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Transcript of Chapter 15 Alcohols, Diols, and Thiols Copyright The McGraw-Hill Companies, Inc. Permission...
![Page 1: Chapter 15 Alcohols, Diols, and Thiols Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.](https://reader036.fdocuments.us/reader036/viewer/2022062311/5a4d1b8e7f8b9ab0599c0000/html5/thumbnails/1.jpg)
Chapter 15Chapter 15Alcohols, Diols, and ThiolsAlcohols, Diols, and Thiols
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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15.115.1Sources of AlcoholsSources of Alcohols
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Methanol is an industrial chemical.
End uses: solvent, antifreeze, fuel.
Principal use: preparation of formaldehyde.
Prepared by hydrogenation of carbon monoxide.
CO + 2H2 CH3OH
Methanol
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Ethanol is an industrial chemical.
Most ethanol comes from fermentation.
Synthetic ethanol is produced by hydrationof ethylene.
Synthetic ethanol is denatured (madeunfit for drinking) by adding methanol, benzene,pyridine, castor oil, gasoline, etc.
Ethanol
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Isopropyl alcohol is prepared by hydration of propene.
All alcohols with four carbons or fewer are readily available.
Most alcohols with five or six carbons are readily available.
Other Alcohols
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Hydration of alkenes
Hydroboration-oxidation of alkenes
Hydrolysis of alkyl halides
Syntheses using Grignard reagentsOrganolithium reagents
Sources of Alcohols
Reactions discussed in earlier chapters (Table 15.1)
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Reduction of aldehydes and ketones
Reduction of carboxylic acids
Reaction of Grignard reagents with epoxides
Diols by hydroxylation of alkenes
Sources of Alcohols
New methods in Chapter 15
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15.215.2Preparation of AlcoholsPreparation of Alcohols
bybyReduction of Aldehydes and KetonesReduction of Aldehydes and Ketones
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C
R
H OH
H
C
R
H
O
Reduction of Aldehydes Gives Primary Alcohols
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Pt, ethanol
(92%)
Example: Catalytic Hydrogenation CH3O CH2OH
O
CH3O CH + H2
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C
R
H OH
R'
C
R
R'
O
Reduction of Ketones Gives Secondary Alcohols
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(93-95%)
Example: Catalytic Hydrogenation
+ H2
O Pt
ethanol
H OH
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H:–C
R
H OH
H
C
R
H
O
H:–C
R
H OH
R'
C
R
R'
O
Retrosynthetic Analysis
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Sodiumborohydride
Na+ –
B
H
H
HH
Lithiumaluminum hydride
Li+ –
Al
H
H
HH
Metal Hydride Reducing Agents
act as hydride donors
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Examples: Sodium Borohydride
O
CH
O2N O NaBH4
methanol
(82%)
CH2OH
O2N H OH
(84%)
NaBH4
ethanol
Aldehyde
Ketone
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Lithium Aluminum Hydride
More reactive than sodium borohydride.
Cannot use water, ethanol, methanol etc.as solvents.
Diethyl ether is most commonly used solvent.
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Examples: Lithium Aluminum Hydride
Aldehyde
Ketone
O
CH3(CH2)5CH
1. LiAlH4
diethyl ether2. H2O
O
(C6H5)2CHCCH3
1. LiAlH4
diethyl ether2. H2O
(84%)
CH3(CH2)5CH2OH
(86%)
OH
(C6H5)2CHCHCH3
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Neither NaBH4 or LiAlH4reduces carbon-carbondouble bonds.
O
H OH
1. LiAlH4
diethyl ether2. H2O
(90%)
Selectivity
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15.315.3Preparation of Alcohols By ReductionPreparation of Alcohols By Reduction
of Carboxylic Acidsof Carboxylic Acids
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lithium aluminum hydride is only effective reducing agent
Reduction of Carboxylic AcidsGives Primary Alcohols
C
R
H OH
H
C
R
HO
O
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Example: Reduction of a Carboxylic Acid
1. LiAlH4
diethyl ether2. H2O
COH
O CH2OH
(78%)
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15.415.4Preparation of Alcohols From EpoxidesPreparation of Alcohols From Epoxides
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Reaction of Grignard Reagentswith Epoxides
H2C CH2
O
R MgX
CH2 CH2 OMgX
R
H3O+
RCH2CH2OH
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CH3(CH2)4CH2MgBr H2C CH2
O
+
1. diethyl ether2. H3O+
CH3(CH2)4CH2CH2CH2OH
(71%)
Example
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15.515.5Preparation of DiolsPreparation of Diols
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Diols are Prepared by...
Reactions used to prepare alcohols
Hydroxylation of alkenes
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O O
HCCH2CHCH2CH
CH3
H2 (100 atm)
Ni, 125°C
HOCH2CH2CHCH2CH2OH
CH3
3-Methyl-1,5-pentanediol
(81-83%)
Example: Reduction of a Dialdehyde
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Vicinal diols have hydroxyl groups on adjacent carbons.
Ethylene glycol (HOCH2CH2OH) is most familiar example.
Hydroxylation of AlkenesGives Vicinal Diols
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Osmium Tetraoxide is Key Reagent
C CHO OH
C C
OsO4O O
Os
OO
CC
Cyclic osmate ester
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(CH3)3COOHOsO4 (cat)
tert-Butyl alcoholHO–
Example
(73%)
CH2CH3(CH2)7CH
CH3(CH2)7CHCH2OH
OH
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Example H
H
(CH3)3COOHOsO4 (cat)
tert-Butyl alcoholHO–
(62%)
H
H
OHHO
Stereospecificsyn addition of —OH groups to each carbonof double bond