Transcript Ethers, Epoxides, and Sulfides

CHE 242
Unit V
Structure and Reactions of
Alcohols, Ethers and
Epoxides; Basic Principles of
NMR Spectroscopy
CHAPTER FOURTEEN
Terrence P. Sherlock
Burlington County College
2004
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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3
=>
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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=>
4
Ether Complexes
• Grignard reagents
• Electrophiles
H
_
+
O B H
H
BH3 THF
• Crown ethers
=>
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5
Common Names of Ethers
•
•
•
•
•
Alkyl alkyl ether
Current rule: alphabetical order
Old rule: order of increasing complexity
Symmetrical: use dialkyl, or just alkyl.
CH3
Examples:
CH3CH2
CH3
O CH2CH3
O C
CH3
CH3
diethyl ether or
ethyl ether
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t-butyl methyl ether or
methyl t-butyl ether 6 =>
IUPAC Names
• Alkoxy alkane
• Examples:
CH3
CH3
O C
O CH3
CH3
CH3
2-methyl-2-methoxypropane
Methoxycyclohexane
=>
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Naming Epoxides
• Alkene oxide, from usual synthesis method
H
peroxybenzoic acid
O
cyclohexene oxide
H
• Epoxy attachment to parent compound,
1,2-epoxy-cyclohexane
• Oxirane as parent, oxygen number 1
H
CH3CH2
O
CH3
H
trans-2-ethyl-3-methyloxirane
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8
Spectroscopy of Ethers
• IR: Compound contains oxygen, but
O-H and C=O stretches are absent.
• MS: -cleavage to form oxonium ion, or
loss of either alkyl group.
• NMR: 13C-O signal between 65-90,
1H-C-O signal between 3.5-4.
=>
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Williamson Synthesis
• Alkoxide ion + 1 alkyl bromide (or tosylate)
• Example:
CH3
CH3
O H
+
K
CH3
CH3
CH3
CH3
_
O
+ CH3CH2
CH3
CH3
H
C
CH3
_ +
O K
CH3
Br
CH3
H
_
O CH2CH2CH3 + Br
CH3
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10
Phenyl Ethers
• Phenoxide ions are easily produced for
use in the Williamson synthesis.
• Phenyl halides or tosylates cannot be
used in this synthesis method.
_
O Na+
O H
+ NaOH
+
HOH
=>
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Bimolecular Dehydration
of Alcohols
• Industrial method, not good lab synthesis.
• If temperature is too high, alkene forms.
CH3CH2
O H + H O CH2CH3
H2SO4
CH3CH2 O CH2CH3
140°C
=>
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Cleavage of Ethers
• Ethers are unreactive toward base, but
protonated ethers can undergo
substitution reactions with strong acids.
• Alcohol leaving group is replaced by a
halide.
• Reactivity: HI > HBr >> HCl
=>
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Mechanism for Cleavage
• Ether is protonated.
CH3
O CH3
H Br
CH3
H
+
O CH3
_
_
+ Br
• Alcohol leaves as halide attacks.
_
Br
CH3
H
+
O CH3
Br CH3 + H O CH3
• 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:
OH
O CH2CH3
HBr
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+ CH3CH2
Br
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15
Autoxidation of Ethers
• In the presence of atmospheric oxygen,
ethers slowly oxidize to hydroperoxides
and dialkyl peroxides.
• Both are highly explosive.
• Precautions:
Do not distill to dryness.
Store in full bottles with tight caps.
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POWER POINT IMAGES FROM
“ORGANIC CHEMISTRY, 5TH EDITION”
L.G. WADE
ALL MATERIALS USED WITH PERMISSION OF AUTHOR
PRESENTATION ADAPTED FOR BURLINGTON COUNTY COLLEGE
ORGANIC CHEMISTRY COURSE
BY:
ANNALICIA POEHLER STEFANIE LAYMAN
CALY MARTIN
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