Difference between revisions of "Epoxide" - New World Encyclopedia

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[[Image:glycidol.png|thumb|right|The chemical structure of the epoxide [[glycidol]], a common chemical intermediate.]]
 
[[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]], that is, 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''.
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An '''epoxide''' is a cyclic [[ether]] with only three ring atoms. The simplest epoxide is [[ethylene oxide]], also known as ''oxirane'', which is regarded as the "parent" compound. Thus epoxides are also called ''oxiranes''. Epoxides are more reactive than ordinary ethers.
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This ring approximately is an [[equilateral triangle]], that is, 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.
 
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.

Revision as of 14:07, 22 September 2008

File:Glycidol.png
The chemical structure of the epoxide glycidol, a common chemical intermediate.

An epoxide is a cyclic ether with only three ring atoms. The simplest epoxide is ethylene oxide, also known as oxirane, which is regarded as the "parent" compound. Thus epoxides are also called oxiranes. Epoxides are more reactive than ordinary ethers.

This ring approximately is an equilateral triangle, that is, 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.

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 (oxiranes) are three-membered cyclic ethers that are easily prepared from alkenes by reaction with peracids. Because of the large angle strain in this small ring, epoxides undergo acid and base-catalyzed C–O bond cleavage more easily than do larger ring ethers."

Nomenclature

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.

A polymer containing unreacted epoxide units is called a polyepoxide or an epoxy.

Synthesis

Epoxides are usually produced by one of the reactions given below.

Olefin peroxidation

Olefin peroxidation, also known as the Prilezhaev reaction,[1][2] involves oxidation of an alkene with a peroxide, usually a peroxyacid like meta-chloroperoxybenzoic acid (m-CPBA) or with a dioxirane such as dimethyldioxirane (DMDO). An example is the epoxidation of styrene with perbenzoic acid to styrene oxide:[3]

Prilezhaev Reaction.

The reaction proceeds via what is commonly known as the Butterfly Mechanism.[4] It is easiest to consider the oxygen as an electrophile and the alkene as a nucleophile, although they both operate in that capacity, and the reaction is thought to be concerted. (The numbers in the mechanism below are for simplification.)

Butterfly Mechanism

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:[5]

Methyloxirane from 2-chloroproprionic acid.png

Johnson-Corey-Chaykovsky reaction

In the Johnson-Corey-Chaykovsky reaction, epoxides are generated from carbonyl groups and sulfonium ylides.

Reactions

The three-membered ring of epoxide is approximately an equilateral triangle, that is, its bond angles are about 60°, which makes it highly strained. The strained ring makes epoxides more reactive than other ethers, especially towards nucleophiles. Typical epoxide reactions are noted below.

  • Nucleophilic addition to an epoxide can be catalyzed by a base or an acid.
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 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 aluminum 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:[6]
De-epoxidation with tungsten hexachloride / n-butyllithium.

See also

Notes

  1. March, Jerry. 1985. Advanced Organic Chemistry: Reactions, Mechanisms and Structure. 3rd ed. John Wiley & Sons. ISBN 0471854727.
  2. Prileschajew, Nikolaus. 1909. Oxydation ungesättigter Verbindungen mittels organischer Superoxyde. Berichte der deutschen chemischen Gesellschaft. 42(4): 4811–4815. (doi:10.1002/cber.190904204100.)
  3. Hibbert, Harold, and Pauline Burt. 1941. Styrene Oxide. Org. Synth. Coll. Vol. 1: 494. Retrieved September 22, 2008.
  4. Bartlett. 1950. Rec. Chem. Prog. 11:47.
  5. Koppenhoefer, B., and V. Schurig. 1993. (R)-Alkyloxiranes of High Enantiomeric Purity from (S)-2-Chloroalkanoic Acids via (S)-2-Chloro-1-Alkanols: (R)-Methyloxirane. Org. Synth. Coll. Vol. 8: 434. Retrieved September 22, 2008.
  6. Sharpless, K. Barry, Martha A. Umbreit, Marjorie T. Nieh, and Thomas C. Flood. 1972. Lower valent tungsten halides. New class of reagents for deoxygenation of organic molecules. J. Am. Chem. Soc. 94(18): 6538-6540. (doi:10.1021/ja00773a045.)

References
ISBN links support NWE through referral fees

  • March, Jerry. 1985. Advanced Organic Chemistry: Reactions, Mechanisms and Structure. 3rd ed. John Wiley & Sons. ISBN 0471854727.
  • McMurry, John. 2004. Organic Chemistry. 6th ed. Belmont, CA: Brooks/Cole. ISBN 0534420052.
  • Morrison, Robert T., and Robert N. Boyd. 1992. Organic Chemistry. 6th ed. Englewood Cliffs, NJ: Prentice Hall. ISBN 0136436692.
  • Solomons, T.W. Graham, and Craig B. Fryhle. 2004. Organic Chemistry. 8th ed. Hoboken, NJ: John Wiley. ISBN 0471417998.
  • Streitwieser, Andrew, and Clayton H. Heathcock. 1976. Introduction to Organic Chemistry. New York: Macmillan. ISBN 0024180106.

External links

  • Ethylene Oxide National Institute for Occupational Safety and Health. Retrieved September 22, 2008.

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