Alkenyl Peroxides on:
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The significant weakness of the O-O bond can be explained by formation of the
In organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the 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.Clayden, J.; ...
, alkenyl peroxides are organic compounds
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. The s ...
s bearing an 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 ...
() residue directly at 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 p ...
() 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 two radicals, 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
In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or ...
alkenyloxyl radical and the strong carbonyl bond, respectively.N. Sebbar, J. W. Bozzelli, H. Bockhorn, ''J. Phys. Chem. A'' 2004, 108, 8353–8366. This reasoning also applies to aryl peroxides. Both compound classes thus have significantly weaker O-O bonds than other peroxides.B. Schweitzer-Chaput, T. Kurtén, M. Klussmann, ''Angew. Chem. Int. Ed.'' 2015, 54, 11848–11851. 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 in which the chemistry of the Earth's atmosphere and that of other planets is studied. It is a multidisciplinary approach of research and draws on environmental chemistry, physics, meteoro ...
.R. Atkinson, J. Arey, ''Atmospheric Environment'' 2003, 37, Supplement 2, 197-219. They are formed via ozonolysis
In organic chemistry, ozonolysis is an organic reaction where the unsaturated bonds of alkenes (), alkynes (), or azo compounds () are cleaved with ozone (). Alkenes and alkynes form organic compounds in which the multiple carbon–carbon bond ...
of 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 in the atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
and form hydroxyl radical
The hydroxyl radical is the diatomic molecule . The hydroxyl radical is very stable as a dilute gas, but it decays very rapidly in the condensed phase. It is pervasive in some situations. Most notably the hydroxyl radicals are produced from the ...
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 light (400–7 ...
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 to ...
of 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 bo ...
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 viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%†...
. 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 fir ...
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, a hydrogen atom abstraction or hydrogen atom transfer (HAT) is any chemical reaction in which a hydrogen free radical (neutral hydrogen atom) is abstracted from a substrate according to the general equation:
:X^\bullet + H-Y -> X-H ...
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.X.-F. Xia, S.-L. Zhu, M. Zeng, Z. Gu, H. Wang, W. Li, ''Tetrahedron'' 2015, 71, 6099–6103, {{doi, 10.1016/j.tet.2015.06.106.
References