Download Organic Chemistry II Introduction

Organic Chemistry II
Alcohols, Phenols, Thiols
5/12/2017
Dr Seemal Jelani
Chem-240
1
Chapter Objectives
• Nomenclature
• Properties
• Preparation
• Reaction
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Alcohols and Phenols
• Important solvents and intermediates
• Phenols contain an OH group
connected to a carbon in a benzene
ring
• Methanol, CH3OH, common name is
methyl alcohol, a solvent, a fuel
additive, produced in large quantities
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• Ethanol, CH3CH2OH, common
name is ethyl alcohol, a solvent,
fuel, beverage, produced in large
quantities
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Alcohols, Phenols, Thiols, Ethers
• Considered derivatives of water
OH
SH
OH
alcohol
thiol
phenol
O
thiophenol
S
ether
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SH
sulfide
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Nomenclature of Alcohols
• Derivatives of alkane with –ol suffix
• Name longest chain containing OH
• Number the chain starting nearest
the carbon bearing the OH group
• Number substituents, name, and list
alphabetically
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Examples
propanol
OH
OH
trans-1,2-cyclopentanediol
OH
OH
3-ethylheptan-3-ol
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Classification of Alcohols
• Primary – OH is attached to a carbon
bearing one carbon atom
• Secondary – OH is attached to a
carbon bearing two carbon atoms
• Tertiary – OH is attached to a carbon
bearing three carbon atoms
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Examples
OH
primary alcohol
secondary alcohol
OH
tertiary alcohol
OH
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Common Names
OH
OH
OH
benzyl alcohol
OH
allyl alcohol
HO
HO
OH
OH
glycerol
ethylene glycol
t-butyl alcohol
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Phenols
• Common natural source – coal tar
• Found in many plants
OH
OH
CO2CH3
oil of wintergreen
OH
coal tar
OH
OH
CO2H
R
willow bark
bioactive ingredient
poison ivy and oak
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Phenols
OH
OH
OMe
OMe
eugenol (oil of clove)
isoeugenol (oil of nutmeg)
OH
OMe
OH
O
O
C5H11
tetrahydrocannabinol
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vanillin
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Nomenclature of Phenols
• Use “phene” (the French name for benzene) as
•
the parent hydrocarbon name, not benzene
Name substituents on aromatic ring by their
position from OH
OH
OH
H3C
p-methylphenol
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OH
Cl
o-chlorophenol
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O2N
NO2
2,4-dinitrophenol
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Common Names
• Many common names in use
OH
OH
OH
H3C
CH3
CH3
o-cresol
p-cresol
m-cresol
OH
OH
OH
HO
OH
OH
catechol
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hydroquinone
resorcinol
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Nomenclature of Thiols
• Same naming system as alcohols
• Suffix is –thiol
• Sometimes named as mercaptans
SH
SH
CH3
isopropyl thiol
cis-2-methylcycloheptane thiol
OH
SH
m-mercaptophenol
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Biosynthesis of Ethanol
(Fermentation)
O
OH
H3C
C6H12O6
O
glucose
pyruvate
O
OH
H3C
CH3CH2OH
O
pyruvate
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Properties
• Alcohols and phenols are similar to water form
•
•
•
•
•
strong H-bonds
Giving higher boiling points than the
corresponding hydrocarbon
Thiols do not form H-bonds (EN of S is low)
Alcohols and phenols are weakly basic
Alcohols and phenols are weakly acidic
Phenols and Thiols are more acidic than water
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Acidity Constants
OH
CH3CH2OH
H2O
pKa = 18
pKa = 16
pKa = 15.7
CH3OH
pKa = 15.5
pKa = 10.3
CH3SH
OH
pKa = 10.2
H3C
OH
pKa = 9.9
OH
pKa = 7.2
decreasing acidity
O2N
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Acidity of Alcohols
• Do not react with amines or
NaHCO3
• Limited reactivity with NaOH
• React with alkali metals Na, K
• React with strong bases like NaH
or NaNH2 or RLi and RMgBr
• Forms the alkoxide (RO-1)
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Reactions with Bases
ROH + NH3
No Reaction
ROH + NaHCO3
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No Reaction
ROH + NaOH
RO- + H2O
ROH + NaH
RO- + H2
ROH + Na
RO- + H2
ROH + RLi
RO- + RH
ROH + RMgX
RO- + RH
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Acidity of Phenols
•
•
•
•
•
ArOH is more acidic than ROH
Soluble in dilute NaOH
Anion is resonance stabilized
EWG make phenols more acidic than phenol
EDG make phenols less acidic than phenol
O
O
OH
-
NaOH
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Alcohols an Overview
• Alcohols are derived from many types of
•
•
•
•
compounds
Alkenes, alkyl halides, ketones, esters,
aldehydes, and carboxylic acids can provide the
alcohol
Alcohols are among most common natural
materials
The alcohol hydroxyl can be converted to many
other functional groups
This makes alcohols useful in synthetic planning
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Preparation
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Preparation of Alcohols
• Hydration of Alkenes
• BH3/THF followed by H2O2 in
NaOH
• Hg(OAc)2 followed by NaBH4
• OsO4 followed by NaHSO3 (cis1,2-diols)
• RCO3H followed by aqueous acid
(trans-1,2-diols)
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• From Aldehydes and Ketones
• Reduction with NaBH4
– Reduces alpha beta unsaturated carbonyls as well
Reduction with LiAlH4
– Doesn’t touch alpha beta unsaturated carbonyls
• From Esters
– Reduction with LiAlH4 (LAH)
– No reaction with NaBH4
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Reduction of Ketones
OH
OH
NaBH4
O
+
OH
LAH
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Preparation of Alcohols
• From carboxylic acids
– Reduction with LiAlH4 is slow
– Reduction with NaBH4 doesn’t occur
– Reduction with BH3 is preferred method
LiAlH4
RCO2H
RCH2OH
slow
NaBH4
No Reaction
RCO2H
BH3
RCO2H
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RCH2OH
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From Alkyl halides
• RX + Mg provides the Grignard
reagent
• Grignard reagents react with
carbonyls to provide the alcohols
CH3Br + Mg
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CH3-Mg-Br
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Grignard Reactions
• With aldehydes or
O
OH
1. CH3MgBr
ketones
2. H3O+
O
CH3
OH
1. CH3MgBr
H
H
• With esters
2. H3O+
1. CH3MgBr
O
CH3
OH
CH3
OMe
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2. H3O+
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CH3
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Grignard Reactions
• With carboxylic acids
• Grignard's are strong bases
• React with the acidic proton
O
1. CH3MgBr
OH
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O
2.
OH
H3O+
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+ CH4
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Reactions
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Reactions of Alcohols
• Alcohols react at
– the O-H bond
– the C-O bond
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Alcohols to Alkyl Halides
tertiary alcohols
HCl
Cl
OH
HBr
Br
OH
primary or secondary alcohols
SOCl2
OH
OH
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Cl
PBr3
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Cl
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Alcohols to Alkenes
•
•
•
•
Dehydration
Acid catalyzed reaction
Excellent reaction for tertiary alcohols (E1)
Provides the Zaitsev product
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• When the substrate is
asymmetric, regioselectivity is
determined by Zaitsev’s rule
• The one -step mechanisms is E2
reaction and two step reaction
mechanism is called E1 reaction,
respectively.
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What is regioselectivity
•It is the preference of one
direction of chemical bond
making or breaking over all
other possible directions
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What is Zaitsev’s rule
• In chemistry, Zaitsev's rule, Saytzeff's
rule or Saytsev's rule is a rule that
states
“that if more than one alkene can be
formed during dehalogenation by an
elimination reaction the more stable
alkene is the major product”
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Who is then stable
• In general, the compound that
has a more highly substituted
C=C double bond is more
stable.
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Alcohol to Alkene
• Milder reaction developed
• E2 process
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Alcohols to Esters
•
•
•
•
Alcohols react with carboxylic acids
Reaction is acid catalyzed
Alcohols react with acid chlorides
Reaction is base catalyzed
O
R
ROH/H+
OH
H3O+
O
R
OR
SOCl2
O
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R
O
ROH/pyridine
Cl
R
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OR
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Alcohols to Tosylate Esters
• Reaction with p-toluenesulfonyl chloride (tosyl
•
•
chloride, p-TosCl) in pyridine yields alkyl
tosylates, ROTos
Formation of the tosylate does not involve the
C–O bond so configuration at a chirality center is
maintained
Alkyl tosylates react like alkyl halides
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Oxidation of Alcohols
• Can be accomplished by inorganic reagents, such
as KMnO4, CrO3, and Na2Cr2O7 or by more
selective, expensive reagents
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Oxidation of Primary Alcohols
• To aldehyde: pyridinium chlorochromate
(PCC = C5H6NCrO3Cl) in dichloromethane
• Other reagents produce carboxylic acids
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Oxidation of Secondary Alcohols
• Effective with inexpensive reagents such as
•
Na2Cr2O7 in acetic acid
PCC is used for sensitive alcohols at lower
temperatures
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Preparation and Uses of Phenols
• Industrial process from readily available cumene
• Forms cumene hydroperoxide with oxygen at
•
high temperature
Converted into phenol and acetone by acid
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Industrial Preparation of Phenol
Cl
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NaOH/heat
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OH
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Laboratory Preparation of Phenols
• From aromatic sulfonic acids by melting with
•
NaOH at high temperature
Limited to the preparation of alkyl-substituted
phenols
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Reactions of Phenols
• The hydroxyl group is a strongly activating,
•
•
making phenols substrates for electrophilic
halogenation, nitration, sulfonation, and Friedel–
Crafts reactions
Reaction of a phenol with strong oxidizing
agents yields a quinone
Fremy's salt [(KSO3)2NO] works under mild
conditions through a radical mechanism
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