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A generic epoxide.

An epoxide is a cyclic ether with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale for many applications. In general, low molecular weight epoxides are colourless and nonpolar, and often volatile.[1]


A compound containing the epoxide functional group can be called an epoxy, epoxide, oxirane, and ethoxyline. Simple epoxides are often referred to as oxides. Thus, the epoxide of ethylene (C2H4) is ethylene oxide (C2H4O). Many compounds have trivial names; for instance, ethylene oxide is called "oxirane". Some names emphasize the presence of the epoxide functional group, as in the compound 1,2-epoxyheptane, which can also be called 1,2-heptene oxide.




Heterogeneously catalyzed oxidation of alkenes[edit]




Olefin oxidation using organic peroxides and metal catalysts[edit]





Olefin peroxidation using peroxycarboxylic acids[edit]

More typically for laboratory operations, the Prilezhaev reaction is employed.[8][9] This approach involves the oxidation of the alkene with a peroxyacid such as m-CPBA. Illustrative is the epoxidation of styrene with perbenzoic acid to styrene oxide:[10]

Prilezhaev Reaction

The reaction proceeds via what is commonly known as the "Butterfly Mechanism".[11] The peroxide is viewed as an electrophile, and the alkene a nucleophile. The reaction is considered to be concerted (the numbers in the mechanism below are for simplification).The butterfly mechanism allows ideal positioning of the O-O sigma star orbital for C-C Pi electrons to attack.[12] Because two bonds are broken and formed to the epoxide oxygen, this is formally an example of a coarctate transition state.

Butterfly Mechanism


Homogeneously catalysed asymmetric epoxidations[edit]



The Sharpless epoxidation reaction is one of the premier enantioselective chemical reactions. It is used to prepare 2,3-epoxyalcohols from primary and secondary allylic alcohols.[15][16]


Intramolecular SN2 substitution[edit]

This method involves dehydrohalogenation. It is a variant of the Williamson ether synthesis. In this case, an alkoxide ion intramolecularly displaces chloride. The precursor compounds are called halohydrins.[18] Starting with propylene chlorohydrin, most of the world's supply of propylene oxide arises via this route.[7]

Methyloxirane from 2-chloropropionic acid.png



Nucleophilic epoxidation[edit]

Electron-deficient olefins, such as enones and acryl derivatives can be epoxidized using nucleophilic oxygen compounds such as peroxides. The reaction is a two-step mechanism. First the oxygen performs a nucleophilic conjugate addition to give a stabilized carbanion. This carbanion then attacks the same oxygen atom, displacing a leaving group from it, to close the epoxide ring.




Ring-opening reactions dominate the reactivity of epoxides.

Hydrolysis and addition of nucleophiles[edit]

Two pathways for the hydrolysis of an epoxide.


Polymerization and oligomerization[edit]

Polymerization of epoxides gives polyethers. For example ethylene oxide polymerizes to give polyethylene glycol, also known as polyethylene oxide. The reaction of an alcohol or a phenol with ethylene oxide, ethoxylation, is widely used to produce surfactants:[21]

ROH + n C2H4O → R(OC2H4)nOH

With anhydrides, epoxides give polyesters.[22]


Epoxides can be deoxygenated using oxophilic reagents. This reaction can proceed with loss or retention of configuration.[23] The combination of tungsten hexachloride and n-butyllithium gives the alkene.[24]

Other reactions[edit]


Ethylene oxide is widely used to generate detergents and surfactants by ethoxylation. Its hydrolysis affords ethylene glycol. It is also used for sterilisation of medical instruments and materials.



Epoxides are alkylating agents, making many of them highly toxic.[28]

See also[edit]


  1. ^ Guenter Sienel; Robert Rieth; Kenneth T. Rowbottom. "Epoxides". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a09_531.
  3. ^ Sajkowski, D. J.; Boudart, M. (1987). "Structure Sensitivity of the Catalytic Oxidation of Ethene by Silver". Catalysis Reviews. 29 (4): 325–360. doi:10.1080/01614948708078611.
  9. ^ Nikolaus Prileschajew (1909). "Oxydation ungesättigter Verbindungen mittels organischer Superoxyde" [Oxidation of unsaturated compounds by means of organic peroxides]. Berichte der Deutschen Chemischen Gesellschaft (in German). 42 (4): 4811–4815. doi:10.1002/cber.190904204100.
  15. ^ Katsuki, T.; Sharpless, K. B. (1980). "The first practical method for asymmetric epoxidation". J. Am. Chem. Soc. 102 (18): 5974–5976. doi:10.1021/ja00538a077.
  16. ^ Hill, J. G.; Sharpless, K. B.; Exon, C. M.; Regenye, R. Org. Synth., Coll. Vol. 7, p. 461 (1990); Vol. 63, p. 66 (1985). (Article Archived 2013-09-27 at the Wayback Machine)
  17. ^ a b Pham, Ha Q.; Marks, Maurice J. (2005). "Epoxy Resins". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a09_547.pub2. ISBN 978-3527306732.
  20. ^ Boron WF (2003). Medical Physiology: A Cellular And Molecular Approach. Elsevier/Saunders. p. 108. ISBN 978-1-4160-2328-9.
  21. ^ Kosswig, Kurt (2002). "Surfactants". In Elvers, Barbara; et al. (eds.). Ullmann's Encyclopedia of Industrial Chemistry. Weinheim, GER: Wiley-VCH. doi:10.1002/14356007.a25_747. ISBN 978-3527306732.
  22. ^ Julie M. Longo; Maria J. Sanford; Geoffrey W. Coates (2016). "Ring-Opening Copolymerization of Epoxides and Cyclic Anhydrides with Discrete Metal Complexes: Structure–Property Relationships". Chem. Rev. 116 (24): 15167–15197. doi:10.1021/acs.chemrev.6b00553. PMID 27936619.
  23. ^ Takuya Nakagiri, Masahito Murai, and Kazuhiko Takai (2015). "Stereospecific Deoxygenation of Aliphatic Epoxides to Alkenes under Rhenium Catalysis". Org. Lett. 17: 3346–3349. doi:10.1021/acs.orglett.5b01583.CS1 maint: Uses authors parameter (link)
  24. ^ K. Barry Sharpless, Martha A. Umbreit (1981). "Deoxygenation of Epoxides with Lower Valent Tungsten Halides: trans-Cyclododecene". Org. Synth. 60: 29. doi:10.15227/orgsyn.060.0029.
  25. ^ Bruce Rickborn and Wallace E. Lamke (1967). "Reduction of epoxides. II. The lithium aluminum hydride and mixed hydride reduction of 3-methylcyclohexene oxide". J. Org. Chem. 32 (3): 537–539. doi:10.1021/jo01278a005.