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Chapter 18
Ethers and Epoxides;
Thiols and Sulfides
Ethers

Definition: Two organic groups bonded to the
same oxygen atom
O
R

R'
Examples:
CH3CH2 O CH2CH3
Diethyl ether
O
CH3
Methyl phenyl ether (Anisole)
O
Tetrahydrofuran (cyclic ether)
Naming of Ethers
There are two ways to name it:

Identifying the two organic substituents and
adding the word ether
O
CH3
CH3
Dimethyl ether
H3C
CH3
O
C
H3C
O
Tert-Butyl methyl ether
CH3
CH2CH3
Ethyl-phenyl ether

If other functional groups are present, the ether
part is considered an alkoxy substituent.
O
Tert-butoxy butane
O
OCH3
Para-ethoxy methoxy benzene
OCH3
1-methoxy-cyclohexene
CH3
4-tert-Butoxy-1-cyclohexene
O C
CH3
CH3
O
p-dimethoxybenzene
Isopropoxy cyclohexane
CH3O
OCH3

Physical Properties
1.
Soluble in water
Boiling point: very low, about 200C
R—O—R bonds: tetrahedral bond angle
The Oxygen atom is sp3-hybridized
2.
3.
4.
Preparation of Ethers
Symmetrical ethers
R-O-R
R OH
+
R OH
+
H
R O R
+
H2O
Mechanism:
R
R
H2SO4
O
+
O
H
H
H
R
O
H
H
R
O+ R
H
O
H
R
O
R
Examples
H
CH3CH2
O
H
+ CH3CH2
O
SN2
CH3CH2
O CH2CH3
Symmetrical ethers
R-O-R’

The Williamson Ether Synthesis:
NaH
+
R O Na
R O H
+
R O Na
+
R'
X
+
H2
R O R'
+
X
-
Examples
CH2OH
O
HO
HO
HO OH
α-D-Glucose
CH3 I
Ag2O
CH3O
CH3O
CH2OCH3
O
+
CH3O
AgI
OCH3
Α-D-Glucose pentamethyl ether
CH3
H3C
C
- +
O Na
SN2
+
H3C
I
CH3
tert-Butoxide ion
CH3
H3C
C
O CH3
CH3
Iodomethane
tert-Butyl methyl ether
H
CH3O
-
Na
+
+
H2C
Methoxide ion
CH3
C
E2
Cl
CH3
2-Chloro-2-methylpropane
CH3
H2C
+
C
CH3
2-Methylpropene
CH3OH
+
Cl

Alkoxymercuration of Alkenes
1) Reaction
1. (CF3CO2)2Hg, CH3CH2OH
2. NaBH4
OCH2CH3
2. Mechanism
+
OOCCF3
Hg
Hg OOCCF3
OOCCF3
OCH2CH3
H
Hg OOCCF3
OCH2CH3
H
Hg OOCCF3
OOCCF3
Hg OOCCF3
OCH2CH3
OCH2CH3
H
NaBH4
OCH2CH3
3. Examples
H
H
C
H
C
H
(CF3CO2)2Hg,
OCH3
C
HgO2CCF3
C
CH3OH
H
H
Styrene
H
NaBH4
OCH3
C
H
C
H
H
1-Methoxy-1-phenyethane
Reaction of Ethers

Acidic Cleavage
1) Ethers with primary and secondary alkyl
groups react by an SN2
CH3CH O CH2CH3
CH3
Ethyl isopropyl ether
HI, H2O
CH3CH O H
+
CH3CH2
I
CH3
Isopropyl alcohol
Iodoethane
Mechanism
More hindered
H
Less hindered
I
H
CH3CH O CH2CH3
CH3
CH3CH O CH2CH3
I
CH3
SN2
CH3CH O H
CH3
+
-
CH3CH2
I
Examples:
O
OH
HBr, H2O
CH2CH3
+
Reflux
Ethyl phenyl ether
Bromoethane
Phenol
OH
OCH2CH3
CH3CHCOOH
CH3CH2 Br
+
2-Ethoxypropanoic acid
HI
100OC
H2O
CH3CH2 I
Iodoethane
+
CH3CHCOOH
Lactic acid
2) Ethers with a tertiary, benzylic, or allylic
group react by an SN1 or E1
E1 reaction
CH3
O
C
H3C
CH3
tert-Butyl cyclohexyl ether
CF3CO2H,
H3C
OH
E1
+
OOC
C
CH2
H3C
Cyclohexanol
2-Methylpropene
Mechanism:
CH3
O
CH3
C
H3C
H3C
CH3
OH
C+
O
H OOCCF3
+
CH3
H
H3C
+
C
+
H3C
CH2
OOCCF3
H3C
OH
+
C
H3C
CH2
SN1 reaction
CH3
CH3
CH3C
CH3
HBr
O CH2CH2CH3
CH3C
CH3
Br
+
H OCH2CH2CH3
Mechanism:
CH3
CH3
CH3C
CH3
O CH2CH2CH3
CH3C
+
+
CH3CH2CH2 O
H
Br
CH3
H OCH2CH2CH3
+
CH3
+
CH3C
CH3
CH3
CH3C
CH3
Br
+
H OCH2CH2CH3
Br
-

Claisen Rearrangement
1) Claisen rearrangement is pecific to allyl aryl ethers, Ar-O-CH2CH=CH2
2) Example:
Na+ O
OH
+
NaH
Phenol
THF
BrCH2CH=CH2
solution
Sodium phenoxide
CH2
O
OCH2CH=CH2
CH
CH2
Allyl phenyl ether
Allyl phenyl ether
OH
Claisen rearrangement
CH2CH=CH2
250oC
0-Allylphenol
3) Mechanism:
CH2
O
CH
O
H2 C
CH2
CH2
CH2
H2C
O
CH
CH2
H
Transition state
OH
CH2CH=CH2