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Wednesday, 03 August 2011 06:23

Peroxides, Organic and Inorganic

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The characteristic chemical structure of peroxides is the presence of two oxygen molecules that are linked together by a single covalent bond (peroxy compounds). This structure is inherently unstable. Peroxides will decompose readily into highly reactive free radicals.The negatively charged peroxide ion serves as an initiatior of many chemical reactions. This reactivity is a key to the usefulness of some peroxides in industry and also to the safety hazards which they may present.


Organic peroxides are most widely used in the chemical, plastics and rubber industries. They act as initiators for free-radical polymerizations of monomers to thermoplastic polymers and as agents for curing thermoset polyester resins and cross-linking elastomers and polyethylene. Organic peroxides are used as free-radical sources in many organic syntheses.

2-Butanone peroxide is a hardening agent for fibreglass and reinforced plastics, and a curing agent for unsaturated polyester resins. Cyclohexanone peroxide is a catalyst for the hardening of certain fibreglass resins; a bleaching agent for flour, vegetable oils, fats and waxes; as well as a polymerization agent in the plastics industry and a curing agent in the rubber industry. Dilauroyl peroxide finds use in the cosmetics and pharmaceutical industries and as a burn-out agent for acetate yarns. In addition to serving as a polymerization catalyst, tert-butyl peroxide acts as an ignition accelerator for diesel fuels.

Benzoyl peroxide is primarily used in the polymer industry to initiate free-radical polymerizations and copolymerizations of vinyl chloride, styrene, vinyl acetate and acrylics. It is also utilized for curing thermoset polyester resins and silicone rubbers and for hardening certain fibreglass resins. Benzoyl peroxide is used in medicine for the treatment of acne. It is the preferred bleaching agent for flour, and has been used for bleaching cheese, vegetable oils, waxes, fats and so on. Cumene hydroperoxide is used for the manufacture of phenols and acetone. Peracetic acid is a bactericide and a fungicide used especially in food processing. It also functions as a bleaching agent for textiles, paper, oil, waxes and starch, and as a polymerization catalyst.

Hydrogen peroxide has numerous uses, most of which derive from its properties as a strong oxidizing or bleaching agent. It also functions as a reagent in the synthesis of chemical compounds. Various grades of hydrogen peroxides have different uses: 3% and 6% solutions are used for medicinal and cosmetic purposes; the 30% solution is used for laboratory reagent purposes, the 35% and 50% solutions for most industrial applications, the 70% solution for some organic oxidation uses, and the 90% solution for some industrial uses and as a propellant for military and space programmes. Solutions of over 90% are utilized for specialized military purposes.

Hydrogen peroxide is utilized in the production of glycerin, plasticizers, bleaching agents, pharmaceuticals, cosmetics, drying agents for fats, oils and waxes, and amine oxides for home dishwashing detergents. It is used in the textile industry for bleaching textiles, particularly cotton, and in the pulp and paper industry for the bleaching of mechanical wood pulps. In mining, hydrogen peroxide is used to increase the solubility of uranium in leaching solutions. It is also useful for metal etching and oxidizing in the electronics industry and for treating metal surfaces. In addition, hydrogen peroxide is a sterilizing agent in the food industry and a source of oxygen in respiratory protective equipment.


The major hazards are fire and explosion. Organic peroxides are fuel-rich compounds that generally ignite easily and burn vigorously. The oxygen-oxygen bond is thermally unstable, decomposing exothermically at an increasing rate as temperature rises. Thermal instability varies widely. The 10-hour half-life temperatures of organic peroxides range from about 25 °C to about 172 °C. Decomposition products generally are flammable vapours which can form explosive mixtures in air; they may be hot enough to auto-ignite on contact with air if decomposition is rapid. Decomposition can be initiated by heat, friction, mechanical shock or contamination, though sensitivity to these stimuli varies greatly. If the heat of decomposition is not carried away quickly enough, a reaction ranging from mild gassing to violent spontaneous decomposition, deflagration or explosion can result. Peroxides formed spontaneously in various low-molecular-weight ethers and aldehydes are extremely sensitive to friction and impact shock. Methyl ethyl ketone peroxide and peroxyacetic acid are extremely shock sensitive, requiring diluents for safe handling. Dry benzoyl peroxide is shock sensitive. Dicumyl peroxide is insensitive to shock and friction. Shock sensitivity may be increased at elevated temperatures. Vigorous decomposition can be stimulated by even trace amounts of a wide variety of contaminants, such as strong acids, bases, metals, metal alloys and salts, sulphur compounds, amines, accelerators or reducing agents. This is particularly true of methyl ethyl ketone and benzoyl peroxides, which are intentionally stimulated to decompose at room temperature using small amounts of accelerators. The violence of decomposition is greatly affected by the quantity and type of peroxide, rate of temperature rise, amount and type of contamination, and degree of confinement.

The safety of many organic peroxides is greatly improved by dispersing them in solvent or non-solvent diluents that absorb the heat of decomposition (e.g., water or plasticizer) or reduce shock sensitivity (e.g., dimethyl phthalate). These formulations are generally much less flammable than the pure peroxide. Some are fire-resistant. However, the toxicity of the diluent may markedly increase the toxicity of the peroxide solution.

The main toxic effect of most of the peroxides is irritation of skin, mucous membranes and eyes. Prolonged or intense skin contact or splashes in the eyes may cause severe injury. Some organic peroxide vapours are irritating and may also cause headaches, intoxication similar to alcohol, and lung oedema if inhaled in high concentrations. Some, such as cumene hydroperoxides, are known skin sensitizers. Dialkyl peroxides are generally not as strongly irritating, and the diacyl peroxides are the least irritating of the peroxides. Hydroperoxides, peroxyacids and particularly methyl ethyl ketone peroxide are much more severe. They are extremely irritating and corrosive to the eyes, with risk of blindness, and may cause serious injury or death if ingested in sufficient quantity.

The carcinogenicity of the peroxides has been under investigation, but the results to date are not conclusive. The International Agency for Research on Cancer (IARC) has assigned a Group 3 rating (non-classifiable as to carcinogenicity) to benzoyl peroxide, benzoyl chloride and hydrogen peroxide

Benzoyl peroxide. The hazards of dry benzoyl peroxide are greatly reduced by dispersing it in non-solvent diluents that absorb any heat of decomposition and provide other benefits. Benzoyl peroxide is commonly produced in hydrated granular form with 20 or 30% water, and in various pastes, usually containing about 50% of a plasticizer or other diluents. These formulations have greatly reduced flammability and shock sensitivity compared to dry benzoyl peroxide. Some are fire-resistant. The hardeners used with plastic resin fillers, such as auto body putty, typically contain 50% benzoyl peroxide in a paste formulation. Flour bleach contains 32% benzoyl peroxide with 68% grain starch and calcium sulphate dihydrate or dicalcium phosphate dihydrate, and is considered non-flammable. Acne creams, also non-flammable, contain 5 or 10% benzoyl peroxide.

Hydrogen peroxide is commercially available in aqueous solutions, usually 35%, 50% (industrial strength), 70% and 90% (high strength) by weight, but also is available in 3%, 6%, 27.5% and 30% solutions. It is also sold by “volume strength” (meaning the amount of oxygen gas which will be liberated per ml of solution). Hydrogen peroxide is stabilized during manufacture to prevent contamination by metals and other impurities; however, if excessive contamination occurs, the additive cannot inhibit decomposition.

Human exposure by inhalation may result in extreme irritation and inflammation of nose, throat and respiratory tract; pulmonary oedema, headache, dizziness, nausea, vomiting, diarrhoea, irritability, insomnia, hyper-reflexia; and tremors and numbness of extremities, convulsions, unconsciousness and shock. The latter symptoms are a result of severe systemic poisoning. Exposure to mist or spray may cause stinging and tearing of the eyes. If hydrogen peroxide is splashed into the eye, severe damage such as ulceration of the cornea may result; sometimes, though rarely, this may appear as long as a week after exposure.

Skin contact with hydrogen peroxide liquid will result in temporary whitening of the skin; if the contamination is not removed, erythema and vesicle formation may occur.

Although ingestion is unlikely to occur, if it does the hydrogen peroxide will cause irritation of the upper gastrointestinal tract. Decomposition results in rapid liberation of O2, leading to distension of the oesophagus or stomach, and possibly severe damage and internal bleeding.

Decomposition continuously occurs even at a slow rate when the compound is inhibited, and thus it must be stored properly and in vented containers. High-strength hydrogen peroxide is a very high-energy material. When it decomposes to oxygen and water, large amounts of heat are liberated, leading to an increased rate of decomposition, since decomposition is accelerated by increases in temperature. This rate increases about 2.2 times per 10 °C temperature increase between 20 and 100 °C. Although pure hydrogen peroxide solutions are not usually explosive at atmospheric pressure, equilibrium vapour concentrations of hydrogen peroxide above 26 mol per cent (40 weight per cent) become explosive in a temperature range below the boiling point of the liquid.

Since the compound is such a strong oxidizer, when spilled on combustible materials it can set fire to them. Detonation can occur if the peroxide is mixed with incompatible (most) organic compounds. Solutions of less than 45% concentration expand during freezing; those greater than 65% contract. If rapid decomposition takes place near combustible materials, detonation can occur with exposures that lead to severe irritation of skin, eyes, and mucous membranes. Hydrogen peroxide solutions in concentrations greater than 8% are classified as corrosive liquids.

Hydrogen peroxide is not itself flammable but can cause spontaneous combustion of flammable materials and continued support of the combustion because it liberates oxygen as it decomposes. It is not considered to be an explosive; however, when mixed with organic chemicals, hazardous impact-sensitive compounds may result. Materials with metal catalysts can cause explosive decomposition.

Contamination of hydrogen peroxide by such metals as copper, cobalt, manganese, chromium, nickel, iron and lead, and their salts, or by dust, dirt, oils, various enzymes, rust and undistilled water results in an increased rate of decomposition. Decomposition results in the liberation of oxygen and heat. If the solution is dilute, the heat is readily absorbed by the water present. In more concentrated solutions the heat increases the temperature of the solution and its decomposition rate. This may lead to an explosion. Contamination with materials containing metal catalysts can result in immediate decomposition and explosive rupture of the container if it is not properly vented. When an ammonium peroxidisulphate route is used in the production of hydrogen peroxide, a risk of bronchial and skin sensitization may be present.

Safety Precautions

Spills should be cleaned up promptly using non-sparking tools and an inert, moist diluent such as vermiculite or sand. Sweepings may be placed in open containers or polyethylene bags and the area washed with water and detergent. Spilled, contaminated, waste or questionable peroxides should be destroyed. Most peroxides can be hydrolyzed by adding them slowly with stirring to about ten times their weight of cold 10% sodium hydroxide solution. The reaction may require several hours. Rigid containers of uncertain age or condition should not be opened but carefully burned from a safe distance.

Persons handling peroxides should use safety glasses with side shields, goggles or face shields for eye protection. Emergency eyewash facilities should be provided. Gloves, aprons and other protective clothing as necessary should be used to prevent skin contact. Clothing and equipment that generate static electricity should be avoided. Smoking should be prohibited. Peroxides should not be stored in refrigerators containing food or drink. Laboratory reactions should be carried out behind a safety shield.

Storage and handling areas should be protected from fire by a deluge system or sprinklers. (A liquid nitrogen deluge system may be used for protection of peroxides which are stable only below the freezing point of water.) In case of fire, water should be applied by the sprinkler system or by hose from a safe distance, preferably with a fog nozzle. Foam may be necessary instead if the peroxide is diluted in a low density flammable solvent. Portable extinguishers should not be used except for very small fires. Peroxides threatened by fire should be wetted from a safe distance for cooling.

Peroxides should be washed promptly from the skin to prevent irritation. In the case of eye contact, the eyes should be flushed immediately with large amounts of water, and medical attention should be obtained. Delay in the case of corrosive irritants such as methyl ethyl ketone peroxide can result in blindness. Medical attention should also be obtained in case of accidental ingestion. If sensitization occurs, further contact should be avoided.

Organic and inorganic peroxides tables

Table 1 - Chemical information.

Table 2 - Health hazards.

Table 3 - Physical and chemical hazards.

Table 4 - Physical and chemical properties.



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