Chapter 14
Ethers,Epoxides,
and Sulfides
Jo Blackburn
Richland College,Dallas,TX
Dallas County Community College District
2003,Prentice Hall
Organic Chemistry,5th Edition
L,G,Wade,Jr.
Chapter 14 2
Introduction
Formula R-O-R where R is alkyl or aryl.
Symmetrical or unsymmetrical
Examples:
O C H 3
C H 3 O C H 3 O
=>
Chapter 14 3
Structure and Polarity
Bent molecular geometry
Oxygen is sp3 hybridized
Tetrahedral angle
=>
Chapter 14 4
Boiling Points
Similar to alkanes of comparable molecular weight.
Chapter 14 5
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,
=>
Chapter 14 6
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,=>
Chapter 14 7
Ether Complexes
Grignard reagents
Electrophiles
Crown ethers
O B
H
H
H
+
_
B H 3 T H F
=>
Chapter 14 8
Common Names of Ethers
Alkyl alkyl ether
Current rule,alphabetical order
Old rule,order of increasing complexity
Symmetrical,use dialkyl,or just alkyl.
Examples:
C H 3 C H 2 O C H 2 C H 3
diethyl ether or
ethyl ether
C H 3 O C
C H 3
C H 3
C H 3
t-butyl methyl ether or
methyl t-butyl ether =>
Chapter 14 9
IUPAC Names
Alkoxy alkane
Examples:
C H 3 O C
C H 3
C H 3
C H 3
2-methyl-2-methoxypropane
O C H 3
Methoxycyclohexane
=>
Chapter 14 10
Cyclic Ethers
Heterocyclic,oxygen is in ring.
Epoxides (oxiranes)
H 2 C C H 2
O
Oxetanes O
Furans (Oxolanes )
O O
Pyrans (Oxanes )
O O
Dioxanes
O
O
=>
Chapter 14 11
Naming Epoxides
Epoxy attachment to parent compound,
1,2-epoxy-cyclohexane
Alkene oxide,from usual synthesis method
p e r o x y b e n z o i c a c i d
O
H
H
cyclohexene oxide
Oxirane as parent,oxygen number 1
trans-2-ethyl-3-methyloxiraneOH
H
C H 3
C H 3 C H 2
=>
Chapter 14 12
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,
=>
Chapter 14 13
Williamson Synthesis
Alkoxide ion + 1? alkyl bromide (or tosylate)
Example:
C H 3 O H
C H 3
C H 3
+ K C H 3 O
C H 3
C H 3
_
K
+
C H 3 O
C H 3
C H 3
_
+ C H 3 C H 2 C
H
H
B r C H 3 O
C H 3
C H 3
C H 2 C H 2 C H 3 + B r
_
=>
Chapter 14 14
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 H
+ N a O H
O
_
N a +
+ H O H
=>
Chapter 14 15
Alkoxymercuration-
Demercuration
Use mercuric acetate with an alcohol to
add RO-H to a double bond and form
the Markovnikov product.
C H 3 C H 2 C H C H 2
1) H g ( O A c ) 2,C H 3 O H
2) N a B H 4
C H 3 C H 2 C H C H 2
H
O C H 3
=>
Chapter 14 16
Bimolecular Dehydration
of Alcohols
Industrial method,not good lab synthesis.
If temperature is too high,alkene forms.
=>
H O C H 2 C H 3C H 3 C H 2 O H C H 3 C H 2 O C H 2 C H 3+ H 2 S O 4
140° C
Chapter 14 17
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
=>
Chapter 14 18
Mechanism for Cleavage
C H 3 O C H 3 H B r C H 3 O C H 3
H
_B r
_
++
B r
_ +
C H 3 O C H 3
H
B r C H 3 + H O C H 3
Ether is protonated.
Alcohol leaves as halide attacks.
Alcohol is protonated,halide attacks,
and another molecule of alkyl bromide is
formed,=>
Chapter 14 19
Phenyl Ether Cleavage
Phenol cannot react further to become
halide.
Example:
O C H 2 C H 3
H B r
O H
+ C H 3 C H 2 B r
=>
Chapter 14 20
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,
=>
Chapter 14 21
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.
Example:
S C H 3
methyl phenyl sulfide
or
methylthiobenzene =>
Chapter 14 22
Thiols and Thiolates
R-SH about same acidity as phenols.
C H 3 C H 2 S H + N a O H N a + + H O HC H 3 C H 2 S _
Thiolates are better nucleophiles,weaker
bases,than alkoxides.
C H 3 C C H 3
H
B r
C H 3 O H
C H 3 S
_
C H 3 C C H 3
H
S C H 3
2? halide Substitution product =>
Chapter 14 23
Sulfide Reactions
Sulfides are easily oxidized to sulfoxides
and sulfones.
Sulfides react with unhindered alkyl halides
to give sulfonium salts.
+C H 3 S C H 3 C H 3 I C H 3 S C H 3
C H 3
+
I
_
=>
Chapter 14 24
Synthesis of Epoxides
Peroxyacid epoxidation
Cyclization of Halohydrin
HH
H 2 O,C l 2
C lH
H O H O H
_
C lH
O H_
H H
O
=>
Chapter 14 25
Ring Opening in Acid
Trans diol formed in water solvent.
Alkoxy alcohol formed in alcohol solvent.
1,2-Dihalide formed with HI or HBr,=>
H
O
H
H
+
,H 2 O
H
H O H
O H
H
O
H
H +,C H 3 O H
H
H O H
O C H 3
Chapter 14 26
Biosynthesis of Steroids
=>
Chapter 14 27
Ring Opening in Base
Epoxide’s high ring strain makes it
susceptible to nucleophilic attack.
=>
Chapter 14 28
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,=>
Chapter 14 29
Orientation of
Epoxide Opening
Base attacks the least hindered carbon.
In acid,the nucleophile attacks the protonated
epoxide at the most substituted carbon.
C H 3 C H 2 O H
H C C H 2
C H 3
O H
O C H 2 C H 3
_
H C C H 2
C H 3
O
O C H 2 C H 3O C H
2 C H 3
H C C H 2
C H 3
O
=>
H C C H 2
O HH
3 C
O C H 2 C H 3
+
H C C H 2
O HH
3 C
O C H 2 C H 3H
C H 3 C H 2 O H
+
H C C H 2
C H 3
O
H
Chapter 14 30
Reaction with
Grignard and R-Li
Strong base opens the epoxide ring by
attacking the less hindered carbon.
Example:
H 2 C C H C H 3
O
+
M g B r
1 ) e t h e r
2) H 3 O
+
C H 2 C H C H 3
O H
=>
Chapter 14 31
Epoxy Resins
Polymer of bisphenol A and epichlorohydrin
H O C
C H 3
C H 3
O H
b is p h e n o l A
H 2 C C H C H 2 C l
O
e p ic h l o r o h y d r in
=>
Chapter 14 32
End of Chapter 14