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Sulfoxidation
n a phase-II detoxification pathway that occurs in the liver and in which sulfite oxidase converts
sulfites, such as those found in food preservatives and colorings, garlic compounds, and
chlorpromazine into sulfates so they can be safely eliminated from the body.
Sulfoxidation is another reaction catalyzed by POMs (Poly OxoMetalates). This catalysis is applicable
not only to the production of sulfoxides, which are generally more expensive than the corresponding
sulfones, there is also a large interest in their use as detoxifying agents. Mustard gas, dichloroethyl
sulfide, is catalytically oxidized by some POMs to form the much less dangerous sulfoxide. These
catalysts must proceed with virtually complete selectivity for the sulfoxide, because over oxidation
can lead to the sulfone, which is more toxic than the sulfide itself. There is current research underway
to attach these POMs to support structures such as silica or cotton . These types of materials could
then be placed in soldiers’ uniforms to help protect them from mustard gas exposure. Sulfides also
exist as atmospheric pollutants, so there is also a civilian interest in these materials as air purifiers.
n-oxidation
An amine oxide, also known as amine-N-oxide and N-oxide, is a chemical compound that contains
the functional group R3N+-O− (sometimes written as R3N=O or R3N→O). In the strict sense the term
amine oxide applies only to oxides of tertiary amines including nitrogen-containing aromatic
compounds like pyridine, but is sometimes also used for the analogous derivatives of primary and
secondary amines.
Amine oxides are used as protecting group for amines and as chemical intermediates. Long-chain
alkyl amine oxides are used as nonionic surfactants and foam stabilizers.
Amine oxide are highly polar molecules have a high polarity close to that of quaternary ammonium
salts. Small amine oxides are very hydrophilic and have an excellent water solubility and a very poor
solubility in most organic solvents.
Amine oxides are weak bases with a pKa of around 4.5 that form R3N+-OH, cationic hydroxylamines,
upon protonation at a pH below their pKa.
Pyridine N-oxide is a crystalline solid with melting point 62-67°C and soluble in water NMethylmorpholine N-oxide is an oxidant.
Epoxidation
An epoxide is a cyclic ether with only three ring atoms. This ring approximately is an equilateral
triangle (i.e., its bond angles are about 60°) which makes it highly strained. The strained ring makes
epoxides more reactive than other ethers, especially towards nucleophiles. Simple epoxides are
named from the parent compound ethylene oxide or oxirane, such as in chloromethyloxirane. As a
functional group epoxides obtain the epoxy prefix such as in the compound 1,2-epoxycycloheptane
which can also be called cycloheptene epoxide.
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A polymer containing unreacted epoxide units is called a polyepoxide or an epoxy. Epoxy resins are
used as adhesives and structural materials. Polymerization of an epoxide gives a polyether, for
example ethylene oxide polymerizes to give polyethylene glycol, also known as polyethylene oxide.
Epoxides are usually created by one of the following reactions:
Olefin peroxidation
Olefin peroxidation, also known as the Prilezhaev reaction involves the oxidation of an alkene with a
peroxide, usually a peroxyacid like m-CPBA or with a dioxirane like DMDO. An example is the
epoxidation of styrene with perbenzoic acid to styrene oxide.
The reaction proceeds via what is commonly known as the Butterfly Mechanism.It is easiest to
consider the oxygen to be an electrophile, and the alkene a nucleophile, although they both operate in
that capacity, and the reaction is considered to be concerted (the numbers in the mechanism below are
for simplification).
Related processes include some catalytic enantioselective reactions, such as the:
Sharpless epoxidation
Jacobsen epoxidation
Shi epoxidation
Intramolecular SN2 substitution
This method is a variant of the Williamson ether synthesis. In this case, the alkoxide ion and the
halide are right next to each other in the same molecule (such compounds are generically called
halohydrins), which makes this a simple ring closure reaction. For example, with 2-chloropropanol.
Johnson-Corey-Chaykovsky reaction
In the Johnson-Corey-Chaykovsky reaction epoxides are generated from carbonyl groups and
sulfonium ylides.
Reactions
Typical epoxide reactions are listed below.
Nucleophilic addition to an epoxide can be base or acid catalyzed.
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Under acidic conditions, the nucleophile attacks the carbon that will form the most stable carbocation,
i.e. the most substituted carbon (similar to a halonium ion). Under basic conditions, the nucleophile
attacks the least substituted carbon, in accordance with standard SN2 nuclephilic addition reaction
process.
Hydrolysis of an epoxide in presence of an acid catalyst generates a glycol. The hydrolysis process of
epoxides can be considered to be the nucleophilic addition of water to the epoxide under acidic
conditions.
Reduction of an epoxide with lithium aluminium hydride and water generates an alcohol. This
reduction process can be considered to be the nucleophilic addition of hydride (H-) to the epoxide
under basic conditions.
Reduction with tungsten hexachloride and n-butyllithium generates the alkene. This reaction in effect
is a de-epoxidation.
polyethers
]
Johnson-Corey-Chaykovsky reaction
In the Johnson-Corey-Chaykovsky reaction epoxides are generated from carbonyl groups and
sulfonium ylides.
Reactions
Typical epoxide reactions are listed below.
Nucleophilic addition to an epoxide can be base or acid catalyzed.
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Under acidic conditions, the nucleophile attacks the carbon that will form the most stable carbocation,
i.e. the most substituted carbon (similar to a halonium ion). Under basic conditions, the nucleophile
attacks the least substituted carbon, in accordance with standard SN2 nuclephilic addition reaction
process.
Hydrolysis of an epoxide in presence of an acid catalyst generates a glycol. The hydrolysis process of
epoxides can be considered to be the nucleophilic addition of water to the epoxide under acidic
conditions.
Reduction of an epoxide with lithium aluminium hydride and water generates an alcohol. This
reduction process can be considered to be the nucleophilic addition of hydride (H-) to the epoxide
under basic conditions.
Reduction with tungsten hexachloride and n-butyllithium generates the alkene. This reaction in effect
is a de-epoxidation.