Transcript Chapter 7 Alkene Synthesis & Reactions 5/24/2016

Chapter 7
Alkene
Synthesis & Reactions
5/24/2016
Chapter 7
1
sp2  sp3
p 172, Table 5.3
Diss. energy of double bond (H2C=CH2):
611 kJ/mol
Diss. energy of sigma bond (CH3 — CH3): 376 kJ/mol
Dissociation energy of pi bond:
235 kJ/mol
Therefore, pi bond is more reactive than sigma bond.
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Chapter 7
2
General Properties
No rotation about the pi bond.
Relatively nonpolar. Not soluble in water, but soluble in hexane,
ether, etc.
H
alkyl
401 kJ/mol
H
H H
allylic
361 kJ/mol
H
p 172, Table 5.3
Vinylic C—H
444 kJ/mol
1. Radical reactions take place at the allylic position.
2. Allylic hydrogen is more acidic than alkyl and vinylic hydrogen.
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Chapter 7
3
Alkene Synthesis
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Chapter 7
4
Synthesis
From halides - dehydrohalogenation (minus HX):
Br
H
KOH
CH3CH2OH
Elimination
From alcohol - dehydration (minus H2O):
H3C
OH
H
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CH3
H2SO4, H2O
THF
Chapter 7
5
Elimination Reaction
Br
KOH
CH3CH2C(CH3)2
CH3CH2OH
OH
CH3CH2CCH2CH2CH3
H2SO4, H2O
THF
CH3
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Chapter 7
6
Br
CH3
KOH
CH3CH2C(CH3)2
CH3CH2OH
C(CH3)2
CH3CH
2-Methyl-2-butene
+
CH3CH2C
CH2
2-Methyl-1-butene
OH
CH3CH2CCH2CH2CH3
H2SO4, H2O
CCH2CH2CH3
CH3CH
3-Methyl-2-hexene (E and Z)
THF
CH3
CH3
CH3CH2CCH2CH2CH3
2-Ethyl-1-pentene
CH2
CH3CH2 C
CHCH2CH3
3-Methyl-3-hexene (E and Z)
CH3
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Chapter 7
7
Alkene Reactions
5/24/2016
Chapter 7
8
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
5/24/2016
syn
syn
hydroxylation
Chapter 7
9
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
5/24/2016
syn
syn
hydroxylation
Chapter 7
10
Alkene + HX
X: Cl, Br, or I.
Carbocation intermediate -
is planar, incoming
group can attack from above or below the plane.
Markovnikov rule - regiochemistry.
Review Chapter 6.
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Chapter 7
11
Alkene + HX
Electrophilic Addition.
CH2
CH
HBr
HBr
CHCH3
CH3CH
HCl
?
2-Chloro-3-methylheptane
et her
CH3
+
HBr
+
HCl
ether
CH3
CH3
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ether
Chapter 7
12
CH2
CH
CH3CH
HBr
CHCH3
CHBrCH3
HBr
CH3CHBrCH2CH3
CH3
CH3
CH2
CHCHCH2CH2CH2CH3
+
HCl
ether
CH3CHClCHCH2CH2CH2CH3
CH3
CH3
+
HBr
+
ether
Br
CH3
CH3
+
Br
Br
E&Z
E&Z
CH3
+
CH3
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HCl
ether
Chapter 7
CH3
CH3
Cl
CH3
CH3
Cl
13
Alkene + HX - suppliment
CH
CH
CH2
CH2
HBr
CHBrCH3
HBr
CH2CH2Br
Secondary halide - carbocation.
Primary halide - free radical.
ROOR
RO
2 RO
OR
RO
+
CH
+
ROH
HBr
Br

CH2
CHCH2Br
+
Br

CHCH2Br
CH2CH2Br
+
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H
Br
Chapter 7
14
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
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syn
syn
hydroxylation
Chapter 7
15
Alkene + X2
X: Cl or Br. F is too reactive, I does not react.
Chloronium or bromonium ion intermediate.
Anti stereochemistry.
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Chapter 7
16
Alkene + X2
CH3
+
Cl2
CH3
CH2 Cl2
Br2
CH3CH
CH2
CH3
CH3
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Br2
Chapter 7
17
Cl
CH3
+
Cl2
CH3
CH2Cl2
CH3
CH3
Cl
trans-1,2,Dichloro-1,2-dimethylcyclohexane
Br2
CH3CH
CH3CHBrCH2Br
CH2
1,2,Dibromopropane
CH3
CH3
CH3
Br2
CH3
Br
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Chapter 7
Br
18
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
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syn
syn
hydroxylation
Chapter 7
19
Halohydrin
Alkene  halohydrin.
O
CH3SCH3
O
N Br
DMSO - solvent, NBS - source of Br2.
O
Form bromonium ion intermediate. Then attack
by nucleophile.
Aromatic ring is inert.
Anti stereochemistry.
Markovnikov rule applies.
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Chapter 7
20
Halohydrin
Br2
CH3CH
CH2
H2O
NBS
CH3CH
CH2
H2O/DMSO
Br 2
H2O
CH3
Cl2
H2O
CH3
Br2
Satd.NaCla q
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Chapter 7
21
Br2
CH2
CH3CH
CH3CHOHCH2Br
1-bromo-2-propanol
H2O
NBS
CH3CHOHCH2Br
CH2
CH3CH
H2O/DMSO
Br
Br2
H2O
trans-2-bromocyclopentanol or
cyclopentene bromohydrin
OH
CH3
CH3
OH
Cl2
(E)-2-Chloro-1-methly-1-cyclopentanol
H2O
Cl
CH3
Br2
CH3
OH
Satd.NaClaq
+
Br
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CH3
Cl
Br
Chapter 7
22
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
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syn
syn
hydroxylation
Chapter 7
23
Oxymercuration
Alkene  alcohol.
Intermediate is mercurinium ion (similar to
bromonium ion).
Anti stereochemistry.
Markovnikov rule applies.
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Chapter 7
24
Oxymercuration
HgAc2, H2O/THF
CH3CH2CH2CH
CH3CH2CH
CH2
NaBH4
C(CH3)2
HgAc2 , H2 O/THF
NaBH4
OH
HgAc2, H2O/THF
?
NaBH4
(CH3)2CCH2CH2CH2CH3
OH
?
?
CH3
HgAc2 , H2 O/THF
NaBH4
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Chapter 7
25
HgAc2, H2O/THF
CH3CH2CH2CH
C(CH3)2
CH3CH2CH
CH2
CH2
NaBH4
HgAc2, H2O/THF
CH3CH2CH2COH(CH3)2
NaBH4
C(CH3)CH2CH2CH2CH3
or
(CH3)2C
CH3CH2CH2CHOHCH3
OH
HgAc2, H2O/THF
CHCH2CH2CH3
NaBH4
(CH3)2CCH2CH2CH2CH3
OH
HgAc2 , H2 O/THF
NaBH4
CH3
HO
HgAc2, H2O/THF
CH3
NaBH4
5/24/2016
Chapter 7
26
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
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syn
syn
hydroxylation
Chapter 7
27
Hydroboration
Alkene  alcohol.
Intermediate is organoborane.
Syn stereochemistry.
Non - Markovnikov rule applies.
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Chapter 7
28
Hydroboration Mechanism
C C
H B
H
H
H
H
H
C C
H B
+
C C
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C
BH3
H2O2
B
C
BH3
OH-
Chapter 7
H
H
OH-
3
H2O2
B
C C
H
H
3 C C
H
B
C
C
H
OH
3
C
C
H
OH
29
Hydroboration
CH3CH2CH2CH
CH3CH2CH
CH2
C(CH3)2
BH3, THF
H2O2, OH-
BH3, THF
H2O2, OHBH3, THF
?
H2O2, OH-
CH2(OH)C(CH3)2CH2CH2CH2CH3
BH3, THF
H2O2, OH-
CH3
CH3
BH3, THF
H2O2, OH-
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OH
Chapter 7
30
CH3CH2CH2CH
CH3CH2CH
CH2
CH2
C(CH3)2
BH3, THF
H2O2,
CH3CH2CH2CH2CH2OH
OH-
BH3, THF
CH3CH2CH(OH)CH(CH3)2
H2O2, OH-
C(CH3)CH2CH2CH2CH3
BH3, THF
BH3, THF
H2O2,
OH-
CH2(OH)C(CH3)2CH2CH2CH2CH3
OH
H2O2, OH-
CH3
BH3, THF
H2O2, OH-
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CH3
OH
Chapter 7
31
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
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syn
syn
hydroxylation
Chapter 7
32
Hydrogenation
•
•
•
•
Reduction - formation of C—H bond.
PtO2 solid catalyst - heterogeneous reaction.
syn chemistry.
“Alkenes are much more reactive than most
other functional groups toward catalytic
hydrogenation.” - p251
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Chapter 7
33
Hydrogenation
(CH3)2C=CHCH2CH3
H3C
+
+
H2
H2
Pd/C
Pd/C
H3C
CH=CH2
+
H2
Pd/C
O
OMe
5/24/2016
+
H2
Chapter 7
Pd/C
34
(CH3)2C=CHCH2CH3
H3C
+
+
H2
H2
(CH3)2CHCH2CH2CH3
Pd/C
Pd/C
H3C
H3C
H3C
CH2CH3
CH=CH2
+
H2
Pd/C
O
O
OMe
5/24/2016
+
H2
OMe
Pd/C
Chapter 7
35
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
5/24/2016
syn
syn
hydroxylation
Chapter 7
36
Hydroxylation
• Forming 1,2-dialcohol or diol (glycol).
• Forming cyclic osmate intermediate
therefore syn stereochemistry.
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Chapter 7
37
Hydroxylation
CH3CH2C=C(CH3)2
OsO4 Py
NaHSO4
OsO4 Py
CH3
NaHSO4
OsO4 Py
NaHSO4
5/24/2016
Chapter 7
38
HO OH
CH3CH2C=C(CH3)2
CH3
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OsO4 Py
NaHSO4
CH3CH2CHCCH3
CH3
OsO4 Py
OH
CH3
NaHSO4
OH
OsO4 Py
OH
NaHSO4
OH
Chapter 7
39
Breaking up 1,2-diol
O
HO OH
CH3CH2C=C(CH3)2
OsO4 Py
CH3
5/24/2016
NaHSO4
CH3CH2CHCCH3
HIO4
H2O, THF
CH3CH2CH
+
(CH3)2C=O
CH3
OsO4 Py
OH
CH3
NaHSO4
OH
Chapter 7
O
H
HIO4
H2O, THF
O
CH3
40
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
5/24/2016
syn
syn
hydroxylation
Chapter 7
41
Alkene + Carbene
H
H
CH3
+
KOH
CHCl3
CH3
CH2CH3
CH2CH3
+
Cl
H
Cl H
CHCl3
KOH
Cl
+
KCl
Cl
5/24/2016
Chapter 7
42
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
5/24/2016
syn
syn
hydroxylation
Chapter 7
43
Simmons-Smith Reaction
+
(CH3)2CHCH2CH=CHCH3
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Zn(Cu)
CH2I2
+
ether
CH2 I2
Zn(Cu)
ether
Chapter 7
(CH3)2CHCH2CH
CHCH3
44
Alkene + Carbene
CH3
(CH3)2CHCH2CH
+
C=C
CH2 I2
(CH3)2CHCH2CH
ether
H
H
H
(CH3)2CHCH2CH
Zn(Cu)
+
C=C
H
Zn(Cu)
CH2 I2
ether
CH3
CH3
H
H
(CH3)2CHCH2CH
H
H
CH3
p 248 “…stereospecific … Starting from a cis alkene … only cis
disubstituted cyclopropane is produced; starting from a trans alkene,
only trans-disubstituted cyclopropane is produced.”
5/24/2016
Chapter 7
45
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
5/24/2016
syn
syn
hydroxylation
Chapter 7
46
Oxidation
• Reducing the length of the carbon skeleton.
• Alkene  aldehyde and/or ketone.
• Oxidizing agents are ozone or potassium
permanganate.
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Chapter 7
47
Alkene + Ozone
(CH3)2CHCH2CH=CHCH3
O3
Zn, H3O+
O3
(CH3)2C=CH2
Zn, H3O+
CH3
CH3
O3
Zn, H3O+
5/24/2016
Chapter 7
48
O
O
(CH3)2CHCH2CH=CHCH3
(CH3)2C=CH2
O3
+
(CH3)2CHCH2CH
CHCH3
Zn, H3O+
O3
Zn, H3O+
(CH3)2C=O
+
O=CH2
CH3
CH3
O3
Zn, H3O+
5/24/2016
Chapter 7
O
+
(CH3)2C=O
49
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
5/24/2016
syn
syn
hydroxylation
Chapter 7
50
Oxidation
Alkene + Ozone
(CH3)2CHCH2CH=CHCH3
Alkene + KMnO4
O3
Zn, H3O+
(CH3)2CHCH2CH=CHCH3
O3
(CH3)2C=CH2
(CH3)2C=CH2
Zn, H3O+
O3
CH3
KMnO4
H3O+
KMnO4
H3O+
Zn, H3O+
5/24/2016
H3O+
CH3
CH3
CH3
KMnO4
Chapter 7
51
Alkene + KMnO4
(CH3)2CHCH2CH=CHCH3
(CH3)2C=CH2
KMnO4
H3O+
KMnO4
H3O+
CH3
CH3
KMnO4
H3O+
5/24/2016
Chapter 7
52
O
O
(CH3)2CHCH2CH=CHCH3
KMnO4
H3O+
(CH3)2CHCH2COH
+
CH3COH
O
(CH3)2C=CH2
KMnO4
(CH3)2COH
H3O+
+
CO2
CH3
CH3
KMnO4
H3O+
5/24/2016
O
+
H3C
C
O
H3C
Chapter 7
53
Additional KMnO4 Reaction
KMnO4
H3O+, cold
KMnO4
H3O+, hot
5/24/2016
Chapter 7
OH
OH
O
C OH
C O
OH
54
M
halogenation
anti
X
X
X
O
halohydrination
oxidation
HO
M
anti
X
HO
O
oxymercuration
O
HgAc2, H2O/THF
oxidation
Alkene
M
HO
NaBH4
hydroboration
syn Simmons-Smith
HO
non-M
syn
hydrogenation
Cl
syn
Cl
carbenation
HO
HO
5/24/2016
syn
syn
hydroxylation
Chapter 7
55
Polymerization
• Monomer  Polymer
• Process - initiation, propagation, and
termination.
• Monomer unit = repeating unit.
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Chapter 7
56
Polymerization
monomer
polymer
H2C=CH2
---CH2CH2CH2CH2CH2CH2---
Monomer unit
CH3
H2C=CHCH3
CH3
CH3
CH3
CH3
CH2CHCH2CHCH2CHCH2CHCH2CH
Monomer unit
5/24/2016
Chapter 7
57
Polymerization Mechanism
Initiation
OR
RO
heat
O
2 RO
O
C-O-O-C
Propagation
RO
+
.
CH2=CHCH3
ROCH2CHCH3
5/24/2016
.
ROCH2CHCH3
CH3
+
CH2=CHCH3
.
ROCH2CHCH2CHCH3
Chapter 7
58
Alkene
Sample Problems
5/24/2016
Chapter 7
59
What reagents would you use to synthesize each of the following
compounds starting with …
HO
HO
(a)
(b)
O
OH
Br
(c)
(d)
MeO
OH
(e)
5/24/2016
(f)
Chapter 7
(g)
60
(a) HgAc2, THF/H2O, NaBH4
(b) HBr, ROOR
(c) OsO4, NaHSO3, H2O
(d) KMnO4, H3O+
(e) BH3, THF, H2O2, OH(f) CH2I2, Zn, ether
(g) HgAc2, THF/CH3OH, NaBH4
5/24/2016
Chapter 7
61
Show the structures when
reagents.
react with the following
1) Borane in tetrahydrofuran, followed by basic hydrogen peroxide.
2) Ozone followed by zinc in acid medium.
3) Hot, concentrated potassium permanganate.
4) Hydrogen and platinum catalyst.
5) Hydrogen bromide in methylene chloride.
6) Bromine water.
7) Chlorine gas.
8) Methylene iodide pretreated with the zinc-copper alloy.
9) Mercuric acetate in methanol, followed by sodium borohydride.
5/24/2016
Chapter 7
62
Br
5)
HO
Br
OH
1)
Br
H3C
6)
2)
O
O
O
H
3)
Cl
+
O
O
OH
7)
Cl
Cl
Cl
O
+
CO2
4)
5/24/2016
HO
O
H
Br
OH
8)
9)
Chapter 7
MeO
OMe
63
Page 270, problem 7.44
Compound A has the formula C8H8. It reacts rapidly with
KMnO4 to give CO2 and a carboxylic acid, B (C7H6O2),
but reacts with only 1 molar equivalent of H2 on catalytic
hydrogenation over a palladium catalyst. On hydrogenation
under conditions that reduce aromatic rings, 4 equivalents of
H2 are taken up, and hydrocarbon C (C8H16) is produced.
What are the structures of A, B, and C? Write the reactions.
5/24/2016
Chapter 7
64
O
KMnO4
+
CO2
+
H
H2
Pd/C
H2
5/24/2016
Chapter 7
65
In contact with a platinum catalyst, an unknown alkene
reacts with three moles of hydrogen gas to give 1-isopropyl4-methylcyclohexane. When the unknown alkene is,
ozonized and reduced, the products are the following:
H
O
O
O
C
C
C
H
H
C
H H
5/24/2016
C
CH3
O
Chapter 7
H3C
O
O
C
C
C
H
H H
66
H3C
O
O
C
C
C
O
H
H
C
H
H H
All three steps use
O3 and Zn, H+,
H
O
O
C
C
C
H H
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Chapter 7
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