Chapter 14 Ethers, Epoxides, and Sulfides

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

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

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What is an ether?

• Formula
• Symmetrical or unsymmetrical
• Examples

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IUPAC Names

• Alkoxy alkane
• Priority is
• Examples

2-methyl-2-methoxypropane
Methoxycyclohexane
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Practice Problems
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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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Cyclic Ethers

• Heterocyclic oxygen is in ring.

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Structure and Polarity

• Molecular geometry
• Hybridization of Oxygen is
• Bond angle of

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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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Boiling Points
Similar to alkanes of comparable molecular weight.
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Solvent Properties

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

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Ether Complexes

• Grignard reagents
• Electrophiles
• Crown ethers

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Spectroscopy of Ethers

• IR
• Stretches Present
• Stretches Absent
• MS

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Williamson Synthesis

• Alkoxide ion 1? alkyl bromide (or tosylate)
• Example

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Phenyl Ethers

• Phenoxide ions are easily produced for use in the
  Williamson synthesis.
• Phenyl halides or tosylates cannot be used as the
  electrophile 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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Bimolecular Dehydration of Alcohols

• Industrial method, not good lab synthesis.
• If temperature is too high, alkene forms.

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Cleavage of Ethersby Hydrohalic Acids

• Reactivity
• Base
• Acid
• Alcohol leaving group is replaced by a halide.
• Reactivity gt gtgt

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Mechanism for Cleavage

• Ether is protonated.

• Alcohol leaves as halide attacks.

• Alcohol is protonated, halide attacks, and
  another molecule of alkyl bromide is formed.
  

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Phenyl Ether Cleavage

• Phenol cannot react further to become halide.
• Example

Only Products
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Autoxidation of Ethers

• The presence of atmospheric oxygen, causes ethers
  too...
• Example
• Characteristic of products
• Precautions

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What are Sulfides (Thioethers)?

• Formula
• Naming
• Example

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Thiols and Thiolates

• Acidity of thiols

• Reactivity of thiolates

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Sulfide Reactions

• Sulfides are easily oxidized to sulfoxides and
  sulfones.

• Sulfides react with unhindered alkyl halides
• to give sulfonium salts.

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What are epoxides (oxiranes)?

• Formula
• Reactivity
• Naming

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Naming Epoxides
2 Epoxy attachment to parent compound,

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Synthesis of Epoxides I

• Peroxyacid epoxidation
• Conditions
• Stereochemistry

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Synthesis of Epoxides II

• Cyclization of Halohydrin
• Variation of Williamson ether synthesis
• Reagents

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Ring Opening in Acid I

• Aqueous Acidic solution

• Alcoholic Acidic solution

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Ring Opening in Acid II

• Hydrohalic Acid solution
• Reagent
• Use

• If the epoxide is assymentically substituted,
  the more electropositive carbon in the cyclic
  ether ring will be attacked.

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Biosynthesis of Steroids
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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

• With aqueous hydroxide, a trans 1,2-diol is
  formed.
• With alkoxide in alcohol, a trans 1,2-alkoxy
  alcohol is formed.
• These are the same products that were formed in
  acid.
• Different products are formed in acid and base if
  epoxide is unsymmetrical.

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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.
• Example

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Epoxy Resins

• Polymer of bisphenol A and epichlorohydrin

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End of Chapter 14