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Chapter 16 Ethers, Epoxides, and Sulfides

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Title: Chapter 16 Ethers, Epoxides, and Sulfides


1
Chapter 16Ethers, Epoxides, and Sulfides
Dr. Wolf's CHM 201 202
16-1
2
Nomenclature of Ethers, Epoxides, and Sulfides
Dr. Wolf's CHM 201 202
16-2
3
Substitutive IUPAC Names of Ethers
  • name as alkoxy derivatives of alkanes

Dr. Wolf's CHM 201 202
16-3
4
Functional Class IUPAC Names of Ethers
  • name the groups attached to oxygen in
    alphabetical order as separate words "ether"
    is last word

Dr. Wolf's CHM 201 202
16-4
5
Substitutive IUPAC Names of Sulfides
  • name as alkylthio derivatives of alkanes

(methylthio)cyclopentane
Dr. Wolf's CHM 201 202
16-5
6
Functional Class IUPAC Names of Sulfides
  • analogous to ethers, but replace ether as
    lastword in the name by sulfide.

cyclopentyl methyl sulfide
Dr. Wolf's CHM 201 202
16-6
7
Names of Cyclic Ethers
O
O
O
Oxirane(Ethylene oxide)
Oxolane(tetrahydrofuran)
Oxetane
O
O
O
Oxane(tetrahydropyran)
1,4-Dioxane
Dr. Wolf's CHM 201 202
16-7
8
Names of Cyclic Sulfides
S
S
S
Thiirane
Thiolane
Thietane
S
Thiane
Dr. Wolf's CHM 201 202
16-8
9
Structure and BondinginEthers and Epoxides
  • bent geometry at oxygen analogousto water and
    alcohols, i.e. sp3 hybidization

Dr. Wolf's CHM 201 202
16-9
10
Bond angles at oxygen are sensitiveto steric
effects
O
O
H
H
CH3
H
105
108.5
O
CH3
CH3
112
132
Dr. Wolf's CHM 201 202
16-10
11
An oxygen atom affects geometry in much thesame
way as a CH2 group
most stable conformation of diethyl
etherresembles pentane
Dr. Wolf's CHM 201 202
16-11
12
An oxygen atom affects geometry in much thesame
way as a CH2 group
most stable conformation of tetrahydropyranresemb
les cyclohexane
Dr. Wolf's CHM 201 202
16-12
13
Physical Properties of Ethers
Dr. Wolf's CHM 201 202
16-13
14
Ethers resemble alkanes more than alcoholswith
respect to boiling point
boiling point
  • Intermolecular hydrogenbonding possible in
    alcohols not possible in alkanes or ethers.

36C
35C
O
117C
OH
Dr. Wolf's CHM 201 202
16-14
15
Ethers resemble alcohols more than alkaneswith
respect to solubility in water
solubility in water (g/100 mL)
very small
7.5
  • Hydrogen bonding towater possible for
    ethersand alcohols not possible for alkanes.

O
9
OH
Dr. Wolf's CHM 201 202
16-15
16
Crown Ethers
Dr. Wolf's CHM 201 202
16-16
17
Crown Ethers
  • structure cyclic polyethers derived from
    repeating OCH2CH2 units
  • properties form stable complexes with metal ions
  • applications synthetic reactions involving
    anions

Dr. Wolf's CHM 201 202
16-17
18
18-Crown-6
  • negative charge concentrated in cavity inside
    the molecule

Dr. Wolf's CHM 201 202
16-18
19
18-Crown-6
  • negative charge concentrated in cavity inside
    the molecule

Dr. Wolf's CHM 201 202
16-19
20
18-Crown-6
K
  • forms stable Lewis acid/Lewis base complex with
    K

Dr. Wolf's CHM 201 202
16-20
21
18-Crown-6
K
  • forms stable Lewis acid/Lewis base complex with
    K

Dr. Wolf's CHM 201 202
16-21
22
Ion-Complexing and Solubility
KF
not soluble in benzene
Dr. Wolf's CHM 201 202
16-22
23
Ion-Complexing and Solubility
KF
benzene
add 18-crown-6
Dr. Wolf's CHM 201 202
16-23
24
Ion-Complexing and Solubility
F
K
benzene
18-crown-6 complex of K dissolves in benzene
Dr. Wolf's CHM 201 202
16-24
25
Ion-Complexing and Solubility
K
benzene
F carried into benzene to preserve
electroneutrality
Dr. Wolf's CHM 201 202
16-25
26
Application to organic synthesis
  • Complexaton of K by 18-crown-6 "solubilizes"
    salt in benzene
  • Anion of salt is in a relatively unsolvated
    state in benzene (sometimes referred to as a
    "naked anion")
  • Unsolvated anion is very reactive
  • Only catalytic quantities of 18-crown-6 are
    needed

Dr. Wolf's CHM 201 202
16-26
27
Example
KF
CH3(CH2)6CH2Br
CH3(CH2)6CH2F
18-crown-6
(92)
benzene
Dr. Wolf's CHM 201 202
16-27
28
Preparation of Ethers
Dr. Wolf's CHM 201 202
16-28
29
Acid-Catalyzed Condensation of Alcohols
2CH3CH2CH2CH2OH
CH3CH2CH2CH2OCH2CH2CH2CH3
(60)
Discussed earlier in Section 15.7
Dr. Wolf's CHM 201 202
16-29
30
Addition of Alcohols to Alkenes
H
(CH3)2CCH2 CH3OH
(CH3)3COCH3
tert-Butyl methyl ether
Dr. Wolf's CHM 201 202
16-30
31
The Williamson Ether Synthesis
  • Think SN2!
  • primary alkyl halide alkoxide nucleophile

Dr. Wolf's CHM 201 202
16-31
32
Example
CH3CH2CH2CH2ONa CH3CH2I
CH3CH2CH2CH2OCH2CH3 NaI
(71)
Dr. Wolf's CHM 201 202
16-32
33
Another Example
CH3CHCH3

ONa
(84)
Dr. Wolf's CHM 201 202
16-33
34
Another Example
Alkoxide ion can be derived from primary,
secondary, or tertiary alcohol
Alkyl halide must be primary
CH3CHCH3

ONa
(84)
Dr. Wolf's CHM 201 202
16-34
35
Origin of Reactants
CH3CHCH3
CH2OH
OH
HCl
Na
CH3CHCH3
CH2Cl

ONa
CH2OCHCH3
(84)
CH3
Dr. Wolf's CHM 201 202
16-35
36
What happens if the alkyl halide is not primary?

CH3CHCH3
CH2ONa
Br
Dr. Wolf's CHM 201 202
16-36
37
What happens if the alkyl halide is not primary?

CH3CHCH3
CH2ONa
Br
CHCH3
H2C

CH2OH
Elimination by the E2 mechanism becomesthe major
reaction pathway.
Dr. Wolf's CHM 201 202
16-37
38
Reactions of EthersA Review and a Preview
Dr. Wolf's CHM 201 202
16-38
39
Summary of reactions of ethers
  • No reactions of ethers encountered to this
    point.
  • Ethers are relatively unreactive.
  • Their low level of reactivity is one reason why
    ethers are often used as solvents in chemical
    reactions.
  • Ethers oxidize in air to form explosive
    hydroperoxides and peroxides.

Dr. Wolf's CHM 201 202
16-39
40
Acid-Catalyzed Cleavage of Ethers
Dr. Wolf's CHM 201 202
16-40
41
Example
HBr
CH3CHCH2CH3
CH3CHCH2CH3

CH3Br
heat
OCH3
Br
(81)
Dr. Wolf's CHM 201 202
16-41
42
Mechanism
CH3
Dr. Wolf's CHM 201 202
16-42
43
Mechanism
CH3

Dr. Wolf's CHM 201 202
16-43
44
Mechanism
CH3CHCH2CH3
Br
CH3
HBr

Dr. Wolf's CHM 201 202
16-44
45
Cleavage of Cyclic Ethers
HI
ICH2CH2CH2CH2I
150C
(65)
Dr. Wolf's CHM 201 202
16-45
46
Mechanism
ICH2CH2CH2CH2I


HI
Dr. Wolf's CHM 201 202
16-46
47
Mechanism
ICH2CH2CH2CH2I


HI

O

H
Dr. Wolf's CHM 201 202
16-47
48
Mechanism
ICH2CH2CH2CH2I


HI
HI

O

H
Dr. Wolf's CHM 201 202
16-48
49
Preparation of EpoxidesA Review and a Preview
Dr. Wolf's CHM 201 202
16-49
50
Preparation of Epoxides
Epoxides are prepared by two major methods.Both
begin with alkenes.
  • reaction of alkenes with peroxy acids(Section
    6.19)
  • conversion of alkenes to vicinalhalohydrins,
    followed by treatmentwith base (Section 16.10)

Dr. Wolf's CHM 201 202
16-50
51
Conversion of Vicinal Halohydrinsto Epoxides
Dr. Wolf's CHM 201 202
16-51
52
Example
H
NaOH
O
H2O
H
(81)
Dr. Wolf's CHM 201 202
16-52
53
Example
H
NaOH
O
H2O
H
(81)


O
via


H
H
Br



Dr. Wolf's CHM 201 202
16-53
54
Epoxidation via Vicinal Halohydrins
Br
Br2
H2O
OH
antiaddition
Dr. Wolf's CHM 201 202
16-54
55
Epoxidation via Vicinal Halohydrins
Br
Br2
NaOH
H2O
O
OH
antiaddition
inversion
  • corresponds to overall syn addition ofoxygen to
    the double bond

Dr. Wolf's CHM 201 202
16-55
56
Epoxidation via Vicinal Halohydrins
Br
H3C
Br2
H
NaOH
H3C
H
CH3
H
H2O
H
O
CH3
OH
antiaddition
inversion
  • corresponds to overall syn addition ofoxygen to
    the double bond

Dr. Wolf's CHM 201 202
16-56
57
Epoxidation via Vicinal Halohydrins
Br
H3C
Br2
H3C
H
H
NaOH
H3C
H
H
CH3
CH3
H
H2O
H
O
CH3
OH
antiaddition
inversion
  • corresponds to overall syn addition ofoxygen to
    the double bond

Dr. Wolf's CHM 201 202
16-57
58
Reactions of EpoxidesA Review and a Preview
Dr. Wolf's CHM 201 202
16-58
59
Reactions of Epoxides
  • All reactions involve nucleophilic attack at
    carbon and lead to opening of the ring.
  • An example is the reaction of ethylene oxide
    with a Grignard reagent (discussed in Section
    15.4 as a method for the synthesis of alcohols).

Dr. Wolf's CHM 201 202
16-59
60
Reaction of Grignard Reagentswith Epoxides
R
CH2
CH2
OMgX

H3O
RCH2CH2OH
Dr. Wolf's CHM 201 202
16-60
61
Example
CH2
H2C


O
1. diethyl ether 2. H3O
(71)
Dr. Wolf's CHM 201 202
16-61
62
In general...
Reactions of epoxides involve attack by
anucleophile and proceed with ring-opening.For
ethylene oxide

NuH
NuCH2CH2OH
Dr. Wolf's CHM 201 202
16-62
63
In general...
For epoxides where the two carbons of thering
are differently substituted
Nucleophiles attack herewhen the reaction
iscatalyzed by acids
Anionic nucleophilesattack here
Dr. Wolf's CHM 201 202
16-63
64
Nucleophilic Ring-OpeningReactions of Epoxides
Dr. Wolf's CHM 201 202
16-64
65
Example
NaOCH2CH3
CH3CH2OH
(50)
Dr. Wolf's CHM 201 202
16-65
66
Mechanism


Dr. Wolf's CHM 201 202
16-66
67
Mechanism




Dr. Wolf's CHM 201 202
16-67
68
Mechanism






Dr. Wolf's CHM 201 202
16-68
69
Mechanism










CH3CH2
O
O
CH2CH2
H



Dr. Wolf's CHM 201 202
16-69
70
Example
KSCH2CH2CH2CH3
ethanol-water, 0C
(99)
Dr. Wolf's CHM 201 202
16-70
71
Stereochemistry
OCH2CH3
H
H
OH
(67)
  • Inversion of configuration at carbon being
    attacked by nucleophile
  • Suggests SN2-like transition state

Dr. Wolf's CHM 201 202
16-71
72
Stereochemistry
CH3
H3C
R
R
H
NH3
H
OH
O
H2N
H
R
H2O
S
H
H3C
CH3
(70)
  • Inversion of configuration at carbon being
    attacked by nucleophile
  • Suggests SN2-like transition state

Dr. Wolf's CHM 201 202
16-72
73
Stereochemistry
CH3
H3C
R
R
H
NH3
H
OH
O
H2N
H
R
H2O
S
H
H3C
CH3
(70)
H3C
H
d
d-
O
H3N
H
H3C
Dr. Wolf's CHM 201 202
16-73
74
Anionic nucleophile attacks less-crowded carbon
NaOCH3
CH3OH
(53)
  • consistent with SN2-like transition state

Dr. Wolf's CHM 201 202
16-74
75
Anionic nucleophile attacks less-crowded carbon

1. diethyl ether 2. H3O
(60)
Dr. Wolf's CHM 201 202
16-75
76
Lithium aluminum hydride reduces epoxides
Hydride attacksless-crowdedcarbon
1. LiAlH4, diethyl ether 2. H2O
(90)
Dr. Wolf's CHM 201 202
16-76
77
Acid-Catalyzed Ring-OpeningReactions of Epoxides
Dr. Wolf's CHM 201 202
16-77
78
Example
CH3CH2OH
CH3CH2OCH2CH2OH
H2SO4, 25C
(87-92)
  • CH3CH2OCH2CH2OCH2CH3 formed only on heating
    and/or longer reaction times

Dr. Wolf's CHM 201 202
16-78
79
Example
HBr
BrCH2CH2OH
10C
(87-92)
  • BrCH2CH2Br formed only on heating and/or longer
    reaction times

Dr. Wolf's CHM 201 202
16-79
80
Mechanism

Dr. Wolf's CHM 201 202
16-80
81
Mechanism



Dr. Wolf's CHM 201 202
16-81
82
Figure 16.6 Acid-Catalyzed Hydrolysis of
Ethylene Oxide
Step 1
H2C
CH2
H2C
CH2

O
O


H

H
O


H
Dr. Wolf's CHM 201 202
16-82
83
Figure 16.6 Acid-Catalyzed Hydrolysis of
Ethylene Oxide
Step 2


Dr. Wolf's CHM 201 202
16-83
84
Figure 16.6 Acid-Catalyzed Hydrolysis of
Ethylene Oxide
Step 3




Dr. Wolf's CHM 201 202
16-84
85
Acid-Catalyzed Ring Opening of Epoxides
Characteristics
  • nucleophile attacks more substituted carbon of
    protonated epoxide
  • inversion of configuration at site of
    nucleophilic attack

Dr. Wolf's CHM 201 202
16-85
86
Nucleophile attacks more-substituted carbon
OCH3
CH3OH
CH3CH
CCH3
C
H2SO4
CH3
OH
(76)
  • consistent with carbocation character at
    transition state

Dr. Wolf's CHM 201 202
16-86
87
Nucleophile attacks more-substituted carbon
OCH3
CH3OH
d
d
CH3CH
CCH3
C
H2SO4
CH3
OH
(76)
d
  • consistent with carbocation character at
    transition state

Dr. Wolf's CHM 201 202
16-86b
88
Stereochemistry
H
OH
HBr
H
Br
(73)
  • Inversion of configuration at carbon being
    attacked by nucleophile

Dr. Wolf's CHM 201 202
16-87
89
Stereochemistry
CH3
H3C
R
R
H
H
OH
O
CH3O
H
R
S
H
H3C
CH3
(57)
  • Inversion of configuration at carbon being
    attacked by nucleophile

Dr. Wolf's CHM 201 202
16-88
90
Stereochemistry
CH3
H3C
R
R
H
H
OH
O
CH3O
H
R
S
H
H3C
CH3
H3C
H
d
d
d
H
O
CH3O
H
H
H3C
Dr. Wolf's CHM 201 202
16-89
91
anti-Hydroxylation of Alkenes
H2O
HClO4
H
OH
H
OH
(80)
Dr. Wolf's CHM 201 202
16-90
92
Epoxides in Biological Processes
Dr. Wolf's CHM 201 202
16-91
93
Naturally Occurring Epoxides
  • are common
  • are involved in numerous biological processes

Dr. Wolf's CHM 201 202
16-92
94
Biosynthesis of Epoxides

NADH
enzyme


NAD
C
C
H2O
O
  • enzyme-catalyzed oxygen transfer from O2 to
    alkene
  • enzymes are referred to as monooxygenases

Dr. Wolf's CHM 201 202
16-93
95
Example biological epoxidation of squalene
O2, NADHmonoxygenase
  • this reaction is an important step in the
    biosynthesisof cholesterol

Dr. Wolf's CHM 201 202
16-94
96
Preparation of Sulfides
Dr. Wolf's CHM 201 202
16-95
97
Preparation of RSR'
  • prepared by nucleophilic substitution (SN2)



S
R
NaSCH3
methanol
Dr. Wolf's CHM 201 202
16-96
98
Oxidation of SulfidesSulfoxides and Sulfones
Dr. Wolf's CHM 201 202
16-97
99
Oxidation of RSR'


R
R'
S


sulfide
sulfoxide
sulfone
  • either the sulfoxide or the sulfone can be
    isolated depending on the oxidizing agent and
    reactionconditions

Dr. Wolf's CHM 201 202
16-98
100
Example
water
(91)
  • Sodium metaperiodate oxidizes sulfides to
    sulfoxides and no further.

Dr. Wolf's CHM 201 202
16-99
101
Example
  • 1 equiv of H2O2 or a peroxy acid gives a
    sulfoxide, 2 equiv give a sulfone

H2O2
(2 equiv)
(74-78)
Dr. Wolf's CHM 201 202
16-100
102
Alkylation of SulfidesSulfonium Salts
Dr. Wolf's CHM 201 202
16-101
103
Sulfides can act as nucleophiles




R"
R
X
R"
S
R
S
X

R'
R'
  • product is a sulfonium salt

Dr. Wolf's CHM 201 202
16-102
104
Example

CH3I
CH3(CH2)10CH2SCH3
CH3(CH2)10CH2SCH3
I
CH3
Dr. Wolf's CHM 201 202
16-103
105
Spectroscopic Analysis of Ethers
Dr. Wolf's CHM 201 202
16-104
106
Infrared Spectroscopy
  • CO stretching 1070 and 1150 cm-1 (strong)

Dr. Wolf's CHM 201 202
16-105
107
Figure 16.8 Infrared Spectrum of Dipropyl Ether
CH3CH2CH2OCH2CH2CH3
COC
Wave number, cm-1
Dr. Wolf's CHM 201 202
16-106
108
1H NMR
  • HCO proton is deshielded by O range isca. d
    3.3-4.0 ppm.

d 1.4 ppm
d 0.8 ppm
d 0.8 ppm
CH3 CH2 CH2 OCH2 CH2 CH3
d 3.2 ppm
Dr. Wolf's CHM 201 202
16-107
109
CH3 CH2 CH2 OCH2 CH2 CH3
Chemical shift (d, ppm)
Dr. Wolf's CHM 201 202
16-108
110
13C NMR
Carbons of COC appearin the range d 57-87 ppm.
26.0 ppm
68.0 ppm
Dr. Wolf's CHM 201 202
16-109
111
UV-VIS
Simple ethers have their absorption maximum at
about 185 nm and are transparent to ultraviolet
radiation above about 220 nm.
Dr. Wolf's CHM 201 202
16-110
112
Mass Spectrometry
Molecular ion fragments to give
oxygen-stabilizedcarbocation.

CH3CH2O
CHCH2CH3
m/z 102

CH3


CH3CH2O
CH
CH3CH2O
CHCH2CH3


CH3
m/z 87
m/z 73
Dr. Wolf's CHM 201 202
16-111
113
End of Chapter 16
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