friction, acids, alcohols, amines, ethers, reducing agents, polymerization catalysts, metallic naph-thenates... 

Polyethylene cross-linked by irradiation with high-energy electrons. Polysilicones cross-linked by reaction with benzoyl peroxide. 

Figure 6.3 Log-log plots of Rp versus concentration which verify the order of the kinetics with respect to the constituent varied, (a) Monomer (methyl methacrylate) concentration varied at constant initiator concentration. [Data from T. Sugimura and Y. Minoura, J. Polym. Sci. A-l 2735 (1966).] (b) Initiator concentration varied AIBN in methy methacrylate (o), benzoyl peroxide in styrene ( ), and benzoyl peroxide in methyl methacrylate ( ). (From P. J. Flory, Principles of Polymer Chemistry, copyright 1953 by Cornell University, used with permission.)...

Chlorine Benzoyl peroxide L-Ascorbic acid L-Cysteine... 

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