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In organic chemistry, organic peroxides are containing the peroxide functional group (). If the R′ is hydrogen, the compounds are called , which are discussed in that article. The O−O bond of peroxides easily breaks, producing of the form (the dot represents an unpaired electron). Thus, organic peroxides are useful as initiators for some types of polymerization, such as the Acrylic resin, unsaturated polyester, and vinyl ester used in glass-reinforced plastics. MEKP and benzoyl peroxide are commonly used for this purpose. However, the same property also means that organic peroxides can explosively combust. Organic peroxides, like their inorganic counterparts, are often powerful bleaching agents.
One gap in the classes of organic peroxides is diphenyl peroxide. Quantum chemical calculations predict that it undergoes a nearly barrierless reaction akin to the benzidine rearrangement.
Many aspects of biodegradation or aging are attributed to the formation and decay of peroxides formed from oxygen in air. Countering these effects, an array of biological and artificial destroy peroxides.
In firefly, oxidation of luciferins, which is catalyzed by , yields a peroxy compound 1,2-dioxetane. The dioxetane is unstable and decays spontaneously to carbon dioxide and excited , which release excess energy by emitting light (bioluminescence).Aldo Roda Chemiluminescence and Bioluminescence: Past, Present and Future, p. 57, Royal Society of Chemistry, 2010,
Methyl ethyl ketone peroxide, benzoyl peroxide and to a smaller degree acetone peroxide are used as initiators for radical polymerization of some , e.g. unsaturated polyester and vinyl ester resins, often encountered when making fiberglass or carbon fiber composites (CFRP), with examples including boats, RV units, bath tubs, pools, sporting equipment, wind turbine blades, and a variety of industrial applications.
Benzoyl peroxide, /, and alkylperoxy monocarbonates are used in production of polystyrene, expanded polystyrene, and High Impact Polystyrene, and benzoyl peroxide is utilized for many acrylate based adhesive applications.
Thermoplastic production techniques for many industrial polymerization applications include processes which are carried out in bulk, solution, or suspension type batches. Relevant polymers include: polyvinyl chloride (PVC), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polymethyl methacrylate (PMMA), Polystyrene, and Polycarbonates.
Diacyl peroxides are typically prepared by treating hydrogen peroxide with acid chlorides or acid anhydrides in the presence of base:
, an example being tert-Butyl peroxybenzoate, are produced by treating acid anhydrides or acid chlorides with hydroperoxides.
The hazards associated with storage of ethers in air is attributed to the formation of hydroperoxides via the direct albeit slow reaction of triplet oxygen with .
The tendency to homolyze is also exploited to modify polymers by graft polymer or visbreaker, or cross-link polymers to create a thermoset. When used for these purposes, the peroxide is highly diluted, so the heat generated by the exothermic decomposition is safely absorbed by the surrounding medium (e.g. polymer compound or emulsion).
The and tertiary phosphines also effect reduction:
Cleavage to ketones and alcohols occurs in the base-catalyzed Kornblum–DeLaMare rearrangement, which involves the breaking of bonds within peroxides to form these products.
Some peroxides are , whose action is based on the formation of radicals at desired locations in the organism. For example, artemisinin and its derivatives, such as artesunate, possess the most rapid action of all current drugs against falciparum malaria. Artesunate is also efficient in reducing egg production in Schistosoma haematobium infection.
Quantitative analysis of hydroperoxides can be performed using potentiometric titration with lithium aluminium hydride. Another way to evaluate the content of peracids and peroxides is the volumetric titration with such as sodium ethoxide.
The term active oxygen is used to specify the amount of peroxide present in any organic peroxide formulation. One of the oxygen atoms in each peroxide group is considered "active". The theoretical amount of active oxygen can be described by the following equation:
where is the number of peroxide groups in the molecule, and is the molecular mass of the pure peroxide.
Organic peroxides are often sold as formulations that include one or more phlegmatized. That is, for safety sake or performance benefits the properties of an organic peroxide formulation are commonly modified by the use of additives to phlegmatize (desensitize), stabilize, or otherwise enhance the organic peroxide for commercial use. Commercial formulations occasionally consist of mixtures of organic peroxides, which may or may not be phlegmatized.
1) The equipment is located within reinforced concrete structures with foil windows, which would relieve pressure and not shatter in case of explosion.
2) The products are bottled in small containers and are moved to a cold place promptly after the synthesis.
3) The containers are made of non-reactive materials such as stainless steel, some aluminium alloys or dark glass. Ozonelab Peroxide compatibility
For safe handling of concentrated organic peroxides, an important parameter is temperature of the sample, which should be maintained below the self accelerating decomposition temperature of the compound.
The shipping of organic peroxides is restricted. The US Department of Transportation lists organic peroxide shipping restrictions and forbidden materials in 49 CFR 172.101 Hazardous Materials Table based on the concentration and physical state of the material:
The reaction competes with hydrolysis of the acylating agent but the hydroperoxide anion is a superior nucleophile relative to hydroxide. Unsymmetrical diacyl peroxides can be produced by treating acyl chlorides with the peroxy acid.
From O2
Cyclic peroxides can be obtained by cycloaddition of singlet oxygen (generated by UV radiation) to dienes. An important example is rubrene. Six-membered cyclic peroxides are called endo peroxides. The four-membered dioxetanes can be obtained by 2+2 cycloaddition of oxygen to .Heinz G. O. Becker Organikum, Wiley-VCH, 2001, , p. 323
Reactions
Homolysis
Organic peroxides are widely used to initiate polymerization of , e.g. the formation of polyethylene. A key step is homolysis:
Self-oxidation
Especially when in concentrated form, organic peroxides can decompose by self-oxidation, since organic peroxides contain both an oxidizer (the O-O bond) and fuel (C-H and C-C bonds). A "self-accelerating decomposition" occurs when the reaction rate of peroxide decomposition generates heat at a faster rate than it can be dissipated to the environment. Temperature is the main factor in the rate of decomposition. The lowest temperature at which a packaged organic peroxide will undergo a self-accelerating decomposition within a week is defined as the self-accelerating decomposition temperature (SADT). A large fire at the Arkema Chemical Plant in Crosby, Texas (USA) in 2017 was caused by the decomposition of various organic peroxides following power failure and subsequent loss of cooling systems. This occurred due to extreme flooding from Hurricane Harvey, which destroyed main and back-up power generators at the site.
Cumene process
Hydroperoxides are intermediates or reagents in major commercial processes. In the cumene process, acetone and phenol are produced by decomposition of cumene hydroperoxide (Me = methyl):
Anthraquinone process
Anthrahydroquinone reacts spontaneously with oxygen to form anthraquinone and hydrogen peroxide, possibly through some organic peroxide intermediate. After extracting the hydrogen peroxide the anthraquinone is catalytically reduced to anthrahydroquinone and reused in the process. There are other reacting in a similar fashion.
Reduction
Organoperoxides can be reduced to alcohols with lithium aluminium hydride, as described in this idealized equation:
Organic synthesis
tert-Butyl hydroperoxide is used for epoxidation and hydroxylation reagents in conjunction with metal catalysts.
Analysis of peroxides
Several analytical methods are used for qualitative and quantitative determination of peroxides. A simple qualitative detection of peroxides is carried out with the iodine test. Here peroxides, hydroperoxides or peracids oxidize the added potassium iodide into iodine, which reacts with starch producing a deep-blue color. Commercial paper indicators using this reaction are available. This method is also suitable for quantitative evaluation, but it can not distinguish between different types of peroxide compounds. Discoloration of various in presence of peroxides is used instead for this purpose.Veibel, S. Analytik organischer Verbindungen, Akademie-Verlag, Berlin, 1960, p. 262 For example, the loss of blue color in leuco-methylene blue is selective for hydrogen peroxide.
Active oxygen in peroxides
Each peroxy group is considered to contain one active oxygen atom. The concept of active oxygen content is useful for comparing the relative concentration of peroxy groups in formulations, which is related to the energy content. In general, energy content increases with active oxygen content, and thus the higher the molecular weight of the organic groups, the lower the energy content and, usually, the lower the hazard.
Safety
Peroxides are also strong oxidizers and easily react with skin, cotton and wood pulp.Heinz G. O. Becker Organikum, Wiley-VCH, 2001, pp. 741–762 For safety reasons, peroxidic compounds are stored in a cool, opaque container, as heating and illumination accelerate their chemical reactions. Small amounts of peroxides, which emerge from storage or reaction vessels are neutralized using reducing agents such as iron(II) sulfate. Safety measures in industrial plants producing large amounts of peroxides include the following:
Acetyl acetone peroxide 37187-22-7 > 9% by mass active oxygen Acetyl benzoyl peroxide 644-31-5 solid, or > 40% in solution Ascaridole 512-85-6 (organic peroxide) tert-Butyl hydroperoxide 75-91-2 > 90% in solution (aqueous) Di-(1-naphthoyl)peroxide 29903-04-6 Diacetyl peroxide 110-22-5 solid, or > 25% in solution Ethyl hydroperoxide 3031-74-1 Methyl ethyl ketone peroxide 1338-23-4 > 9% by mass active oxygen in solution Methyl isobutyl ketone peroxide 37206-20-5 > 9% by mass active oxygen in solution
See also
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