Download OC 2/e Ch 11

11
Organic
Chemistry
William H. Brown &
Christopher S. Foote
11-1
11
Ethers &
Epoxides
Chapter 11
11-2
11 Structure
 The
functional group of an ether is an oxygen
atom bonded to two carbon atoms
 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
11-3
11 Nomenclature: ethers
 IUPAC: the longest carbon chain is the parent.
• name the OR group as an alkoxy substituent

Common names: name the groups attached to oxygen
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)
11-4
11 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
3
1O
Ethylene
oxide
3
4
2
1O
4
4
3
5
2
1O
Tetrahydrofuran Tetrahydropyran
(THF)
O
3
5
2
6
1O
1,4-Dioxane
11-5
11 Physical Properties
 Ethers
are polar
molecules
• oxygen bears a partial
negative charge
• each carbon a partial
positive charge
11-6
11 Physical Properties
 Ethers
are polar molecules but, because of
steric hindrance, only weak dipole-dipole
attractive forces exist between their molecules
in the pure liquid state
 Boiling points of ethers are
• lower than alcohols of comparable MW
• close to those of hydrocarbons of comparable MW
 Ethers
hydrogen bond with H2O and are more
soluble in H2O than are hydrocarbons
11-7
11 Preparation of Ethers
 Williamson
ether synthesis: SN2 displacement
of halide, tosylate, or mesylate by alkoxide ion
CH3
-
CH3 CHO N a
Sodium
isopropoxide
+
+
CH3 I
SN 2
Iodomethane
(Methyl iodide)
CH3
CH3 CHOCH3
+
+ -
Na I
2-Methoxypropane
(Isopropyl methyl ether)
11-8
11 Preparation of Ethers
 Williamson
ether synthesis: yields are
• highest with methyl and 1° halides,
• lower with 2° halides (competing -elimination)
• reaction fails with 3° halides (-elimination only)
CH3
CH3 CBr
-
+ CH3 O N a
CH3
2-Bromo-2methylpropane
+
Sodium
methoxide
E2
CH3
+
CH3 C= CH2 + CH3 OH + N a Br
2-Methylpropene
-
11-9
11 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 is converted to a better one
2 CH3 CH2 OH
Ethanol
H2 SO 4
140°C
CH3 CH2 OCH 2 CH3 + H2 O
Diethyl ether
11-10
11 Preparation of Ethers
• Step 1: proton transfer gives an oxonium ion
:
proton
O
transfer
CH3 CH2 -O- H + H- O-S- O-H
O
O
+
CH3 CH2 -O- H + - :O-S- O-H
H
O
An oxonium ion
• Step 2: nucleophilic displacement of H2O by the OH
group of the alcohol gives a new oxonium ion
:
+
CH3 CH2 -O- H + CH3 CH2 -O- H
H
SN 2
+
CH3 CH2 -O- CH2 CH3 + : O-H
H
A new oxonium ion
H
11-11
11 Preparation of Ethers
Step 3: proton transfer to solvent completes the
reaction
proton
+
transfer
:
+
CH3 CH2 -O- CH2 CH3
O-H
H
H
+
:
CH3 CH2 -O- CH2 CH3 + H O-H
H
11-12
11 Preparation of Ethers
 Acid-catalyzed
addition of alcohols to alkenes:
yields are highest using
• an alkene that can form a stable carbocation
• methanol or a 1° alcohol
CH3
CH3 C= CH2 + CH3 OH
acid
catalyst
CH3
CH3 COCH3
CH3
2-Methoxy-2-methyl
propane
11-13
11 Preparation of Ethers
• Step 1: protonation of the alkene gives a
carbocation
CH3
CH3 C= CH2
+
+ H O CH3
H
CH3
CH3 CCH3 + :O CH3
+
H
• Step 2: reaction of the alcohol (a Lewis base) with
the carbocation (a Lewis acid)
CH3
CH3
:
CH3 CCH3 + HOCH3
+
CH3 CCH3
+
O
CH3
H
11-14
11 Preparation of Ethers
Step 3: proton transfer to solvent completes the
reaction
CH3
:
CH3 O H + CH3 CCH3
+
O
CH3
H
CH3
CH3
+
O H + CH3 CCH3
:O
H
CH3
11-15
11 Cleavage of Ethers
 Ethers
are cleaved by HX to an alcohol and an
alkyl halide
R-O-R + H-X
R-O-H + R-X
• cleavage requires both a strong acid and a good
nucleophile; therefore, the use of concentrated HI
(57%) and HBr (48%)
• cleavage by concentrated HCl (38%) is less
effective, primarily because Cl- is a weaker
nucleophile in water than either I- or Br-
11-16
11 Cleavage of Ethers
A
dialkyl ether is cleaved to two moles of alkyl
halide
( CH3 CH2 CH 2 CH 2 ) 2 O + 2 HBr
Dibutyl ether
heat
2 CH3 CH2 CH2 CH2 Br + H2 O
1-Bromobutane
11-17
11 Cleavage of Ethers
• Step 1: proton transfer to the oxygen atom of the
ether gives an oxonium ion
:
CH3 CH2 -O- CH2 CH3 + H
+
O H
proton
transfer
H
+
CH3 CH2 -O- CH2 CH3 + : O H
H
H
An oxonium ion
• Step 2: nucleophilic displacement on the 1° carbon
Br:
-
+
+ CH3 CH2 -O- CH2 CH3
H
SN 2
CH3 CH2 -Br + : O-CH2 CH3
H
• the alcohol is then converted to the alkyl bromide
or iodide by another SN2 reaction
11-18
11 Cleavage of Ethers
 3°
and benzylic ethers are particularly
sensitive to cleavage by HX
• tert-butyl ethers are cleaved by HCl at room temp
CH3
O-CCH3 + HCl
CH3
SN 1
CH3
OH + Cl-C- CH 3
CH3
• in this case, protonation of the ether oxygen is
followed by C-O cleavage to give the tert-butyl
cation
11-19
11 Oxidation of Ethers
 Ethers
react with O2 at a C-H bond adjacent to
the ether oxygen to give hydroperoxides
• reaction is by a radical chain mechanism
OOH
CH3 CH2 OCH 2 CH3
Diethyl ether
 Hydroperoxide:
+ O2
CH3 CH2 OCH CH 3
A hydroperoxide
a compound containing the
OOH group
11-20
11 Ethers - Protecting Grps
 When
dealing with compounds containing two
or more functional groups, it is often
necessary to protect one of them (to prevent
its reaction) while reacting at the other
 Suppose you wish to carry out this
transformation
HC CCH2 CH2 CH2 OH
4-Pentyn-1-ol
?
CH3 CH2 C CCH2 CH2 CH2 OH
4-Heptyn-1-ol
11-21
11 Ethers - Protecting Grps
• the new C-C bond can be formed by alkylation of
the acetylide anion
• the OH group, however, is more acidic (pKa 16-18)
than the terminal alkyne (pKa 25)
• treating the compound with one mole of NaNH2 will
give the alkoxide anion rather than the acetylide
HC CCH2 CH2 CH 2 OH + N a+ NH 2 4-Pentyn-1-ol
HC CCH2 CH2 CH 2 O- Na + + N H3
11-22
11 Ethers - Protecting Grps
A
protecting group must be
• easily added to the sensitive group
• resistant to reagents used to transform the
unprotected functional group
• easily removed to regenerate the original functional
group
 In
this chapter, we discuss two -OH protecting
groups
• tert-butyl ether group
• trimethylsilyl (TMS) group
11-23
11 Ethers - Protecting Grps
 The
tert-butyl protecting group
• formed by treatment of an alcohol with 2methylpropene in the presence of an acid catalyst
HC CCH2 CH2 CH 2 OH
4-Pentyn-1-ol
1 . CH 2 = C( CH3 ) 2
H2 SO 4
CH3
HC CCH2 CH2 CH 2 OCCH3
CH3
11-24
11 Ethers - Protecting Grps
• the unprotected alkyne is alkylated
CH3
HC CCH2 CH2 CH 2 OCCH3
CH3
2 . Na + NH2 3 . CH 3 CH 2 Br
CH3
CH3 CH2 C CCH2 CH2 CH 2 OCCH3
CH3
11-25
11 Ethers - Protecting Grps
• the tert-butyl protecting group is removed by
treatment with aqueous acid
CH3
CH3 CH2 C CCH2 CH2 CH 2 OCCH3
4 . H3 O + / H2 O
CH3
CH3 CH2 C CCH2 CH2 CH 2 OH + H2 C C( CH3 ) 2
4-Heptyn-1-ol
11-26
11 Ethers - Protecting Grps
 Trimethylsilyl
(TMS) group
• treat the alcohol with chlorotrimethylsilane in the
presence of a 3° amine, such as triethylamine
• the function of the 3° amine is to catalyze the
reaction and to neutralize the HCl
CH3
RCH2 OH
+ Cl-Si- CH3
( CH3 CH2 ) 3 N
CH3
Chlorotrimethylsilane
CH3
RCH2 O- Si-CH3
CH3
A trimethylsilyl
ether
11-27
11 Ethers - Protecting Grps
• the TMS group is removed by treatment with
aqueous acid or with F- in the form of
tetrabutylammonium fluoride
CH3
RCH2 O- Si-CH3 + H2 O
CH3
H
+
CH3
RCH2 OH + HO- Si-CH3
CH3
A trimethylsilyl
ether
11-28
11 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
CH2
1O
Oxirane
(Ethylene oxide)
H3 C
H
H
C
C
CH3
O
cis-2,3-Dimethyloxirane
(cis-2-Butene oxide)
1
H
O
2
H
1,2-Epoxycyclohexane
(Cyclohexene oxide)
11-29
11 Synthesis of Epoxides-1
 Ethylene
oxide, one of the few epoxides
manufactured on an industrial scale, is
prepared by air oxidation of ethylene
2 CH2 = CH2 + O 2
Ag
2 H2 C
CH2
O
Oxirane
(Ethylene oxide)
11-30
11 Synthesis of Epoxides-2
 The
most common laboratory method is
oxidation of an alkene using a
peroxycarboxylic acid (a peracid)
O
COOH
O
COOH
CO
Cl
meta- chloroperoxybenzoic acid
(MCPBA)
O
Mg
2
2+
O
CH3 COOH
Peroxyacetic acid
(Peracetic acid)
Magnesium
monoperoxyphthalate
(MMPP)
11-31
11 Synthesis of Epoxides-2
 Epoxidation
+
Cyclohexene
of cyclohexene
O
RCOOH
CH2 Cl 2
A peroxycarboxylic acid
H
O
H
1,2-Epoxycyclohexane
(Cyclohexene oxide)
+
O
RCOH
A carboxylic
acid
11-32
11 Synthesis of Epoxides-2
 Epoxidation
is stereospecific:
• epoxidation of cis-2-butene gives only cis-2,3dimethyloxirane
• epoxidation of trans-2-butene gives only trans-2,3dimethyloxirane
H3 C
CH3
C
H
C
H
cis-2-Butene
RCO 3 H
H3 C
H
C
C
CH3
H
O
cis-2,3-Dimethyloxirane
11-33
11 Synthesis of Epoxides-2
A
mechanism for alkene epoxidation must
take into account that the reaction
• takes place in nonpolar solvents, which means that
no ions are involved
• is stereospecific with retention of the alkene
configuration, which means that even though the pi
bond is broken, at no time is there free rotation
about the remaining sigma bond
11-34
11 Synthesis of Epoxides-2
A
mechanism for alkene epoxidation
R
O
R
C
O
3
2
H
O
C
H
O
O
4
O
1
C
C
C
C
11-35
11 Synthesis of Epoxides-3
A
second general method involves
1. treatment of an alkene with Cl2 or Br2 in H2O to give
a halohydrin; reaction is stereospecific
2. treatment of the halohydrin with base, causing an
internal SN2
CH 3 CH= CH2
Propene
Cl 2 , H2 O
Cl
CH 3 CH- CH 2
Na OH, H2 O
HO
1-Chloro-2-propanol
(a chlorohydrin)
CH3 CH CH2
O
Methyloxirane
(Propylene oxide)
11-36
11 Synthesis of Epoxides-3
Problem: given the stereospecificity of this scheme,
show that cis-2-butene gives cis-2,3-dimethyloxirane
H
H3 C
H
1 . Cl 2 , H2 O
C C
CH3 2 . Na OH, H2 O
cis-2-Butene
H3 C
H
C
C
H
CH3
O
cis-2,3-Dimethyloxirane
11-37
11 Synthesis of Epoxides-4
 Sharpless
epoxidation
• stereospecific and enantioselective
R2
R1
T i( OiPr) 4
(+)-Diethyl
tartrate
R2
R1
+ t e r t - BuOOH
R3
CH2 OH
O
CH2 OH
A
R3
R2
(-)-Diethyl
tartrate
R1
O
T i( OiPr) 4
R3
CH2 OH
B
11-38
11 Reactions of Epoxides
 Because
of the strain associated with the
three-membered ring, epoxides readily
undergo a variety of ring-opening reactions
Nu
C
C
O
+ HN u :
C
C
HO
11-39
11 Reactions of Epoxides
 Acid-catalyzed
ring opening
• in the presence of an acid catalyst, epoxides are
hydrolyzed to glycols
O + H2 O
Oxirane
(Ethylene oxide)
H+
HO
OH
1,2-Ethanediol
(Ethylene glycol)
11-40
11 Reactions of Epoxides
Step 1: proton transfer to the epoxide gives a bridged
oxonium ion intermediate
H2 C
CH2
:
O
+
+ H O H
H
CH2 + H2 O :
H2 C
O+
H
Step 2: backside attack of H2O on the protonated
epoxide opens the three-membered ring
H
H + H
O
:
O
H
H2 C
CH 2
O+
H
H2 C
CH 2
O:
H
11-41
11 Reactions of Epoxides
Step 3: proton transfer to solvent completes the
hydrolysis
H
:
O
H
H
H
+O
H2 C CH2
H
H2 C
O:
CH2
O
O
H
H
+
+ H O H
H
11-42
11 Reactions of Epoxides
 Attack
of the nucleophile on the protonated
epoxide shows anti stereoselectivity
• hydrolysis of an epoxycycloalkane gives a trans1,2-diol
H
O
OH
+
H
1,2-Epoxycyclopentane
(Cyclopentene oxide)
H2 O
H+
OH
trans -1,2-Cyclopentanediol
11-43
11 Reactions of Epoxides
 Compare
the stereochemistry of the glycols
formed by these two methods
H
OH
+
RCO 3 H
O
H
H2 O
H
OH
trans-1,2-Cyclopentanediol
OH
OsO 4 , t-BuOOH
OH
cis-1,2-Cyclopentanediol
11-44
11 Reactions of Epoxides
 Ethers
are not normally susceptible to attack
by nucleophiles
 Because of the strain associated with the
three-membered epoxide ring, epoxides
undergo nucleophilic ring opening readily
11-45
11 Reactions of Epoxides
 Nucleophilic
ring opening is stereospecific
• attach of the nucleophile is anti to the leaving
group
H
O + CH3 OH
H
Cyclohexene oxide
-
CH3 O N a
+
OH
OCH3
trans-2-Methoxycyclohexanol
11-46
11 Reactions of Epoxides
CH3
CH3
HOCH2 CH OH
A glycol
HSCH 2 CHOH
A-mercaptoalcohol
H2 O/ H3 O +
N a+ SH - / H 2 O
CH3
H2 C
N a+ C N - / H 2 O
CH3
N CCH2 CHOH
A-hydroxynitrile
CH3
CH
O
Methyloxirane
HC CCH2 CHOH
A-alkynylalcohol
+
1 . HC C N a
2 . H2 O
N H3
CH3
H2 N CH 2 CHOH
A-aminoalcohol
11-47
11 Reactions of Epoxides
 Treatment
of an epoxide with lithium
aluminum hydride, LiAlH4, reduces the
epoxide to an alcohol
• the nucleophile attacking the epoxide ring is
hydride ion, H:CH
CH2
O
Phenyloxirane
(Styrene oxide)
1 . LiA lH4
2 . H2 O
CH- CH 3
OH
1-Phenylethanol
11-48
11 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
11-49
11 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+
11-50
11 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: list the groups bonded to sulfur followed
by the word sulfide
CH3
CH3 CH2 SCH2 CH3
CH3 CH2 SCHCH3
Ethylsulfanylethane
(Dimethyl sulfide)
2-Ethylsulfanylpropane
(Ethylisopropyl sjulfide)
11-51
11 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
H3 C
S
CH3
Methyldisulfanylmethane
(Dimethyldisulfide)
11-52
11 Preparation of Sulfides
 Symmetrical
sulfides: treat one mole of Na2S
with two moles of an alkyl halide
RSR + 2 N aX
A sulfide
2 RX + N a2 S
Cl
Cl
+
1,4-Dichlorobutane
Na2 S
SN 2
+
2 Na
+
Cl
-
S
Thiolane
(Tetrahydrothiophene)
11-53
11 Preparation of Sulfides
 Unsymmetrical
sulfides: convert a thiol to its
sodium salt and then treat this salt with an
alkyl halide (a variation on the Williamson
ether synthesis)
+ CH3I
CH3(CH2)8CH2S- Na+
Sodium 1-decanethiolate
SN2
CH3(CH2)8CH2SCH3 + Na+ I1-Methylsulfanyldecane
(Decyl methyl sulfide)
11-54
11 Oxidation Sulfides
 Sulfides
can be oxidized to sulfoxides and
sulfones by the proper choice of experimental
conditions
S- CH3
Methyl phenyl
sulfide
H2 O2
25oC
O
N aIO 4
S- CH3
o
25 C
Methyl phenyl
sulfoxide
O
S- CH3
O
Methyl phenyl
sulfone
11-55
11 Prob 11.13
Account for the fact that tetrahydrofuran is
considerably more soluble in water than diethyl ether.
O
Diethyl ether
8 g/100 mL water
O
Tetrahydrofuran
very soluble in water
11-56
11 Prob 11.15
Which ethers can be prepared by a Williamson
synthesis? For those can can’t, explain why not.
CH3
(a) CH3 CH2 OCH CH 3
CH3
(b) CH3 COCH2 CH2 CH3
CH3
OCH3
(c)
(e)
CHCH3
OCH2 CH3
(d)
(f)
CH3
O CH2
OC( CH3 ) 3
11-57
11 Prob 11.16
Propose a mechanism for this reaction.
CH= CH2 + CH3 OH
H2 SO 4
OCH3
CHCH3
11-58
11 Prob 11.17
Draw structural formulas for the products when each
compound is refluxed with concentrated HI.
(a)
O
(b)
O
O
(c)
O
(d)
O
11-59
11 Prob 11.18
Write a pair of chain propagation steps for this radical
chain reaction. Assume initiation is by a radical R•.
Account for the regioselectivity of the
hydroperoxidation.
O
+ O2
Diisopropyl ether
O
O
OH
A hydroperoxide
11-60
11 Prob 11.20
Propose a mechanism for each reaction.
H2 C
CH2 + CH3 OH
H2 SO 4
O
Oxirane
(Ethylene oxide)
H2 C
CH2 + CH3 CH2 OH
O
Oxirane
(Ethylene oxide)
CH3 OCH2 CH 2 OH
2-Methoxyethanol
(Methyl Cellosolve)
H2 SO 4
CH3 CH2 OCH 2 CH2 OH
2-Ethoxyethanol
(Cellosolve)
11-61
11 Prob 11.21
Propose a mechanism for each step in this synthesis.
O
OH
+ HO
HO
H
O
+
OH
H
+
O
O
1,4-Dioxane
11-62
11 Prob 11.22
Propose a synthesis of each compound from ethylene
oxide and any readily available alcohols.
(a)
O
O
(b)
O
O
O
11-63
11 Prob 11.25
How many stereoisomers are possible for 2-chloro1,2-diphenylethanol? Which of the possible
stereoisomers are formed in this reaction?
C6 H 5
C6 H5
H
+ HCl
C
H
C
O
trans-2,3-Diphenyloxirane
C6 H5 CH-CHC6 H 5
HO
Cl
2-Chloro-1,2-diphenylethanol
11-64
11 Prob 11.26
Propose a mechanism for this rearrangement.
O
BF3
O
Tetramethyloxirane
3,3-Dimethyl-2-butanone
11-65
11 Prob 11.27
Account for the stereospecificity of this epoxide ring
opening reaction.
CH3
+ H2 O
O
H
HO
H2 SO 4
CH3
HO
CH3
+
HO
H
Only this glycol
is formed
HO
H
This glycol is
not formed
11-66
11 Prob 11.28
If the starting alkene is trans, what is the configuration
of the epoxide formed in each sequence?
PhCH= CHPh
1,2-Diphenylethylene
RCO 3 H
O
PhCH CHPh
2,3-Diphenyloxirane
O
1 . Cl 2 , H2 O
PhCH CHPh
+
2 . CH 3 O N a
1,2-Diphenylethylene
2,3-Diphenyloxirane
PhCH= CHPh
11-67
11 Prob 11.29
Show how this chiral epoxide can be prepared from an
allylic alcohol precursor using the Sharpless
epoxidation.
O
HO
O
O
11-68
11 Prob 11.30
Assume reaction here is by HOCl, which behaves as if
it were Cl+OH-. Account for the observed
regiochemistry and stereochemistry.
CH3
CH3
R
white blood
cells
HO
Cholesterol
CH3
CH3
OH
R
HO
Cl
11-69
11 Prob 11.31
Propose a mechanism for this rearrangement.
O
O
H2 SO 4 , TH F
11-70
11 Prob 11.34
Show how to convert cyclohexene to these
compounds.
(a)
OH
OH
O
(c)
(b)
OH
(d)
OH
OH
O
N H2
(f)
(e)
OCH3
OH
OCH3
Br
(g)
SCH2 CH 3
(h)
(i)
OH
11-71
11 Prob 11.34 (cont’d)
Show how to convert cyclohexene to these
compounds.
(j)
OH
SH
(k)
(m)
(l)
CN
Cl
OH
OH
O
O
(n) HC(CH2 ) 5 CH
C CCH3
11-72
11 Prob 11.35
Show reagents for each reaction.
Br
(c)
(e)
(b)
Br
(d)
(a)
O
OH
OH
OH
C CH
(f)
OH
(g)
OCH3
(i)
(j)
OH
OH
OH
N
(k)
O
H
O
H
(h)
O
OCH3
11-73
11 Prob 11.36
Given this retrosynthetic analysis, propose a
synthesis for the target molecule.
OH
O
O
+
HO
Cl
Styrene
1-chloro-3-methyl2-butene
11-74
11 Prob 11.38
Propose structural formulas for A, B, C, and D, and the
type of mechanism by which each is formed.
CH 2 = CHCH 3
Propene
Cl 2
heat
Cl 2 , H2 O
A ( C3 H5 Cl)
C ( C3 H 7 ClO2 )
N aOH, H 2 O
Ca( OH) 2
heat
H2 O, HCl
B ( C3 H6 O)
D ( C3 H 6 O2 )
OH
HOCH2 CHCH2 OH
1,2,3-Propanetriol
(glycerol, glycerin)
11-75
11 Prob 11.39
Following are steps in the synthesis of gossyplure.
OH
7
OH
8
+
O
9
Br
+ HC CH
11-76
11 Prob 11.39 (cont’d)
continuing from step 7 of the previous screen
O
C CH + Br
5
4
Br + HC CH
Br
OH
6-Bromo-1-hexanol
6
OH
7
11-77
11 Prob 11.39 (cont’d)
continuing from step 4 of the previous screen
OH
1
O
2
O
3
C CH + Br
O
11-78
11 Prob 11.40
Propose a mechanism for each step and account for
the regiospecificity of Steps 1 and 2.
+ Cl 2 500°C
Step 1:
Propene
+
Cl
HCl
3-Chloropropene
(Allyl chloride)
OH
Step 2:Cl
+ Cl 2 / H2 O
Cl
Cl + HCl
OH
Step 3: Cl
Cl + Ca( OH) 2
O
+ CaCl 2
3-Chloro-1,2-epoxypropane
(Epichlorohydrin)
Cl
11-79
11
Ethers
&
Epoxides
K+
End of Chapter 11
11-80