24'11 Preparation of Aryl Ethers

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24.11Preparation of Aryl Ethers
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Typical Preparation is by Williamson Synthesis
SN2


RX
NaX
3
Example
acetone

CH3I
heat
(95)
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Example

K2CO3
acetone, heat
(86)
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Aryl Ethers from Aryl Halides
CH3OH


KOCH3
KF
25C
(93)

• nucleophilic aromatic substitution is effective
  with nitro-substituted (ortho and/or para) aryl
  halides

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24.12Cleavage of Aryl Ethersby Hydrogen Halides
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Cleavage of Alkyl Aryl Ethers
Ar

O
R

• An alkyl halide is formed never an aryl halide!

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Example
HBr

CH3Br
heat
(85-87)
(57-72)
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24.13Claisen Rearrangementof Allyl Aryl Ethers
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Allyl Aryl Ethers Rearrange on Heating

• allyl group migrates to ortho position

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Mechanism
rewrite as
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Sigmatropic Rearrangement
Claisen rearrangement is an example of a
sigmatropic rearrangement. A ? bond
migratesfrom one end of a conjugated ? electron
systemto the other.
conjugated ? electron system is the allyl group
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24.14Oxidation of PhenolsQuinones
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Quinones

• The most common examples of phenol oxidationsare
  the oxidations of 1,2- and 1,4-benzenediolsto
  give quinones.

(76-81)
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Quinones

• The most common examples of phenol oxidationsare
  the oxidations of 1,2- and 1,4-benzenediolsto
  give quinones.

O
O
Ag2O
diethyl ether
(68)
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Some quinones are dyes
Alizarin(red pigment)
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Some quinones are important biomolecules
Ubiquinone (Coenzyme Q) n 6-10 involved in
biological electron transport
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Some quinones are important biomolecules
Vitamin K (blood-clotting factor)