Organic Chemistry, 5th Edition
L. G. Wade, Jr.
Chapter 14
Ethers, Epoxides,
and Sulfides
Jo Blackburn
Richland College, Dallas, TX
Dallas County Community College District
2003, Prentice Hall
Introduction
• Formula R-O-R where R is alkyl or aryl.
• Symmetrical or unsymmetrical
• Examples:
CH3
O
O CH3
O CH3
=>
Chapter 14
2
Structure and Polarity
• Bent molecular geometry
• Oxygen is sp3 hybridized
• Tetrahedral angle
Chapter 14
3
=>
Boiling Points
Similar to alkanes of comparable molecular weight.
Chapter 14
4
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
5
=>
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
=>
6
Ether Complexes
• Grignard reagents
• Electrophiles
H
+ _
O B H
H
BH3 THF
• Crown ethers
=>
Chapter 14
7
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
Chapter 14
t-butyl methyl ether or
methyl t-butyl ether 8 =>
IUPAC Names
• Alkoxy alkane
• Examples:
CH3
CH3
O CH3
O C CH3
CH3
2-methyl-2-methoxypropane
Methoxycyclohexane
=>
Chapter 14
9
Cyclic Ethers
• Heterocyclic: oxygen is in ring.
• Epoxides (oxiranes)
H2C CH2
O
• Oxetanes
• Furans
O
O
• Pyrans
(Oxolanes
O
(Oxanes
O
)
)
O
O
•Dioxanes
=>
O
Chapter 14
10
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
Chapter 14
=>
11
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
12
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
Chapter 14
=>
13
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
=>
Chapter 14
14
AlkoxymercurationDemercuration
Use mercuric acetate with an alcohol to
add RO-H to a double bond and form
the Markovnikov product.
CH3CH2CH CH2
1) Hg(OAc)2, CH3OH
2) NaBH4
H
CH3CH2CH CH2
OCH3
=>
Chapter 14
15
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
=>
Chapter 14
16
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
17
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.
=>
Chapter 14
18
Phenyl Ether Cleavage
• Phenol cannot react further to become
halide.
• Example:
OH
O CH2CH3
HBr
Chapter 14
+ CH3CH2
Br
=>
19
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
20
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
CH3
methyl phenyl sulfide
or
methylthiobenzene
Chapter 14
=>
21
Thiols and Thiolates
• R-SH about same acidity as phenols.
_
CH3CH2
SH + NaOH
CH3CH2
S
+
Na
+ HOH
• Thiolates are better nucleophiles, weaker
bases, than alkoxides.
Br
CH3
C CH3
H
_
CH3S
CH3OH
2 halide
SCH3
CH3
C CH3
H
Substitution product
Chapter 14
=>
22
Sulfide Reactions
• Sulfides are easily oxidized to sulfoxides
and sulfones.
• Sulfides react with unhindered alkyl halides
to give sulfonium salts.
CH3
S
CH3
+ CH3
I
CH3
+
S
_
CH3
I
=>
CH3
Chapter 14
23
Synthesis of Epoxides
• Peroxyacid epoxidation
• Cyclization of Halohydrin
H
H2O, Cl2
H
HO
H
H
_
OH
Cl
_
O
H
O
H
Cl
H
H
=>
Chapter 14
24
Ring Opening in Acid
• Trans diol formed in water solvent.
+
H , H2O
O
H
H
H
HO
H
OH
• Alkoxy alcohol formed in alcohol solvent.
+
H , CH3OH
O
H
H
HO
H
H
OCH3
• 1,2-Dihalide formed with HI or HBr.
Chapter 14
=>
25
Biosynthesis of Steroids
=>
Chapter 14
26
Ring Opening in Base
Epoxide’s high ring strain makes it
susceptible to nucleophilic attack.
=>
Chapter 14
27
Epoxide Opening in Base
• With aqueous hydroxide, a trans 1,2-diol
is formed.
• With alkoxide in alcohol, a trans 1,2alkoxy 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
28
Orientation of
Epoxide Opening
• Base attacks the least
hindered carbon.
_
O
O
HC CH2
CH3CH2OH
HC
CH3
OCH2CH3
CH2
CH3 OCH2CH3
OH
HC CH2
CH3 OCH2CH3
• In acid, the nucleophile attacks the protonated
epoxide at the most substituted carbon.
H
O+
HC
CH3CH2OH
CH2
CH3
OH
H3C
HC CH2
2CH3
H OCH
+
Chapter 14
OH
H3C
HC CH2
OCH2CH3
=>
29
Reaction with
Grignard and R-Li
• Strong base opens the epoxide ring by
attacking the less hindered carbon.
• Example:
OH
MgBr
O
H2C CHCH3
1) ether
+
2) H3O
CH2
CHCH3
+
=>
Chapter 14
30
Epoxy Resins
Polymer of bisphenol A and epichlorohydrin
CH3
HO
C
O
OH
CH3
H2C CHCH2Cl
epichlorohydrin
bisphenol A
=>
Chapter 14
31
End of Chapter 14
Chapter 14
32