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Ethers and Epoxides
1435-1436
2014-2015
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Ethers and Epoxides
Learning Objectives
Chapter seven discusses the following topics and by the end of this chapter the
students will:
 Know the structure of ethers
 Know the different methods of naming ethers
 Know the physical properties of ethers
 Know the different methods used in preparation of ethers
Know the reactions of opened ethers with HX
 Know the different methods used in synthesis of epoxides
Know the reactions of epoxides with different nucleophiles such as H2O, ROH,
HX, Grignard and organolithium eagents
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Ethers and Epoxides
Structure Of Ethers
Ether: is a class of organic compounds in which an oxygen atom connected to
two organic groups (alkyl or aryl"benzene ring") by σ bonds. thus Ethers are
compounds of general formula R–O–R or Ar–O–Ar or Ar–O–R
H
O
water
H
R
O
H
alcohol
R
O
R
ether
Nomenclature Of Ethers
Common names
The common names of ethers are derived by naming the alkyl groups bonded to
the oxygen then listing them in alphabetical order followed by the word "ether".
IUPAC names
The ether functional group does not have a characteristic IUPAC nomenclature
suffix, so it is necessary to designate the smaller alkyl group as an alkoxy
substituent of a parent compound (alkane , or alkene, or alkyne,or alcohol,----)
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Ethers and Epoxides
The common alkoxy substituents are given names derived from their
alkyl component
Alkyl group
Name
Alkoxy
Group Name
CH3–
Methyl
CH3O–
Methoxy
CH3CH2–
Ethyl
CH3CH2O–
Ethoxy
(CH3)2CH–
Isopropyl
(CH3)2CHO–
Isopropoxy
(CH3)3C–
tert-Butyl
(CH3)3CO–
tert-Butoxy
C6H5–
Phenyl
C6H5O–
Phenoxy
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Ethers and Epoxides
O
H3C
O
CH3
O
O
Common
Dimethyl ether
Diethyl ether
IUPAC
Methoxy methane
Ethoxy ethane
Divinyl ether
Diphenyl ether
Phenoxy benzene
O
H3C
O
C6H13
Common Hexyl methyl ether
IUPAC
Methoxy hexane
O
O
Ethyl methyl ether Ethyl vinyl ether Methyl Phenyl ether
(anisole)
Methoxy ethane
Ethoxy ethene
Methoxy benzene
CH3
CH3
CH3
IUPAC 3-Methoxyhexane
O
O
O
H3C
CH3
H3C
5-Ethoxy-2-heptene
CH3
Propenyloxy benzene5
CH3
Ethers and Epoxides
Physical Properties of Ether
1) Boiling Points
The boiling points of ethers are lower than those of alcohols having the same molecular
weights.
compound
Formula
MW
Bp (°C)
CH3-CH2-OH
46
78
Dimethyl ether
CH3-O-CH3
46
-25
propane
CH3-CH2-CH3
44
-42
ethanol
2) Solubility in water
Ethers are much less soluble in water than alcohols (Because they don’t have –OH
group, So they are not hydrogen bond donors).
More water-soluble than hydrocarbons of similar molecular weight (Because they are
polar).
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Ethers and Epoxides
Preparation of Ethers
1) Dehydration of alcohols: (only Symmetric ether)
The dehydration of alcohols takes place in the presence of acid
catalysts (H2SO4, H3PO4) under controlled temperature. The general
reaction for ether formation is
H
R O H + H O R
+
R O R
heat
Examples
2 H3C
O H
H
+
H2O
symmetric ether
+
H3C
heat
methyl alcohol
O CH3 +
H2O
methyl ether
(100 %)
2 CH3CH2
O H
H
+
CH3CH2
O CH2CH3
+
H2O
heat
ethyl alcohol
ethyl ether
(88 %)
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Ethers and Epoxides
Preparation of Ethers
2)The Williamson synthes
This method is usually used for preparation of unsymmetrical ethers
R
.. .
.
O
..
Na
+
R
+
Na
+
+
sodium phenoxide
OH NaOH
R
R
+
NaX
ether
alkyl halide
sodium alkoxide
.. .
O
...
R O
X
O
X
alkyl halide
R
+
NaX
ether
ONa
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Ethers and Epoxides
3)Alkoxide from alcohol
The alkoxide is commonly made by adding Na or K to the alcohol
The phenoxide is commonly made by adding NaOH to the phenol
Examples
+
O Na
OH
Na
OCH2CH3
CH3CH2
Br
+
sodium
cyclohexanol
NaBr
ethoxycyclohexane
cyclohexyloxide
OH
OCH3
1) Na
2) CH3I
3,3-dimethyl-2-pentanol
2-Methoxy-3,3-dimethylpentane
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Ethers and Epoxides
Reactions Of Ethers
Cleavage of ethers by hot concentrated acids
Ethers are quite stable compounds. Ethers react only under strongly
acidic condition.When ethers are heated in concentrated acid
solutions, the ether linkage is broken
General equation:
R O R
+
heat
H
X
R OH
+
R
X
(concentrated)
Specific example
CH3CH2 O CH2CH3
+
heat
H
I
CH3CH2OH + CH3CH2I
(concentrated)
The acids most often used in this reaction are HI, HBr, and HCl
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Ethers and Epoxides
If an excess of acid is present, the alcohol initially produced
is converted to alkyl halide thus the net products will be 2 moles of alkyl
halide.
R O R
2 R X
+ 2H X
+
H2O
For example
heat
CH3CH2 O CH2CH3
+
2HBr
2 CH3CH2Br + H2O
(conc, excess)
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Ethers and Epoxides
Cyclic Ethers-Epoxides:
In cyclic ethers (heterocyclic), one or more carbons are replaced with
oxygen.
O
O
O
Tetrahydrofuran
O
O
Furan
1,4-Dioxane
Oxirane
Ethylene Oxide (epoxide)
Epoxides are cyclic ethers in which the ether oxygen is part of a threemembered ring.
The simplest and most important epoxide is ethylene oxide.
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Ethers and Epoxides
Peroxyacid Epoxidation
Peroxyacids (sometimes called peracids) are used to convert alkenes to epoxides. If the
reaction takes place in aqueous acid, the epoxide opens to a glycol. Because of its
desirable solubility properties, meta-chloroperoxybenzoic acid (MCPBA) is often used
for these epoxidations.
O
+
O
R-C-O-O-H
Example
O
+
R-C-O-H
MCPBA
O
CH2Cl2
cyclohexene
Cl
MCPBA :
epoxycyclohexane
O
C-O-O-H
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Ethers and Epoxides
Epoxides are much more reactive than common dialkyl ether, because
of the strain in the three-membered ring, which is relieved when the
epoxide ring is opened after a reaction has taken place.
Examples of ring-opening reactions(cleavage carbon-oxygen bond) of
ethylene oxide that form commercially important products are:
1- Acid –Catalyzed ring opening of epoxides in water to form
glycols.
OH
O
R
CH
H3 O
CH
R
+
R
CH
CH
R
OH
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Ethers and Epoxides
2- Acid –Catalyzed ring opening of epoxides in alcohol to form alkoxy
alcohols
..
H3C
OH
O
+
R
CH
CH
R
OCH3
+
H3O
R
CH
CH
R
OH
3- Acid –Catalyzed ring opening of epoxides with a hydrohalic acid
(HCl, HBr, or HI), a halide ion attacks the protonated epoxide to give
halo alcohol .
X
O
H
X
+
R
CH
CH
R
R
CH
CH
R
OH
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Ethers and Epoxides
4- Ring opening of epoxides with Grignard and Organolithium
Reagents to give longer alcohols
OH
O
R'
MgX
+
R
CH
1) ether
CH
R
R
CH
CH
R
2) H3O+
or R'
R'
Li
5- Ring opening of epoxides with amines
NHCH3
O
CH3NH2
+
R
CH
CH
R
H3O+
R
CH
CH
R
OH
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Ethers and Epoxides
Exercise 1
Give a correct name for each of the following compounds.
H3C O CH2CH2CH3
CH3CHCH2CH3
CH2 O CH2CH3
CH2=CHCH2 O CH2CH=CH2
O CH3
O
CH3CH2CHCH=CH2
CH3
O CH3
O CH2CH3
Exercice 2
Propose a Williamson synthesis of 3-butoxy-1,1-dimethylcyclohexane
from 3,3-dimethylcyclohexanol and butanol
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Ethers and Epoxides
Exercise 3
Predict the products of the following reactions.
(a) Di-n-butyl ether
conc, HBr
CH3MgBr
(e)
O
heat
CH3OH
(b)
CH3O
(f)
O
O
HBr
(c)
CH2Cl2
H3O+
LiAlH4
(e)
O
CH3OH
MCPA
(g)
O
(d)
H2O
O
H2O
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Ethers and Epoxides
Thank You for your kind attention !
Questions?
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