epoxide

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.

A polymer formed from epoxide precursors is called an epoxy. However, few if any of the epoxy groups in the resin survive the curing process.

The dominant epoxides industrially are ethylene oxide and propylene oxide, which are produced respectively on the scales of approximately 15 and 3 million tonnes/year.{{Ullmann |author1=Siegfried Rebsdat |author2=Dieter Mayer |title=Ethylene Oxide |doi=10.1002/14356007.a10_117 }}

Aside from ethylene oxide, most epoxides are generated when peroxidized reagents donate a single oxygen atom to an alkene. Safety considerations weigh on these reactions because organic peroxides are prone to spontaneous decomposition or even combustion.

Both t-butyl hydroperoxide and ethylbenzene hydroperoxide can be used as oxygen sources during propylene oxidation (although a catalyst is required as well, and most industrial producers use dehydrochlorination instead).Dietmar Kahlich, Uwe Wiechern, Jörg Lindner "Propylene Oxide" in Ullmann's Encyclopedia of Industrial Chemistry, 2002 by Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a22_239}}

The ethylene oxide industry generates its product from reaction of ethylene and oxygen. Modified heterogeneous silver catalysts are typically employed.{{cite journal|journal = Catalysis Reviews|title = Structure Sensitivity of the Catalytic Oxidation of Ethene by Silver|last1=Sajkowski|first1= D. J.|last2 = Boudart|first2 = M.|date = 1987|volume =29|issue = 4|pages = 325–360|doi = 10.1080/01614948708078611}} According to a reaction mechanism suggested in 1974{{cite journal

| author = Kilty P. A.|author2= Sachtler W. M. H.

| title = The mechanism of the selective oxidation of ethylene to ethylene oxide

| doi=10.1080/01614947408079624

| journal = Catalysis Reviews: Science and Engineering

| year = 1974

| volume = 10

| pages = 1–16

}} at least one ethylene molecule is totally oxidized for every six that are converted to ethylene oxide: 7 H2C=CH2 + 6 O2 -> 6 C2H4O + 2 CO2 + 2 H2O

Only ethylene produces an epoxide during incomplete combustion. Other alkenes fail to react usefully, even propylene, though TS-1 supported Au catalysts can selectively epoxidize propylene.{{cite journal |title=The Production of Propene Oxide: Catalytic Processes and Recent Developments|first1=T. Alexander|last1=Nijhuis|first2=Michiel|last2=Makkee|first3=Jacob A.|last3=Moulijn|first4=Bert M. |last4 = Weckhuysen |date=1 May 2006|journal=Industrial & Engineering Chemistry Research |volume=45 |issue=10 |pages=3447–3459|doi=10.1021/ie0513090|hdl = 1874/20149|s2cid=94240406 |hdl-access=free}}

Metal complexes are useful catalysts for epoxidations involving hydrogen peroxide and alkyl hydroperoxides. Metal-catalyzed epoxidations were first explored using tert-butyl hydroperoxide (TBHP).{{cite journal | author = Indictor N., Brill W. F. | year = 1965 | title = Metal Acetylacetonate Catalyzed Epoxidation of Olefins with t-Butyl Hydroperoxide| journal = J. Org. Chem. | volume = 30 | issue = 6| page = 2074 | doi = 10.1021/jo01017a520 }} Association of TBHP with the metal (M) generates the active metal peroxy complex containing the MOOR group, which then transfers an O center to the alkene.{{cite journal | author = Thiel W. R. | year = 1997 | title = Metal catalyzed oxidations. Part 5. Catalytic olefin epoxidation with seven-coordinate oxobisperoxo molybdenum complexes: a mechanistic study | journal = Journal of Molecular Catalysis A: Chemical | volume = 117 | pages = 449–454 | doi = 10.1016/S1381-1169(96)00291-9 }}

:File:SimpleMOORexpxCyc2.svg

Vanadium(II) oxide catalyzes the epoxidation at specifically less-substituted alkenes.{{cite journal|date=25 Sep 2006|first=Douglass|last=Taber|title=Selective reactions of Alkenes|journal=Organic Chemistry Highlights|url=https://www.organic-chemistry.org/Highlights/2006/25September.shtm}}

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.

Peroxycarboxylic acids, which are more electrophilic than other peroxides, convert alkenes to epoxides without the intervention of metal catalysts. In specialized applications, dioxirane reagents (e.g. dimethyldioxirane) perform similarly, but are more explosive.

Typical laboratory operations employ the Prilezhaev reaction.March, Jerry. 1985. Advanced Organic Chemistry, Reactions, Mechanisms and Structure. 3rd ed. John Wiley & Sons. {{ISBN|0-471-85472-7}}.{{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

| trans-title = Oxidation of unsaturated compounds by means of organic peroxides

| doi = 10.1002/cber.190904204100

| year = 1909

| language = de

| url = https://zenodo.org/record/1426367}} This approach involves the oxidation of the alkene with a peroxyacid such as mCPBA. Illustrative is the epoxidation of styrene with perbenzoic acid to styrene oxide:{{OrgSynth | author = Harold Hibbert and Pauline Burt | title = Styrene Oxide | collvol = 1 | collvolpages = 494 | year = 1941 | prep = cv1p0494}}

:Prilezhaev Reaction

The stereochemistry of the reaction is quite sensitive. Depending on the mechanism of the reaction and the geometry of the alkene starting material, cis and/or trans epoxide diastereomers may be formed. In addition, if there are other stereocenters present in the starting material, they can influence the stereochemistry of the epoxidation.

The reaction proceeds via what is commonly known as the "Butterfly Mechanism".{{cite journal | author = Paul D. Bartlett | title = Recent work on the mechanisms of peroxide reactions | journal = Record of Chemical Progress | year = 1950 | volume = 11 | pages = 47–51}} The peroxide is viewed as an electrophile, and the alkene a nucleophile. The reaction is considered to be concerted. The butterfly mechanism allows ideal positioning of the {{chem2|O\sO}} sigma star orbital for {{chem2|C\sC}} π electrons to attack.{{cite book|author=John O. Edwards|title=Peroxide Reaction Mechanisms | publisher=Interscience, New York| year = 1962 | pages = 67–106}} Because two bonds are broken and formed to the epoxide oxygen, this is formally an example of a coarctate transition state.

:File:Epoxidation butterfly mechanism.svg

Chiral epoxides are produced by epoxidation of prochiral alkenes. When the catalyst is chiral or the alkene is chiral, then asymmetric epoxidation becomes possible. Prominent methodologies are the Sharpless epoxidation, the Jacobsen epoxidation, and the Shi epoxidation.{{cite journal |last1 = Berrisford |first1 = D. J. |last2 =Bolm |first2=C. |last3=Sharpless |first3=K. B. | year = 2003 | title = Ligand-Accelerated Catalysis | journal = Angew. Chem. Int. Ed. Engl. | volume = 95 | issue = 10 | pages = 1059–1070 | doi = 10.1002/anie.199510591 }}

File:Epichlorohydryna.svg, is prepared by the chlorohydrin method. It is a precursor in the production of epoxy resins.{{cite encyclopedia|last1=Pham|first1=Ha Q.|last2=Marks|first2=Maurice J.|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|doi=10.1002/14356007.a09_547.pub2|publisher=Wiley-VCH|year=2005|isbn=978-3527306732|chapter=Epoxy Resins}}]]

Halohydrins react with base to give epoxides.{{OrgSynth | author = Koppenhoefer, B. |author2=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}} The reaction is spontaneous because the energetic cost of introducing the ring strain (13 kcal/mol) is offset by the larger bond enthalpy of the newly introduced C-O bond (when compared to that of the cleaved C-halogen bond).

Formation of epoxides from secondary halohydrins is predicted to occur faster than from primary halohydrins due to increased entropic effects in the secondary halohydrin, and tertiary halohydrins react (if at all) extremely slowly due to steric crowding.

{{cite journal | author = Silva, P.J. | year = 2023 | title = Computational insights into the spontaneity of epoxide formation from halohydrins and other mechanistic details of Williamson's ether synthesis | journal = Chem. J. Mold. | volume = 18 | issue = 2 | pages = 87–95 | doi = 10.19261/cjm.2023.1083 | doi-access = free }}

Starting with propylene chlorohydrin, most of the world's supply of propylene oxide arises via this route.

File:Methyloxirane from 2-chloropropionic acid.png

An intramolecular epoxide formation reaction is one of the key steps in the Darzens reaction.

In the Johnson–Corey–Chaykovsky reaction epoxides are generated from carbonyl groups and sulfonium ylides. In this reaction, a sulfonium is the leaving group instead of chloride.

Epoxides are uncommon in nature. They arise usually via oxygenation of alkenes by the action of cytochrome P450.{{cite journal | author = Thibodeaux C. J. | year = 2012 | title = Enzymatic Chemistry of Cyclopropane, Epoxide, and Aziridine Biosynthesis | journal = Chem. Rev. | volume = 112 | issue = 3 | pages = 1681–1709 | doi = 10.1021/cr200073d | pmid = 22017381 | pmc = 3288687 }} (but see also the short-lived epoxyeicosatrienoic acids which act as signalling molecules.{{cite book | first = Walter F. | last = Boron | name-list-style = vanc | title = Medical Physiology: A Cellular And Molecular Approach | publisher = Elsevier/Saunders | year = 2003 | page = 108 | isbn = 978-1-4160-2328-9 }} and similar epoxydocosapentaenoic acids, and epoxyeicosatetraenoic acids.)

Arene oxides are intermediates in the oxidation of arenes by cytochrome P450. For prochiral arenes (naphthalene, toluene, benzoates, benzopyrene), the epoxides are often obtained in high enantioselectivity.

== Reactions ==

Ring-opening reactions dominate the reactivity of epoxides.

:File:Epoxide hydrolysis.svg

Epoxides react with a broad range of nucleophiles, for example, alcohols, water, amines, thiols, and even halides. With two often-nearly-equivalent sites of attack, epoxides exemplify "ambident substrates".{{March6th|page=517}} Ring-opening regioselectivity in asymmetric epoxides generally follows the S_N2 pattern of attack at the least-substituted carbon,{{cite book|title=Organic Synthesis: the disconnection approach|edition=2nd|first1=Stuart|last1=Warren|first2=Paul|last2=Wyatt|publisher=Wiley|year=2008|page=39}} but can be affected by carbocation stability under acidic conditions.{{cite web|url=https://www.ch.imperial.ac.uk/rzepa/blog/?p=10237|first=Henry|last=Rzepa|author-link=Henry Rzepa|website=Chemistry with a twist|title=How to predict the regioselectivity of epoxide ring opening|date=28 April 2013}} This class of reactions is the basis of epoxy glues and the production of glycols.

Lithium aluminium hydride or aluminium hydride both reduce epoxides through a simple nucleophilic addition of hydride (H⁻); they produce the corresponding alcohol.{{cite journal | title = Reduction of epoxides. II. The lithium aluminum hydride and mixed hydride reduction of 3-methylcyclohexene oxide | author = Bruce Rickborn and Wallace E. Lamke | year = 1967 | volume = 32 | issue = 3 | pages = 537–539 | journal = J. Org. Chem. | doi = 10.1021/jo01278a005}}

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:{{cite encyclopedia| author = Kosswig, Kurt | year = 2002 | encyclopedia= Ullmann's Encyclopedia of Industrial Chemistry | chapter = Surfactants |editor = Elvers, Barbara |display-editors=etal | doi = 10.1002/14356007.a25_747 | location = Weinheim, GER | publisher = Wiley-VCH | ref = published online, 15 June 2000 | isbn = 978-3527306732 }}

:ROH + n C₂H₄O → R(OC₂H₄)_nOH

With anhydrides, epoxides give polyesters.{{cite journal|title=Ring-Opening Copolymerization of Epoxides and Cyclic Anhydrides with Discrete Metal Complexes: Structure–Property Relationships|author=Julie M. Longo |author2=Maria J. Sanford |author3=Geoffrey W. Coates|journal=Chem. Rev.|year=2016|volume=116|issue=24|pages=15167–15197|doi=10.1021/acs.chemrev.6b00553|pmid=27936619}}

Lithiation cleaves the ring to β-lithioalkoxides.{{cite journal | title = 1,3-Diols From Lithium Β-lithioalkoxides Generated By The Reductive Lithiation Of Epoxides: 2,5-dimethyl-2,4-hexanediol |author1=B. Mudryk |author2=T. Cohen | journal = Org. Synth. | year = 1995 | volume = 72 | pages = 173 | doi = 10.15227/orgsyn.072.0173}}

Epoxides can be deoxygenated using oxophilic reagents, with loss or retention of configuration.{{cite journal|title=Stereospecific Deoxygenation of Aliphatic Epoxides to Alkenes under Rhenium Catalysis|author1=Takuya Nakagiri |author2=Masahito Murai |author3=Kazuhiko Takai |journal=Org. Lett.|year=2015|volume=17|issue=13|pages=3346–9|doi=10.1021/acs.orglett.5b01583|pmid=26065934}} The combination of tungsten hexachloride and n-butyllithium gives the alkene.{{cite journal | title = Deoxygenation of Epoxides with Lower Valent Tungsten Halides: trans-Cyclododecene | author = K. Barry Sharpless, Martha A. Umbreit | journal = Org. Synth. | year = 1981 | volume = 60| page = 29 | doi = 10.15227/orgsyn.060.0029}}{{cite journal | title = Lower valent tungsten halides. New class of reagents for deoxygenation of organic molecules |author1=K. Barry Sharpless |author1-link=Karl Barry Sharpless |author2=Martha A. Umbreit |author3=Marjorie T. Nieh |author4=Thomas C. Flood | journal = J. Am. Chem. Soc. | year = 1972 | volume = 94 | issue = 18 | pages = 6538–6540 | doi = 10.1021/ja00773a045}}

When treated with thiourea, epoxides convert to the episulfide (thiiranes).

• Epoxides undergo ring expansion reactions, illustrated by the insertion of carbon dioxide to give cyclic carbonates.
• An epoxide adjacent to an alcohol can undergo the Payne rearrangement in base.

{{Gallery

|title=Illustrative epoxides

|width=220 |height=100

|align=

|footer=

|File:Bisphenol A diglycidyl ether 200.svg

|Bisphenol A diglycidyl ether is a component in common household "epoxy".

|File:Glycidol structure.svg

|The chemical structure of the epoxide glycidol, a common chemical intermediate.

|File:Epothilone A B.svg

|Epothilones are naturally occurring epoxides.

|File:Diepoxyester.svg|3,4-Epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, precursor to coatings.{{cite journal |last1=Sasaki |first1=Hiroshi |title=Curing properties of cycloaliphatic epoxy derivatives |journal=Progress in Organic Coatings |date=February 2007 |volume=58 |issue=2–3 |pages=227–230 |doi=10.1016/j.porgcoat.2006.09.030}}

|File:Epoxidized linolein.svg

|Epoxidized linolein, a major component of epoxidized soybean oil (ESBO), a commercially important plasticizer.

|File:Oxepin-benzene oxide.png|Benzene oxide exists in equilibrium with the oxepin isomer.

}}

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.

The reaction of epoxides with amines is the basis for the formation of epoxy glues and structural materials. A typical amine-hardener is triethylenetetramine (TETA).

Epoxides are alkylating agents, making many of them highly toxic.{{cite journal |title= Mechanistic approaches for evaluating the toxicity of reactive organochlorines and epoxides in green algae |first1= Christian |last1= Niederer |first2= Renata |last2= Behra |first3= Angela |last3= Harder |first4= René P. |last4= Schwarzenbach |first5= Beate I. |last5= Escher |journal= Environmental Toxicology and Chemistry |volume= 23 |issue= 3 |pages= 697–704 |year= 2004 |doi= 10.1897/03-83 |pmid= 15285364 |s2cid= 847639 }}

• Epoxide hydrolase
• Juliá–Colonna epoxidation
• Aziridine (nitrogen analogue) and thiirane (sulfur one)
• Cyclopropane
• Oxaziridine (cyclic three-membered ring with C, N, and O)

• {{Cite book |last1=Massingill |first1=J. L. |chapter=Epoxy Resins |date=2000-01-01 |chapter-url=https://www.sciencedirect.com/science/article/pii/B9780080434179500234 |title=Applied Polymer Science: 21st Century |pages=393–424 |editor-last=Craver |editor-first=Clara D. |access-date=2023-12-20 |place=Oxford |publisher=Pergamon |doi=10.1016/b978-008043417-9/50023-4 |isbn=978-0-08-043417-9 |last2=Bauer |first2=R. S. |editor2-last=Carraher |editor2-first=Charles E.}}

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