15.6 Reactions of Alcohols: A Review and a Preview

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15.6Reactions of AlcoholsA Review and a Preview
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Table 15.2 Review of Reactions of Alcohols

• reaction with hydrogen halides
• reaction with thionyl chloride
• reaction with phosphorous tribromide
• acid-catalyzed dehydration
• conversion to p-toluenesulfonate esters

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New Reactions of Alcohols in This Chapter

• conversion to ethers
• esterification
• esters of inorganic acids
• oxidation
• cleavage of vicinal diols

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15.7Conversion of Alcohols to Ethers
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Conversion of Alcohols to Ethers
H

• acid-catalyzed
• referred to as a "condensation"
• equilibrium most favorable for primary alcohols

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Example
2CH3CH2CH2CH2OH
CH3CH2CH2CH2OCH2CH2CH2CH3
(60)
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Figure 15.2 Mechanism of Formation of Diethyl
Ether
Step 1
H
H



OSO2OH
CH3CH2O

H
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Figure 15.2 Mechanism of Formation of Diethyl
Ether
Step 2

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Figure 15.2 Mechanism of Formation of Diethyl
Ether
Step 3

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Intramolecular Analog
HOCH2CH2CH2CH2CH2OH
130
H2SO4

• reaction normally works wellonly for 5- and
  6-memberedrings

(76)
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Intramolecular Analog
HOCH2CH2CH2CH2CH2OH
via
130
H2SO4
(76)
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15.8Esterification
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Esterification
H


ROH
H2O

• condensation
• Fischer esterification
• acid catalyzed
• reversible

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Example of Fischer Esterification
0.1 mol
0.6 mol

H2O

• 70 yield based on benzoic acid

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Reaction of Alcohols with Acyl Chlorides


ROH
HCl

• high yields
• not reversible when carried outin presence of
  pyridine

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Example

pyridine
(63)
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Reaction of Alcohols with Acid Anhydrides


ROH

• analogous to reaction with acyl chlorides

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Example
pyridine
(83)
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15.9Esters of Inorganic Acids
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Esters of Inorganic Acids
ROH HOEWG
ROEWG H2O
EWG is an electron-withdrawing group

HONO2
(HO)2SO2
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Esters of Inorganic Acids
ROH HOEWG
ROEWG H2O
EWG is an electron-withdrawing group

HONO2
(HO)2SO2
CH3OH HONO2
CH3ONO2 H2O
(66-80)
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15.10Oxidation of Alcohols
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Oxidation of Alcohols
Primary alcohols
RCH2OH
RCH
RCOH
Secondary alcohols
from H2O
RCR'
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Typical Oxidizing Agents

• Aqueous solution
• Mn(VII) Cr(VI)
• KMnO4 H2CrO4
• H2Cr2O7

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Aqueous Cr(VI)
FCH2CH2CH2CH2OH
H2SO4
K2Cr2O7
H2O
FCH2CH2CH2COH
(74)
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Aqueous Cr(VI)
FCH2CH2CH2CH2OH
H2SO4
K2Cr2O7
H2SO4
H2O
Na2Cr2O7
H2O
FCH2CH2CH2COH
(74)
(85)
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Nonaqueous Sources of Cr(VI)

• All are used in CH2Cl2
• Pyridinium dichromate (PDC)
• (C5H5NH)2 Cr2O72
• Pyridinium chlorochromate (PCC)
• C5H5NH ClCrO3

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Example Oxidation of a primary alcohol with PCC
ClCrO3
PCC
CH3(CH2)5CH2OH
CH2Cl2
(78)
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Example Oxidation of a primary alcohol with PDC
PDC
CH2Cl2
(94)
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Mechanism
H
H
C
C
HOCrOH
CrOH
OH
O

• involves formation and elimination of a chromate
  ester

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Mechanism
H
H
C
C
HOCrOH
CrOH
OH
O

• involves formation and elimination of a chromate
  ester

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15.11Biological Oxidation of Alcohols
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Enzyme-catalyzed

CH3CH2OH
alcohol dehydrogenase


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Figure 15.3 Structure of NAD

• nicotinamide adenine dinucleotide (oxidized form)

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Enzyme-catalyzed

CH3CH2OH

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Enzyme-catalyzed
H
H

N
R
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15.12Oxidative Cleavage of Vicinal Diols
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Cleavage of Vicinal Diols by Periodic Acid

C
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Cleavage of Vicinal Diols by Periodic Acid
HIO4

(83)
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Cyclic Diols are Cleaved
HIO4