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6.18 Epoxidation of Alkenes

6.18 Epoxidation of Alkenes. CHCH 3. H 2 C. CH 2. H 2 C. O. O. Epoxides. are examples of heterocyclic compounds three-membered rings that contain oxygen ethylene oxide propylene oxide. H 3 C. CHCH 3. CHCH 3. H 2 C. C. H 3 C. O. O. Epoxide Nomenclature.

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6.18 Epoxidation of Alkenes

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  1. 6.18Epoxidation of Alkenes

  2. CHCH3 H2C CH2 H2C O O Epoxides • are examples of heterocyclic compounds • three-membered rings that contain oxygen • ethylene oxide propylene oxide

  3. H3C CHCH3 CHCH3 H2C C H3C O O Epoxide Nomenclature • Substitutive nomenclature: named as epoxy-substituted alkanes. • “epoxy” precedes name of alkane • 1,2-epoxypropane 2-methyl-2,3-epoxybutane 1 4 2 3

  4. O H H Problem 6.17 Give the IUPAC name, including stereochemistry, for disparlure. • cis-2-Methyl-7,8-epoxyoctadecane

  5. O C RCOOH C O RCOH C C O Epoxidation of Alkenes + peroxy acid +

  6. O + CH3COOH O + CH3COH O Example (52%)

  7. O C RCOOH C O RCOH C C O Stereochemistry of Epoxidation + syn addition +

  8. O H H Problem 6.18 Give the structure of the alkene,including stereochemistry, that you wouldchoose as the starting material in a preparationof synthetic disparlure.

  9. H H O H H Problem 6.18 Give the structure of the alkene,including stereochemistry, that you wouldchoose as the starting material in a preparationof synthetic disparlure. peroxy acid

  10. Relative Rates of Epoxidation • ethylene H2C=CH2 1 • propene CH3CH=CH2 22 • 2-methylpropene (CH3)2C=CH2 484 • 2-methyl-2-butene (CH3)2C=CHCH3 6526 • More highly substituted double bonds react faster.Alkyl groups on the double bond make itmore “electron rich.”

  11. Mechanism of Epoxidation

  12. 6.19Ozonolysis of Alkenes • Ozonolysis has both synthetic and analytical applications. • synthesis of aldehydes and ketones • identification of substituents on the double bond of an alkene

  13. O C C C C O O Ozonolysis of Alkenes • First step is the reaction of the alkene with ozone.The product is an ozonide. + O3

  14. O C C C C O O O C Ozonolysis of Alkenes • Second step is hydrolysis of the ozonide. Two aldehydes, two ketones, or an aldehyde and a ketone are formed. + O3 H2O, Zn + O C

  15. O C C C C O O O O C C Ozonolysis of Alkenes • As an alternative to hydrolysis, the ozonide canbe treated with dimethyl sulfide. + O3 (CH3)2S +

  16. CH2CH3 CH3 C C H CH2CH3 CH2CH3 CH3 O O C C H CH2CH3 Example 1. O3 2. H2O, Zn + (38%) (57%)

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