Alkenyl Peroxides on:
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The significant weakness of the O-O bond can be explained by formation of the resonance stabilized alkenyloxyl radical and the strong carbonyl bond, respectively. This reasoning also applies to aryl peroxides. Both compound classes thus have significantly weaker O-O bonds than other peroxides. Because of this weak bond, alkenyl peroxides are generally only postulated as reactive intermediates. An exception is the case of some few heteroarylperoxides, which were long-lived enough to be characterized.
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 matter, organic materials, i.e., matter in its various forms that contain ...
, alkenyl peroxides are organic peroxides
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 ...
bearing an alkene
In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins.
The Internationa ...
() residue directly at the peroxide
In chemistry, peroxides are a group of Chemical compound, compounds with the structure , where the R's represent a radical (a portion of a complete molecule; not necessarily a free radical) and O's are single oxygen atoms. Oxygen atoms are joined ...
() group, resulting in the general formula . They have very weak O-O bonds and are thus generally unstable compounds.
Properties
Alkenyl peroxides decompose readily by homolytic O-O bond cleavage into tworadicals
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, generating an oxyl radical and an alkenyloxyl- or α-oxo-alkyl radical.
The significant weakness of the O-O bond can be explained by formation of the resonance stabilized alkenyloxyl radical and the strong carbonyl bond, respectively. This reasoning also applies to aryl peroxides. Both compound classes thus have significantly weaker O-O bonds than other peroxides. Because of this weak bond, alkenyl peroxides are generally only postulated as reactive intermediates. An exception is the case of some few heteroarylperoxides, which were long-lived enough to be characterized.
Occurrence
In the atmosphere
Alkenyl hydroperoxides (R1 = H) have been postulated as reactive intermediates inatmospheric chemistry
Atmospheric chemistry is a branch of atmospheric science that studies the chemistry of the Earth's atmosphere and that of other planets. This multidisciplinary approach of research draws on environmental chemistry, physics, meteorology, comput ...
.. They are formed via ozonolysis
In organic chemistry, ozonolysis is an organic reaction where the Saturated and unsaturated compounds, unsaturated bonds are Bond cleavage, cleaved with ozone (). Multiple carbon–carbon bond are replaced by carbonyl () groups, such as aldehydes ...
of alkene
In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins.
The Internationa ...
s in the atmosphere
An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
and form hydroxyl radical
The hydroxyl radical, •HO, is the neutral form of the hydroxide ion (HO–). Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry. Most notably hydroxyl radicals are pr ...
s upon decay, which play an important role in the decomposition of pollutants in the air. During day-time, hydroxyl radicals form predominantly photochemically
Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible (400–750&nb ...
by irradiation with light; whereas in the dark during night-time, the formation via alkenyl peroxides is believed to be their major source.
In solution
Alkenyl peroxides can be formed by acid catalyzedcondensation
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor ...
of ketone
In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...
s with organic hydroperoxides or 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 viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...
. This has been suggested based on the characterization of the corresponding products of decomposition. Alkenyl peroxides could also occur as unwanted byproducts in the Baeyer–Villiger oxidation
The Baeyer–Villiger oxidation is an organic reaction that forms an ester from a ketone or a lactone from a cyclic ketone, using peroxyacids or peroxides as the oxidant. The reaction is named after Adolf von Baeyer and Victor Villiger who first ...
when using hydrogen peroxide, which would diminish the effectiveness of this reaction.
Applications
The radicals formed from alkenyl peroxides can be utilized in organic radical reactions. For example, they can mediatehydrogen atom abstraction
In chemistry, hydrogen atom abstraction, or hydrogen atom transfer (HAT), refers to a class of chemical reactions where a hydrogen free radical (a neutral hydrogen atom) is removed from a substrate with another molecule. This process follows the g ...
reactions and thus lead to the functionalization of C-H bonds, or they can be used to introduce ketone residues by addition of the alkenyloxyl radicals to alkenes.{{cite journal, doi=10.1016/j.tet.2015.06.106 , title=Acid-catalyzed cascade radical addition/Cyclization of arylacrylamides with ketones , date=2015 , last1=Xia , first1=Xiao-Feng , last2=Zhu , first2=Su-Li , last3=Zeng , first3=Minglu , last4=Gu , first4=Zhen , last5=Wang , first5=Haijun , last6=Li , first6=Wei , journal=Tetrahedron , volume=71 , issue=36 , pages=6099–6103 .
References