Epoxide 355859 224094562 2008-07-07T07:53:12Z Rifleman 82 1255637 Removing link to empty page [[Polyethylene oxide]] using [[:en:Wikipedia:Tools/Navigation_popups|popups]] [[Image:glycidol.png|thumb|right|The chemical structure of the epoxide [[glycidol]], a common chemical intermediate]] 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 [[ring strain|strained]]. The strained ring makes epoxides more reactive than other ethers, especially towards [[nucleophile]]s. 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 (linguistics)|prefix]] such as in the compound ''1,2-epoxycycloheptane'' which can also be called ''cycloheptene epoxide''. A [[polymer]] containing unreacted epoxide units is called a ''polyepoxide'' or an ''[[epoxy]]''. Epoxy resins are used as [[adhesive]]s and structural materials. Polymerization of an epoxide gives a [[polyether]], for example [[ethylene oxide]] polymerizes to give [[polyethylene glycol]], also known as polyethylene oxide. ==Synthesis==<!-- This section is linked from [[Organic reaction]] --> Epoxides are usually created by one of the following reactions: ===Olefin peroxidation=== Olefin peroxidation, also known as the '''Prilezhaev reaction''' <ref>{{JerryMarch}}</ref><ref>{{cite journal | author = Nikolaus Prileschajew | journal = Berichte der deutschen chemischen Gesellschaft | volume = 42 | issue = 4 | pages = 4811–4815 | title = Oxydation ungesättigter Verbindungen mittels organischer Superoxyde | doi = 10.1002/cber.190904204100 | year = 1909}}</ref> involves the oxidation of an [[alkene]] with a [[peroxide]], usually a [[peroxyacid]] like [[Meta-Chloroperoxybenzoic acid|m-CPBA]] or with a [[dioxirane]] like [[Dimethyldioxirane|DMDO]]. An example is the epoxidation of [[styrene]] with [[perbenzoic acid]] to [[styrene oxide]]:<ref>{{OrgSynth | author = Harold Hibbert and Pauline Burt | title = Styrene Oxide | collvol = 1 | collvolpages = 494 | year = 1941 | prep = cv1p0494}}</ref> :[[Image:PrilezhaevReaction.svg|Prilezhaev Reaction]] The reaction proceeds via what is commonly known as the '''Butterfly Mechanism'''.<ref>Bartlett ''Rec. Chem. Prog'' '''1950''', ''11'' 47.</ref> 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). :[[Image:ButterflyMech.png|Butterfly Mechanism]] Related processes include some catalytic [[enantioselective]] reactions, such as the: *[[Sharpless epoxidation]] * [[Jacobsen epoxidation]] * [[Shi epoxidation]] ===Intramolecular S<sub>N</sub>2 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 [[halohydrin]]s), which makes this a simple ring closure reaction. For example, with [[2-chloropropanol]]:<ref>{{OrgSynth | author = Koppenhoefer, B.; Schurig, V. | title = (R)-Alkyloxiranes of High Enantiomeric Purity from (S)-2-Chloroalkanoic Acids via (S)-2-Chloro-1-Alkanols: (R)-Methyloxirane | collvol = 8 | collvolpages = 434 | year = 1993 | prep = cv8p0434}}</ref> [[Image:Methyloxirane_from_2-chloroproprionic_acid.png|400px]] ===Johnson-Corey-Chaykovsky reaction=== In the [[Johnson-Corey-Chaykovsky reaction]] epoxides are generated from [[carbonyl]] groups and [[sulfonium ylide]]s. == Reactions ==<!-- This section is linked from [[Organic reaction]] --> Typical epoxide reactions are listed below. * [[Nucleophilic addition]] to an epoxide can be base or acid catalyzed. :[[Image:EpoxOpen.png]] :* 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 S<sub>N</sub>2 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 [[acid catalysis|acidic]] conditions. * [[organic reduction|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''':<ref>{{cite journal | title = Lower valent tungsten halides. New class of reagents for deoxygenation of organic molecules | author = [[K. Barry Sharpless]], Martha A. Umbreit, Marjorie T. Nieh, Thomas C. Flood | journal = [[J. Am. Chem. Soc.]] | year = 1972 | volume = 94 | issue = 18 | pages = 6538-6540 | doi = 10.1021/ja00773a045}}</ref> :[[Image:De-epoxidation.png|400px|De-epoxidation with tungsten hexachloride / n-butyllithium]] == See also == * [[polyether]]s == References == {{reflist}} [[Category:functional groups]] [[Category:ethers]] [[Category:Epoxides]] [[de:Epoxide]] [[es:Epóxido]] [[fr:Époxyde]] [[it:Epossidi]] [[mk:Епоксид]] [[nl:Epoxide]] [[ja:エポキシド]] [[pl:Epitlenki]] [[pt:Epóxido]] [[sv:Epoxid]] [[zh:环氧化合物]]