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Enol ether

January 01, 1970

In organic chemistry an enol ether is an alkene with an alkoxy substituent.[1] The general structure is R2C=CR-OR where R = H, alkyl or aryl. A common subfamily of enol ethers are vinyl ethers, with the formula ROCH=CH2. Important enol ethers include the reagent 3,4-dihydropyran and the monomers methyl vinyl ether and ethyl vinyl ether.

The structure of a typical enol ether group
Enamines are chemically related to enol ethers.

Reactions and uses edit

Akin to enamines, enol ethers are electron-rich alkenes by virtue of the electron-donation from the heteroatom via pi-bonding. Enol ethers have oxonium ion character. By virtue of their bonding situation, enol ethers display distinctive reactivity. In comparison with simple alkenes, enol ethers exhibit enhanced susceptibility to attack by electrophiles such as Bronsted acids. Similarly, they undergo inverse demand Diels-Alder reactions.[2]

 

The reactivity of enol ethers is highly dependent on the presence of substituents alpha to oxygen. The vinyl ethers are susceptible to polymerization to give polyvinyl ethers.[3] They also react readily with thiols in the thiol-ene reaction to form thioethers. This makes enol ether-functionalized monomers ideal for polymerization with thiol-based monomers to form thiol-ene networks.[4]

Some vinyl ethers find some use as inhalation anesthetics. Enol ethers bearing α substituents do not polymerize readily. They are mainly of academic interest, e.g. as intermediates in the synthesis of more complex molecules.

The acid-catalyzed addition of hydrogen peroxide to vinyl ethers gives the hydroperoxide:[5]

C2H5OCH=CH2 + H2O2 → C2H5OCH(OOH)CH3

Nazi Germany used vinyl ether mixtures as rocket propellants during WWII, because their hypergolic combustion with a mixture of nitric and sulfuric acids is relatively insensitive to temperature.[6]

Preparation edit

Although enol ethers can be considered the ether of the corresponding enolates, they are not prepared by alkylation of enolates. Some enol ethers are prepared from saturated ethers by elimination reactions.[7]

 
Ethyl vinyl ether is a potent anesthetic.

Alternatively, vinyl ethers can be prepared from alcohols by iridium-catalyzed transesterification of vinyl esters, especially the widely available vinyl acetate:[8]

ROH + CH2=CHOAc → ROCH=CH2 + HOAc

Vinyl ethers can be prepared by reaction of acetylene and alcohols in presence of a base.[9]

Occurrence in nature edit

A prominent enol ether is phosphoenol pyruvate.[10]

The enzyme chorismate mutase catalyzes the Claisen rearrangement of the enol ether called chorismate to prephenate, an intermediate in the biosynthesis of phenylalanine and tyrosine.[11]

 
Chorismate mutase catalyzes a Claisen rearrangement

Batyl alcohol and related glycyl ethers are susceptible to dehydrogenation catalyzed unsaturases to give the vinyl ethers called plasmalogens:[12]

HOCH2CH(OH)CH2OC18H37 + [O] → HOCH2CH(OH)CH2OCH=CHC16H35 + H2O
 
General structure of strigolactones, a family of plant hormones.[13]

See also edit

References edit

  1. ^ Jonathan Clayden; Greeves, Nick; Stuart Warren (2012). Organic Chemistry (2nd ed.). Oxford University Press. p. 295. ISBN 978-0-19-927029-3.
  2. ^ Percy S. Manchand (2001). "Ethyl Vinyl Ether". EEROS. doi:10.1002/047084289X.re125. ISBN 0-471-93623-5.
  3. ^ Gerd Schröder (2012). "Poly(Vinyl Ethers)". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a22_011. ISBN 978-3527306732.
  4. ^ Hoyle, Charles E.; Bowman, Christopher N. (2010). "Thiol–Ene Click Chemistry". Angewandte Chemie International Edition. 49 (9): 1540–1573. doi:10.1002/anie.200903924.
  5. ^ Milas, Nicholas A.; Peeler, Robert L.; Mageli, Orville L. (1954). "Organic Peroxides. XIX. α-Hydroperoxyethers and Related Peroxides". Journal of the American Chemical Society. 76 (9): 2322–2325. doi:10.1021/ja01638a012.
  6. ^ Clark, John Drury. Ignition! (PDF). New Brunswick, NJ: Rutgers UP. p. 16. ISBN 0-8135-0725-1. LCCN 72-185390.
  7. ^ Carl Kaiser; Joseph Weinstock (1976). "Alkenes Via Hofmann Elimination: Use of Ion-exchange Resin for Preparation of Quaternary Ammonium Hydroxides: Diphenylmethyl Vinyl Ether". Org. Synth. 55: 3. doi:10.15227/orgsyn.055.0003.
  8. ^ Tomotaka Hirabayashi; Satoshi Sakaguchi; Yasutaka Ishii (2005). "Iridium-catalyzed Synthesis of Vinyl Ethers from Alcohols and Vinyl Acetate". Org. Synth. 82: 55. doi:10.15227/orgsyn.082.0055.
  9. ^ Ernst Hofmann; Hans‐Joachim Klimisch; René Backes; Regina Vogelsang; Lothar Franz; Robert Feuerhake (2011). "Vinyl Ethers". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a27_435.pub2. ISBN 978-3527306732.
  10. ^ Walsh, C.T.; Benson, T.E.; Kim, D.H.; Lees, W.J. (1996). "The versatility of phosphoenolpyruvate and its vinyl ether products in biosynthesis". Chemistry & Biology. 3 (2): 83–91. doi:10.1016/s1074-5521(96)90282-3. PMID 8807832.
  11. ^ Ganem, B. (1996). "The Mechanism of the Claisen Rearrangement: Déjà Vu All over Again". Angew. Chem. Int. Ed. Engl. 35 (9): 936–945. doi:10.1002/anie.199609361.
  12. ^ Taguchi, Hiroyasu; Armarego, Wilfred L. F. (1998). "Glyceryl-Ether Monooxygenase [EC 1.14.16.5]. A Microsomal Enzyme of Ether Lipid Metabolism". Medicinal Research Reviews. 18 (1): 43–89. doi:10.1002/(SICI)1098-1128(199801)18:1<43::AID-MED3>3.0.CO;2-S. PMID 9436181. S2CID 432376.
  13. ^ Umehara M, Cao M, Akiyama K, Akatsu T, Seto Y, Hanada A, et al. (June 2015). "Structural Requirements of Strigolactones for Shoot Branching Inhibition in Rice and Arabidopsis". Plant & Cell Physiology. 56 (6): 1059–72. doi:10.1093/pcp/pcv028. PMID 25713176.

January 01, 1970
enol, ether, organic, chemistry, enol, ether, alkene, with, alkoxy, substituent, general, structure, where, alkyl, aryl, common, subfamily, enol, ethers, vinyl, ethers, with, formula, roch, important, enol, ethers, include, reagent, dihydropyran, monomers, met. In organic chemistry an enol ether is an alkene with an alkoxy substituent 1 The general structure is R2C CR OR where R H alkyl or aryl A common subfamily of enol ethers are vinyl ethers with the formula ROCH CH2 Important enol ethers include the reagent 3 4 dihydropyran and the monomers methyl vinyl ether and ethyl vinyl ether The structure of a typical enol ether group Enamines are chemically related to enol ethers Contents 1 Reactions and uses 2 Preparation 3 Occurrence in nature 4 See also 5 ReferencesReactions and uses editAkin to enamines enol ethers are electron rich alkenes by virtue of the electron donation from the heteroatom via pi bonding Enol ethers have oxonium ion character By virtue of their bonding situation enol ethers display distinctive reactivity In comparison with simple alkenes enol ethers exhibit enhanced susceptibility to attack by electrophiles such as Bronsted acids Similarly they undergo inverse demand Diels Alder reactions 2 nbsp The reactivity of enol ethers is highly dependent on the presence of substituents alpha to oxygen The vinyl ethers are susceptible to polymerization to give polyvinyl ethers 3 They also react readily with thiols in the thiol ene reaction to form thioethers This makes enol ether functionalized monomers ideal for polymerization with thiol based monomers to form thiol ene networks 4 Some vinyl ethers find some use as inhalation anesthetics Enol ethers bearing a substituents do not polymerize readily They are mainly of academic interest e g as intermediates in the synthesis of more complex molecules The acid catalyzed addition of hydrogen peroxide to vinyl ethers gives the hydroperoxide 5 C2H5OCH CH2 H2O2 C2H5OCH OOH CH3 Nazi Germany used vinyl ether mixtures as rocket propellants during WWII because their hypergolic combustion with a mixture of nitric and sulfuric acids is relatively insensitive to temperature 6 Preparation editAlthough enol ethers can be considered the ether of the corresponding enolates they are not prepared by alkylation of enolates Some enol ethers are prepared from saturated ethers by elimination reactions 7 nbsp Ethyl vinyl ether is a potent anesthetic Alternatively vinyl ethers can be prepared from alcohols by iridium catalyzed transesterification of vinyl esters especially the widely available vinyl acetate 8 ROH CH2 CHOAc ROCH CH2 HOAc Vinyl ethers can be prepared by reaction of acetylene and alcohols in presence of a base 9 Occurrence in nature editA prominent enol ether is phosphoenol pyruvate 10 The enzyme chorismate mutase catalyzes the Claisen rearrangement of the enol ether called chorismate to prephenate an intermediate in the biosynthesis of phenylalanine and tyrosine 11 nbsp Chorismate mutase catalyzes a Claisen rearrangement Batyl alcohol and related glycyl ethers are susceptible to dehydrogenation catalyzed unsaturases to give the vinyl ethers called plasmalogens 12 HOCH2CH OH CH2OC18H37 O HOCH2CH OH CH2OCH CHC16H35 H2O nbsp General structure of strigolactones a family of plant hormones 13 See also editSilyl enol etherReferences edit Jonathan Clayden Greeves Nick Stuart Warren 2012 Organic Chemistry 2nd ed Oxford University Press p 295 ISBN 978 0 19 927029 3 Percy S Manchand 2001 Ethyl Vinyl Ether EEROS doi 10 1002 047084289X re125 ISBN 0 471 93623 5 Gerd Schroder 2012 Poly Vinyl Ethers Ullmann s Encyclopedia of Industrial Chemistry Weinheim Wiley VCH doi 10 1002 14356007 a22 011 ISBN 978 3527306732 Hoyle Charles E Bowman Christopher N 2010 Thiol Ene Click Chemistry Angewandte Chemie International Edition 49 9 1540 1573 doi 10 1002 anie 200903924 Milas Nicholas A Peeler Robert L Mageli Orville L 1954 Organic Peroxides XIX a Hydroperoxyethers and Related Peroxides Journal of the American Chemical Society 76 9 2322 2325 doi 10 1021 ja01638a012 Clark John Drury Ignition PDF New Brunswick NJ Rutgers UP p 16 ISBN 0 8135 0725 1 LCCN 72 185390 Carl Kaiser Joseph Weinstock 1976 Alkenes Via Hofmann Elimination Use of Ion exchange Resin for Preparation of Quaternary Ammonium Hydroxides Diphenylmethyl Vinyl Ether Org Synth 55 3 doi 10 15227 orgsyn 055 0003 Tomotaka Hirabayashi Satoshi Sakaguchi Yasutaka Ishii 2005 Iridium catalyzed Synthesis of Vinyl Ethers from Alcohols and Vinyl Acetate Org Synth 82 55 doi 10 15227 orgsyn 082 0055 Ernst Hofmann Hans Joachim Klimisch Rene Backes Regina Vogelsang Lothar Franz Robert Feuerhake 2011 Vinyl Ethers Ullmann s Encyclopedia of Industrial Chemistry Weinheim Wiley VCH doi 10 1002 14356007 a27 435 pub2 ISBN 978 3527306732 Walsh C T Benson T E Kim D H Lees W J 1996 The versatility of phosphoenolpyruvate and its vinyl ether products in biosynthesis Chemistry amp Biology 3 2 83 91 doi 10 1016 s1074 5521 96 90282 3 PMID 8807832 Ganem B 1996 The Mechanism of the Claisen Rearrangement Deja Vu All over Again Angew Chem Int Ed Engl 35 9 936 945 doi 10 1002 anie 199609361 Taguchi Hiroyasu Armarego Wilfred L F 1998 Glyceryl Ether Monooxygenase EC 1 14 16 5 A Microsomal Enzyme of Ether Lipid Metabolism Medicinal Research Reviews 18 1 43 89 doi 10 1002 SICI 1098 1128 199801 18 1 lt 43 AID MED3 gt 3 0 CO 2 S PMID 9436181 S2CID 432376 Umehara M Cao M Akiyama K Akatsu T Seto Y Hanada A et al June 2015 Structural Requirements of Strigolactones for Shoot Branching Inhibition in Rice and Arabidopsis Plant amp Cell Physiology 56 6 1059 72 doi 10 1093 pcp pcv028 PMID 25713176 Retrieved from https en wikipedia org w index php title Enol ether amp oldid 1222826906, wikipedia, wiki, book, books, library,

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