In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...
, organic peroxides are
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s containing the
peroxide
In chemistry, peroxides are a group of compounds with the structure , where R = any element. The group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable.
The most common peroxide is hydrogen ...
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the res ...
(). If the R′ is
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
, the compounds are called
hydroperoxides, which are discussed in that article. The O−O bond of peroxides easily breaks, producing
free radical
A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing.
Ageing
Ailments of unknown cause
Biogerontology
Biological processes
Causes of death
Cellular processes
Gerontology
Life extension
Metabo ...
s of the form (the dot represents an
unpaired electron). Thus, organic peroxides are useful as
initiators for some types of
polymerisation, such as the
epoxy
Epoxy is the family of basic components or Curing (chemistry), cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional ...
resin
In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on n ...
s used in
glass-reinforced plastic
Fiberglass (American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cloth ...
s.
MEKP and
benzoyl peroxide
Benzoyl peroxide is a chemical compound (specifically, an organic peroxide) with structural formula , often abbreviated as (BzO)2. In terms of its structure, the molecule can be described as two benzoyl (, Bz) groups connected by a 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
Bleach is the generic name for any chemical product that is used industrially or domestically to remove color (whitening) from a fabric or fiber or to clean or to remove stains in a process called bleaching. It often refers specifically, to ...
agents.
Types of organic peroxides
Tert-Butyl hydroperoxide Structural Formula V2.svg, ''tert''-Butyl hydroperoxide, a hydroperoxide (formula: ROOH) that is used to epoxide alkenes.
Dicumyl peroxide.svg, Dicumyl peroxide
Dicumyl peroxide is an organic compound with the formula (Me = CH3). Classified as a dialky peroxide, it is produced on a large scale industrially for use as an initiator for the production of low density polyethylene.
Production
It is synth ...
, a dialkyl peroxide (formula: ROOR) that is used to initiate polymerizations.
Tert-Butylperoxybenzoat Strukturformel.svg, ''tert''-butylperoxybenzoate, a peroxy ester (formula: ) that used as a radical initiator.
Benzoyl-peroxide.svg, dibenzoyl peroxide, a diacyl peroxide (formula: ) is also used as an initiator for polymerizations.
Ethaneperoxoic acid 200.svg, Peroxyacetic acid, a peroxycarboxylic acid (formula: ), is a reagent in organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
.
Organic peroxides are classified (i) by the presence or absence of a hydroxyl (-OH) terminus and (ii) by the presence of alkyl vs acyl substituents. 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.
Properties
The O−O
bond length
In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest ...
in peroxides is about 1.45
Å, and the R−O−O angles (R = H, C) are about 110° (water-like). Characteristically, the C−O−O−R (R = H, C) dihedral angles are about 120°. The O−O bond is relatively weak, with a
bond dissociation energy
The bond-dissociation energy (BDE, ''D''0, or ''DH°'') is one measure of the strength of a chemical bond . It can be defined as the standard enthalpy change when is cleaved by homolysis to give fragments A and B, which are usually radical ...
of , less than half the strengths of C−C, C−H, and C−O bonds.
Biology
Peroxides play important roles in biology. Many aspects of biodegradation or aging are attributed to the formation and decay of peroxides formed from oxygen in air. Countering these effects is an array of biological and artificial
antioxidant
Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricants ...
s.
Hundreds of peroxides and hydroperoxides are known, being derived from fatty acids, steroids, and terpenes. Fatty acids form a number of 1,2-dioxenes. The biosynthesis
prostaglandin
The prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are der ...
s proceeds via an endoperoxide, a class of bicyclic peroxides.
In
fireflies, oxidation of
luciferins, which is catalyzed by
luciferase
Luciferase is a generic term for the class of oxidative enzymes that produce bioluminescence, and is usually distinguished from a photoprotein. The name was first used by Raphaël Dubois who invented the words '' luciferin'' and ''luciferase'' ...
s, yields a peroxy compound
1,2-dioxetane. The dioxetane is unstable and decays spontaneously to
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
and excited
ketone
In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bon ...
s, which release excess energy by emitting light (
bioluminescence
Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some ...
).
Industrial uses
In polymer chemistry
Many peroxides are used as a
radical initiators, e.g., to enable
polymerization
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...
of acrylates. Industrial resins based on acrylic and/or
methacrylic acid
Methacrylic acid, abbreviated MAA, is an organic compound. This colorless, viscous liquid is a carboxylic acid with an acrid unpleasant odor. It is soluble in warm water and miscible with most organic solvents. Methacrylic acid is produced indus ...
esters are invariably produced by radical polymerization with organic peroxides at elevated temperatures. The polymerization rate is adjusted by suitable choice of temperature and type of peroxide.
Methyl ethyl ketone peroxide,
benzoyl peroxide
Benzoyl peroxide is a chemical compound (specifically, an organic peroxide) with structural formula , often abbreviated as (BzO)2. In terms of its structure, the molecule can be described as two benzoyl (, Bz) groups connected by a peroxide () ...
and to a smaller degree
acetone peroxide are used as initiators for
radical polymerisation
In polymer chemistry, free-radical polymerization (FRP) is a method of polymerization by which a polymer forms by the successive addition of free-radical building blocks (repeat units). Free radicals can be formed by a number of different mechanis ...
of some
resin
In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on n ...
s, e.g.
polyester and
silicone, often encountered when making
fiberglass
Fiberglass (American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cl ...
.
Pinane hydroperoxide
Pinane is a set of isomeric terpenes. Existing as chiral cis and trans isomers, they arise from the hydrogenation of pinene. Both isomers undergo reaction with air to give 2-pinane hydroperoxides, also with chiral cis and trans isomers. Partial ...
is used in production of
styrene-butadiene
Styrene-butadiene or styrene-butadiene rubber (SBR) describe families of synthetic rubbers derived from styrene and butadiene (the version developed by Goodyear is called Neolite). These materials have good abrasion resistance and good aging st ...
(
synthetic rubber
A synthetic rubber is an artificial elastomer. They are polymers synthesized from petroleum byproducts. About 32-million metric tons of rubbers are produced annually in the United States, and of that amount two thirds are synthetic. Synthetic rubbe ...
).
Bleaching and disinfecting agents
Benzoyl peroxide
Benzoyl peroxide is a chemical compound (specifically, an organic peroxide) with structural formula , often abbreviated as (BzO)2. In terms of its structure, the molecule can be described as two benzoyl (, Bz) groups connected by a peroxide () ...
and
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3% ...
are used as
bleaching and "maturing" agents for treating
flour
Flour is a powder made by grinding raw grains, roots, beans, nuts, or seeds. Flours are used to make many different foods. Cereal flour, particularly wheat flour, is the main ingredient of bread, which is a staple food for many c ...
to make its grain release
gluten
Gluten is a structural protein naturally found in certain cereal grains. Although "gluten" often only refers to wheat proteins, in medical literature it refers to the combination of prolamin and glutelin proteins naturally occurring in all gra ...
more easily; the alternative is letting the flour slowly oxidize by air, which is too slow for the industrialized era.
Benzoyl peroxide
Benzoyl peroxide is a chemical compound (specifically, an organic peroxide) with structural formula , often abbreviated as (BzO)2. In terms of its structure, the molecule can be described as two benzoyl (, Bz) groups connected by a peroxide () ...
is an effective topical medication for treating most forms of
acne
Acne, also known as ''acne vulgaris'', is a long-term skin condition that occurs when dead skin cells and oil from the skin clog hair follicles. Typical features of the condition include blackheads or whiteheads, pimples, oily skin, and ...
.
Preparation
Dialkyl peroxides, e.g.,
dicumyl peroxide
Dicumyl peroxide is an organic compound with the formula (Me = CH3). Classified as a dialky peroxide, it is produced on a large scale industrially for use as an initiator for the production of low density polyethylene.
Production
It is synth ...
, are synthesized by addition of hydrogen peroxide to alkenes or by O-alkylation of hydroperoxides.
Diacyl peroxides are typically prepared by treating hydrogen peroxide with acid chlorides or acid anhydrides in the presence of base:
[
:
:
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.
]Perester
In organic chemistry, organic peroxides are organic compounds containing the peroxide functional group (). If the R′ is hydrogen, the compounds are called hydroperoxides, which are discussed in that article. The O−O bond of peroxides easily b ...
s, an example being ''tert''-Butyl peroxybenzoate, are produced by treating acid anhydrides or acid chlorides with hydroperoxides.
This method can also yield cyclic peroxides. The four-membered dioxetane
A dioxetane or dioxacyclobutane is an organic compound with formula C2O2H4, whose backbone is a four-membered ring of two oxygen atoms and two carbon atoms. There are two isomers:
* 1,2-dioxetane where the oxygen atoms are adjacent.
* 1,3-dioxetan ...
s can be obtained by 2+2 cycloaddition
In organic chemistry, a cycloaddition is a chemical reaction in which "two or more unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity". ...
of oxygen to alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s.
Reactions
Homolysis
Organic peroxides are widely used to initiate polymerization
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...
of olefin
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s, e.g. the formation of polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including ...
. A key step is homolysis:
:.
The tendency to homolyze is also exploited to modify polymers by grafting
Grafting or graftage is a horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion () while the lower part is called the rootstock. The succ ...
or visbreaking, or cross-link
In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...
polymers to create a thermoset
In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and ...
. When used for these purposes, the peroxide is highly diluted, so the heat generated by the exothermic
In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity ...
decomposition is safely absorbed by the surrounding medium (e.g. polymer compound or emulsion
An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Althou ...
).
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 rate
Rate or rates may refer to:
Finance
* Rates (tax), a type of taxation system in the United Kingdom used to fund local government
* Exchange rate, rate at which one currency will be exchanged for another
Mathematics and science
* Rate (mathema ...
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).
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):
:
Reduction
Organoperoxides can be reduced to alcohol
Alcohol most commonly refers to:
* Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom
* Alcohol (drug), an intoxicant found in alcoholic drinks
Alcohol may also refer to:
Chemicals
* Ethanol, one of sev ...
s with lithium aluminium hydride
Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula Li Al H4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic ...
, as described in this idealized equation:
:
The phosphite esters and tertiary phosphines also effect reduction:
:
Cleavage to ketones and alcohols in the base catalyzed Kornblum–DeLaMare rearrangement
Some peroxides are drug
A drug is any chemical substance that causes a change in an organism's physiology or psychology when consumed. Drugs are typically distinguished from food and substances that provide nutritional support. Consumption of drugs can be via inhal ...
s, whose action is based on the formation of radicals at desired locations in the organism. For example, artemisinin
Artemisinin () and its semisynthetic derivatives are a group of drugs used in the treatment of malaria due to '' Plasmodium falciparum''. It was discovered in 1972 by Tu Youyou, who shared the 2015 Nobel Prize in Physiology or Medicine for her ...
and its derivatives, such as artesunate
Artesunate (AS) is a medication used to treat malaria. The intravenous form is preferred to quinine for severe malaria. Often it is used as part of combination therapy, such as artesunate plus mefloquine. It is not used for the prevention of mal ...
, possess the most rapid action of all current drugs against falciparum
''Plasmodium falciparum'' is a unicellular protozoan parasite of humans, and the deadliest species of '' Plasmodium'' that causes malaria in humans. The parasite is transmitted through the bite of a female '' Anopheles'' mosquito and causes ...
malaria
Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or deat ...
. Artesunate is also efficient in reducing egg production in '' Schistosoma haematobium'' infection.
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-starch reaction. Here peroxides, hydroperoxides or peracids oxidize the added potassium iodide
Potassium iodide is a chemical compound, medication, and dietary supplement. It is a medication used for treating hyperthyroidism, in radiation emergencies, and for protecting the thyroid gland when certain types of radiopharmaceuticals are us ...
into iodine
Iodine is a chemical element with the Symbol (chemistry), symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , ...
, which reacts with starch
Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...
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 indigo dye
Indigo dye is an organic compound with a distinctive blue color. Historically, indigo was a natural dye extracted from the leaves of some plants of the ''Indigofera'' genus, in particular '' Indigofera tinctoria''; dye-bearing ''Indigofera'' p ...
s in presence of peroxides is used instead for this purpose. For example, the loss of blue color in leuco-methylene blue
Methylthioninium chloride, commonly called methylene blue, is a salt used as a dye and as a medication. Methylene blue is a thiazine dye. As a medication, it is mainly used to treat methemoglobinemia by converting the ferric iron in hemoglob ...
is selective for hydrogen peroxide.
Quantitative analysis of hydroperoxides can be performed using potentiometric titration
Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the ''titrant ...
with lithium aluminium hydride
Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula Li Al H4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic ...
. Another way to evaluate the content of peracids and peroxides is the volumetric titration with alkoxides such as sodium ethoxide.
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
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number 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
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
of the organic groups, the lower the energy content and, usually, the lower the hazard.
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
The molecular mass (''m'') is the mass of a given molecule: it is measured in daltons (Da or u). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The related quant ...
of the pure peroxide.
Organic peroxides are often sold as formulations that include one or more phlegmatizing agents. 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.
Safety
Peroxides are also strong oxidizers and easily react with skin, cotton and wood pulp. For safety reasons, peroxidic compounds are stored in a cool, opaque container, as heating and illumination accelerate their chemical reaction
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and break ...
s. Small amounts of peroxides, which emerge from storage or reaction vessels are neutralized using reducing agents such as iron(II) sulfate
Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula Fe SO4·''x''H2O. These compounds exist most commonly as the hepta hydrate (''x'' = 7) but several values for x are kno ...
. Safety measures in industrial plants producing large amounts of peroxides include the following:
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
/ref>
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
The self-accelerating decomposition temperature (SADT) is the lowest temperature at which an organic peroxide in a typical vessel or shipping package will undergo a self-accelerating decomposition within one week. The SADT is the point at which th ...
of the compound.
The shipping of organic peroxides is restricted. The US Department of Transportation
The United States Department of Transportation (USDOT or DOT) is one of the executive departments of the U.S. federal government. It is headed by the secretary of transportation, who reports directly to the President of the United States an ...
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:
See also
* Alkenyl peroxides
In organic chemistry, alkenyl peroxides are organic compoundss bearing an alkene () residue directly at the peroxide () group, resulting in the general formula . They have very weak O-O bonds and are thus generally unstable compounds.
Propertie ...
* Peroxyacyl nitrates
* Ozonide
Ozonide is the polyatomic anion . Cyclic organic compounds formed by the addition of ozone () to an alkene are also called ozonides.
Ionic ozonides
Inorganic ozonides are dark red salts. The anion has the bent shape of the ozone molecule.
In ...
External links
Organic Peroxide Producers Safety Division
*
European Organic Peroxide Safety Group
References
{{Functional group
Organic compounds
Food additives
Functional groups