Schenck Ene Reaction on:
[Wikipedia]
[Google]
[Amazon]
The Schenck ene reaction or the Schenk reaction is the reaction of 
Experimental and computational studies show that the reaction actually proceeds via a two step no intermediate process. One can loosely interpret it as a mix of the perepoxide mechanism and the concerted mechanism. There is no perepoxide intermediate as in the classical sense of 
Very bulky groups, like the
Many hydroperoxides derived from fatty acids, steroids, and terpenes are also formed via the Schenck ene reaction. For instance, the generation of 
It must be noted, however, that this
singlet oxygen
Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemistry, inorganic chemical with the formula O=O (also written as or ), which is in a quantum state where all electrons are Radical (chemistry), spin p ...
with alkenes
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 ...
to yield hydroperoxides
Hydroperoxides or peroxols are compounds of the form ROOH, where R stands for any group, typically organic, which contain the hydroperoxy functional group (). Hydroperoxide also refers to the hydroperoxide anion () and its salts, and the neutra ...
. The hydroperoxides can be reduced to allylic
In organic chemistry, an allyl group is a substituent with the structural formula . It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, . In 1844, Theodor Wertheim isolat ...
alcohols
In chemistry, an alcohol (), is a type of organic compound that carries at least one hydroxyl () functional group bound to a Saturated and unsaturated compounds, saturated carbon atom. Alcohols range from the simple, like methanol and ethanol ...
or eliminate to form unsaturated carbonyl compounds. It is a type II photooxygenation reaction, and is discovered in 1944 by Günther Otto Schenck. Its results are similar to ene reactions, hence its name.
Reaction conditions
The singlet oxygen reagent can be produced via photochemical activation oftriplet oxygen
Triplet oxygen, 3O2, refers to the ''S'' = 1 electronic ground state of molecular oxygen (dioxygen). Molecules of triplet oxygen contain two unpaired electrons, making triplet oxygen an unusual example of a stable and commonly encountered diradi ...
(regular oxygen) in the presence of photosensitizers like rose bengal
Rose bengal (4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein) is a staining (biology), stain. Rose bengal belongs to the class of organic compounds called xanthenes. Its sodium salt is commonly used in eye drops to stain damaged conjuncti ...
. Chemical processes like the reaction between 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 ...
and sodium hypochlorite
Sodium hypochlorite is an alkaline inorganic chemical compound with the formula (also written as NaClO). It is commonly known in a dilute aqueous solution as bleach or chlorine bleach. It is the sodium salt of hypochlorous acid, consisting of ...
are also viable.
Mechanism and selectivity
Historically, four mechanisms have been proposed:Experimental and computational studies show that the reaction actually proceeds via a two step no intermediate process. One can loosely interpret it as a mix of the perepoxide mechanism and the concerted mechanism. There is no perepoxide intermediate as in the classical sense of reaction intermediates
In chemistry, a reaction intermediate, or intermediate, is a molecular entity arising within the sequence of a stepwise chemical reaction. It is formed as the reaction product of an elementary step, from the reactants and/or preceding intermed ...
, for there exists no energy barrier
In the Arrhenius model of reaction rates, activation energy is the minimum amount of energy that must be available to reactants for a chemical reaction to occur. The activation energy (''E''a) of a reaction is measured in kilojoules per mole (k ...
between it and the hydroperoxide product.
Such a mechanism can account for the selectivity of the Schenck ene reaction. The singlet oxygen is more likely to abstract hydrogen from the side with more C-H bonds due to favorable interactions in the transition state:
Very bulky groups, like the tertiary
Tertiary (from Latin, meaning 'third' or 'of the third degree/order..') may refer to:
* Tertiary period, an obsolete geologic period spanning from 66 to 2.6 million years ago
* Tertiary (chemistry), a term describing bonding patterns in organic ch ...
butyl
In organic chemistry, butyl is a four-carbon alkyl radical or substituent group with general chemical formula , derived from either of the two isomers (''n''-butane and isobutane) of butane.
The isomer ''n''-butane can connect in two ways, giv ...
group, will hinder hydrogen abstraction on that side.
Applications
The Schenck ene reaction is utilized in thebiological
Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, origin, evolution, and distribution of ...
and biomimetic
Biomimetics or biomimicry is the emulation of the models, systems, and elements of nature for the purpose of solving complex human problems. The terms "biomimetics" and "biomimicry" are derived from (''bios''), life, and μίμησις ('' mīm ...
synthesis of rhodonoids, yield
Many hydroperoxides derived from fatty acids, steroids, and terpenes are also formed via the Schenck ene reaction. For instance, the generation of cis-3-hexenal
''cis''-3-Hexenal, also known as (''Z'')-3-hexenal and leaf aldehyde, is an organic compound with the formula CH3CH2CH=CHCH2CHO. It is classified as an unsaturated aldehyde. It is a colorless liquid and an aroma compound with an intense odor of ...
from linolenic acid
Linolenic acid is a type of naturally-occurring fatty acid. It can refer to either of two octadecatrienoic acids (i.e. with an 18-carbon chain and three double bonds, which are found in the '' cis'' configuration), or a mixture of the two. Lino ...
:
It must be noted, however, that this enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
catalyzed path follows a different mechanism from the usual Schenck ene reaction. Radicals are involved, and triplet oxygen
Triplet oxygen, 3O2, refers to the ''S'' = 1 electronic ground state of molecular oxygen (dioxygen). Molecules of triplet oxygen contain two unpaired electrons, making triplet oxygen an unusual example of a stable and commonly encountered diradi ...
is used instead of singlet oxygen.
See also
*Ene reaction
In organic chemistry, the ene reaction (also known as the Alder-ene reaction by its discoverer Kurt Alder in 1943) is a chemical reaction between an alkene with an allylic hydrogen (the ene) and a compound containing a multiple bond (the enophile) ...
* Photooxygenation
* Singlet oxygen
Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemistry, inorganic chemical with the formula O=O (also written as or ), which is in a quantum state where all electrons are Radical (chemistry), spin p ...
* Hydroperoxide
Hydroperoxides or peroxols are Chemical compound, compounds of the form ROOH, where R stands for any group, typically Organic compound, organic, which contain the hydroperoxy functional group (). Hydroperoxide also refers to the hydroperoxide anio ...
References
{{reflist Organic reactions Reaction mechanisms