Ethers &
Epoxides
Unit 12
12-1
Structure
 The
functional group of an ether is an oxygen
atom bonded to two carbon atoms
• in dialkyl ethers, oxygen is sp3 hybridized with bond
angles of approximately 109.5°.
• in dimethyl ether, the C-O-C bond angle is 110.3°
H
H
••
H
C
H
O
••
C
H
H
12-2
Structure
• in other ethers, the ether oxygen is bonded to an sp2
hybridized carbon
• in ethyl vinyl ether, for example, the ether oxygen is
bonded to one sp3 hybridized carbon and one sp2
hybridized carbon
Ethoxyethene
CH3 CH2 -O-CH=CH2
(Ethyl vinyl ether)
12-3
Nomenclature: ethers
 IUPAC: the longest carbon chain is the parent
• name the OR group as an alkoxy substituent

Common names: name the groups bonded to oxygen in
alphabetical order followed by the word ether
OH
CH3 OCCH3
CH3 CH2 OCH 2 CH3
OCH2 CH3
Ethoxyethane
(Diethyl ether)
CH3
trans-2-Ethoxycyclohexanol
CH3
2-Methoxy-2methylpropane
(tert-Butyl methyl ether)
12-4
Nomenclature: ethers
 Although
cyclic ethers have IUPAC names, their
common names are more widely used
• IUPAC: prefix ox- shows oxygen in the ring
• the suffixes -irane, -etane, -olane, and -ane show three,
four, five, and six atoms in a saturated ring
2
O
3
1O
O
O
O
O
Oxirane
Oxetan e
Oxolane
Oxan e
1,4-D ioxane
(Ethylene oxid e)
(Tetrahydrofuran) (Tetrahydropyran)
12-5
Physical Properties
 Although
ethers are polar compounds, only weak
dipole-dipole attractive forces exist between their
molecules in the pure liquid state
12-6
Physical Properties
 Boiling
points of ethers are
• lower than alcohols of comparable MW
• close to those of hydrocarbons of comparable MW
 Ethers
are hydrogen bond acceptors
• they are more soluble in H2O than are hydrocarbons
12-7
Preparation of Ethers
 Acid-catalyzed
dehydration of alcohols
• diethyl ether and several other ethers are made on an
industrial scale this way
• a specific example of an SN2 reaction in which a poor
leaving group (OH-) is converted to a better one (H2O)
2CH3 CH2 OH
Ethanol
H2 SO4
140°C
CH3 CH2 OCH2 CH3 + H2 O
Diethyl ether
12-8
Epoxides
 Epoxide:
a cyclic ether in which oxygen is one
atom of a three-membered ring
• simple epoxides are named as derivatives of oxirane
• where the epoxide is part of another ring system, it is
shown by the prefix epoxy• common names are derived from the name of the
alkene from which the epoxide is formally derived
2
H2 C
3
CH 2
1O
Oxirane
(Ethylene oxide)
H3 C
H
H
C
C
CH 3
O
cis-2,3-Dimethyloxirane
(cis-2-Butene oxide)
1
H
O
2
H
1,2-Epoxycyclohexane
(Cyclohexene oxide)
12-9
Synthesis of Epoxides
 Ethylene
oxide, one of the few epoxides
manufactured on an industrial scale, is prepared
by air oxidation of ethylene
2 CH2 = CH2 + O2
Ag
2 H2 C
CH2
O
Oxirane
(Ethylene oxide)
12-10
Synthesis of Epoxides
 The
most common laboratory method is
oxidation of an alkene using a peroxycarboxylic
acid (a peracid)
O
COOH
Cl
meta-chloroperoxybenzoic acid
(MCPBA)
O
COOH
CO
O
Mg
2
2+
O
CH 3 COOH
Peroxyacetic acid
(Peracetic acid)
Magnesium
monoperoxyphthalate
(MMPP)
12-11
Synthesis of Epoxides
 Epoxidation
+
Cycloh exene
of cyclohexene
O
RCOOH
H
CH2 Cl2
A p eroxycarboxylic acid
O
+
O
RCOH
H
1,2-Ep oxycyclohexan e A carboxylic
(Cycloh exene oxide)
acid
12-12
Synthesis of Epoxides
 Epoxidation
is stereospecific:
• epoxidation of cis-2-butene gives only cis-2,3dimethyloxirane
• epoxidation of trans-2-butene gives only trans-2,3dimethyloxirane
H
CH3
C
H3 C
RCO3 H
C
H
trans-2-Buten e
H
H3 C
C
C
CH3
H
O
+
H
H3 C
C
O
t rans-2,3-D imethyloxirane
(a racemic mixture)
C
H
CH3
12-13
Reactions of Epoxides
 Acid-catalyzed
ring opening
• in the presence of an acid catalyst, such as sulfuric
acid, epoxides are hydrolyzed to glycols
O + H2 O
Oxirane
(Ethylene oxide)
H+
HO
OH
1,2-Ethanediol
(Ethylene glycol)
12-14
Crown Ethers
 Crown
ether: a cyclic polyether
derived from ethylene glycol or a
substituted ethylene glycol
• the parent name is crown, preceded by
a number describing the size of the
ring and followed by the number of
oxygen atoms in the ring
O
O
O
O
O
O
18-Crown-6
12-15
Crown Ethers
 The
diameter of the cavity
created by the repeating
oxygen atoms is comparable
to the diameter of alkali
metal cations
• 18-crown-6 provides very
effective solvation for K+
12-16
Thioethers
 The
sulfur analog of an ether
• IUPAC name: select the longest carbon chain as the
parent and name the sulfur-containing substituent as
an alkylsulfanyl group
• common name: list the groups bonded to sulfur
followed by the word sulfide
S
Ethylsulfanylethan e
(D ieth yl s ulfide)
S
2-Eth yls ulfanylprop ane
(Eth yl is op ropyl su lfid e)
12-17
Nomenclature
 Disulfide:
contains an -S-S- group
• IUPAC name: select the longest carbon chain as the
parent and name the disulfide-containing substituent
as an alkyldisulfanyl group
• Common name: list the groups bonded to sulfur and
add the word disulfide
S
S
Ethyldis ulfanylethane
(D ieth yl d isulfide)
12-18