Chapter 14 Ethers, Epoxides, and Sulfides

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Chapter 14 Ethers, Epoxides, and Sulfides
Organic Chemistry, 5th EditionL. G. Wade, Jr.

• Modified from Jo Blackburn
• Richland College, Dallas, TX
• Dallas County Community College District
• ã 2003, Prentice Hall

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Introduction

• Formula R-O-R where R is alkyl or aryl.
• Symmetrical or unsymmetrical
• Examples

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Structure and Polarity

• Bent molecular geometry water like
• Oxygen is sp3 hybridized
• Tetrahedral angle

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Boiling Points
Similar to alkanes of comparable molecular weight.
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Hydrogen Bond Acceptor

• Ethers cannot H-bond to each other.
• In the presence of -OH or -NH (donor), the lone
  pair of electrons from ether forms a hydrogen
  bond with the -OH or -NH.

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Solvent Properties

• Nonpolar solutes dissolve better in ether than in
  alcohol.
• Ether has a large dipole moment, so polar solutes
  also dissolve.
• Ethers solvate cations.
• Ethers do not react with strong bases like the
  alcohol H does.

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Ether Complexes

• Grignard reagents
• Ether is necessary
• Electrophiles

• Crown ethers

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Common Names of Ethers

• Alkyl alkyl ether
• Current rule alphabetical order
• Old rule order of increasing complexity
• Symmetrical use dialkyl, or just alkyl.
• Examples

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IUPAC Names

• Alkoxy alkane use the more complex alkyl group
  as the root.

t-butyl methyl ether or methyl t-butyl ether
2-methyl-2-methoxypropane
Methoxycyclohexane
gt
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Cyclic Ethers

• Heterocyclic noncarbon in the ring oxygen is in
  ring.

(4 member ring)
(2 oxygen in 6 member ring)
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Williamson Synthesis

• Alkoxide ion 1? alkyl bromide (or tosylate)
• (1) form alkoxide (2) SN2 attack of R-X

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Phenyl Ethers

• Phenoxide ions are easily produced for use in the
  Williamson synthesis.
• Phenyl halides or tosylates cannot be used in
  this synthesis method.

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Alkoxymercuration-Demercuration

• Use mercuric acetate with an alcohol to add RO-H
  to a double bond and form the Markovnikov product.

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• Industrial method, not good lab synthesis.
• Symmetrical Ethers
• Need unhindered primary alcohol.
• If temperature is too high or steric hindrance,
  elimination is favored and alkene forms.

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Cleavage of Ethers

• Ethers are unreactive toward base, so make good
  solvents
• Protonated ethers can undergo substitution
  reactions with strong acids.
• Alcohol leaving group is replaced by a halide.
• Reactivity HI gt HBr gtgt HCl
  gt

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Mechanism for Cleavage

• Ether is protonated.
• Alcohol leaves as halide attacks.
• Alcohol reacts with HX to give another ROH

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Sulfides (Thioethers)

• R-S-R, analog of ether
• Name like ethers, replacing sulfide for ether
  in common name, or alkylthio for alkoxy in
  IUPAC system.
• More reactive than ethers!

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Thiols and Thiolates

• R-SH about same acidity as phenols.

• Thiolates are better nucleophiles, weaker
  bases, than alkoxides.

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Epoxides

• Synthesis and Reactivity

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Naming Epoxides

• Epoxy attachment to parent compound,
• 1,2-epoxy-cyclohexane

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Synthesis of Epoxides

• Peroxyacid epoxidation

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Synthesis of Epoxides

• Cyclization of Halohydrin
• Alkoxide ion and halide in same molecule.

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Synthesis of Epoxides
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Ring Opening in Acidmore reactive than ethers
due to ring-strain

• Trans diol formed in water solvent.

• Alkoxy alcohol formed in alcohol solvent.

• 1,2-Dihalide formed with HI or HBr.

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Ring Opening in Base

• Epoxides high ring strain makes it susceptible
  to nucleophilic attack.

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Epoxide Opening in Base

• aqueous hydroxide, a trans 1,2-diol is formed.
• With alkoxide in alcohol, a trans 1,2-alkoxy
  alcohol is formed.

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Write out the Mechanism(s)
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Orientation of Epoxide Opening

• Base attacks the least hindered carbon.

• In acid, the nucleophile attacks the protonated
• epoxide at the most substituted carbon.

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Reaction with Grignard and R-Li

• Strong base opens the epoxide ring by attacking
  the less hindered carbon.

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End of Chapter 14
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For Wednesday

• 32, 34, 37, 39, 42

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