Lecture 17 - Alcohols, Phenols
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General
Organic Chemistry Two credits Second Semester 2009
King Saud bin Abdulaziz University for Health Science
Reference Book: Organic Chemistry: A Brief Course, by Robert C. Atkins and Francis A. Carey Third Edition
Instructor: Rabih O. Al-Kaysi, PhD.
Lecture 17
Chapter 10 Alcohols, Ethers and Phenols
Phenols
Dr. Wolf's CHM 201 & 202
24 - 3
Nomenclature
Dr. Wolf's CHM 201 & 202
24 - 4
Nomenclature OH CH3 5-Chloro-2-methylphenol Cl named on basis of phenol as parent substituents listed in alphabetical order lowest numerical sequence: first point of difference rule Dr. Wolf's CHM 201 & 202
24 - 5
Nomenclature OH
OH
OH
OH OH OH 1,2-Benzenediol (common name: pyrocatechol) Dr. Wolf's CHM 201 & 202
1,3-Benzenediol (common name: resorcinol)
1,4-Benzenediol (common name: hydroquinone) 24 - 6
Nomenclature OH p-Hydroxybenzoic acid CO2H name on basis of benzoic acid as parent higher oxidation states of carbon outrank hydroxyl group Dr. Wolf's CHM 201 & 202
24 - 7
Structure and Bonding
Dr. Wolf's CHM 201 & 202
24 - 8
Structure of Phenol
phenol is planar C—O bond distance is 136 pm, which is slightly shorter than that of CH3OH (142 pm) Dr. Wolf's CHM 201 & 202
24 - 9
Physical Properties
The OH group of phenols allows hydrogen bonding to other phenol molecules and to water.
Dr. Wolf's CHM 201 & 202
24 - 10
Hydrogen Bonding in Phenols O H
Dr. Wolf's CHM 201 & 202
O
24 - 11
Physical Properties
Compared to compounds of similar size and molecular weight, hydrogen bonding in phenol raises its melting point, boiling point, and solubility in water.
Dr. Wolf's CHM 201 & 202
24 - 12
Physical Properties C6H5CH3
C6H5OH
C6H5F
Molecular weight
92
94
96
Melting point (°C)
–95
43
–41
Boiling point (°C,1 atm)
111
132
85
Solubility in 0.05 8.2 0.2 H2O (g/100 mL,25°C) Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 13
Acidity of Phenols most characteristic property of phenols is their acidity
Dr. Wolf's CHM 201 & 202
24 - 14
Compare ••O••
– ••O•• ••
H Ka = 10-10
••
CH3CH2O
••
Dr. Wolf's CHM 201 & 202
+ + H
Ka = 10-16 H
+ + H
•••– CH3CH2O • ••
24 - 15
Delocalized negative charge in phenoxide ion
– •• ••O •• H
H
H
H H
Dr. Wolf's CHM 201 & 202
24 - 16
Delocalized negative charge in phenoxide ion
– •• ••O •• H
••O••
H
H
H H
Dr. Wolf's CHM 201 & 202
H
–H
••
H
H H
24 - 17
Delocalized negative charge in phenoxide ion
••O••
H
–H
••
H
H H
Dr. Wolf's CHM 201 & 202
24 - 18
Delocalized negative charge in phenoxide ion
••O••
H
••O••
H ••
H
– H
H
Dr. Wolf's CHM 201 & 202
H
–H
••
H
H H
24 - 19
Delocalized negative charge in phenoxide ion
••O••
H
H ••
H
– H
H
Dr. Wolf's CHM 201 & 202
24 - 20
Delocalized negative charge in phenoxide ion
••O••
H
H
H
– H
H
••
H H
Dr. Wolf's CHM 201 & 202
••O••
–
••
H H
H
24 - 21
Phenols are converted to phenoxide ions in aqueous base ••O••
– ••O•• ••
H – + HO
stronger acid
Dr. Wolf's CHM 201 & 202
+ H2O weaker acid
24 - 22
Substituent Effects on the Acidity of Phenols
Dr. Wolf's CHM 201 & 202
24 - 23
Electron-releasing groups have little or no effect OH
Ka:
1 x 10-10
Dr. Wolf's CHM 201 & 202
OH
OH
CH3
OCH3
5 x 10-11
6 x 10-11
24 - 24
Electron-withdrawing groups increase acidity OH
Ka:
1 x 10-10
Dr. Wolf's CHM 201 & 202
OH
OH
Cl
NO2
4 x 10-9
7 x 10-8
24 - 25
Effect of electron-withdrawing groups is most pronounced at ortho and para positions
OH
OH
OH NO2 NO2
NO2 Ka:
6 x 10-8
Dr. Wolf's CHM 201 & 202
4 x 10-9
7 x 10-8 24 - 26
Effect of strong electron-withdrawing groups is cumulative OH
OH
OH NO2
NO2 Ka: 7 x 10-8 Dr. Wolf's CHM 201 & 202
NO2
O2N
NO2
NO2
1 x 10-4
4 x 10-1 24 - 27
Resonance Depiction – •• ••O ••
••O••••
H
H
H
H
H
H
H
H
••O ••
N
+
••• O• •• –
N •• ••O + – ••
••• O• •• –
Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 28
Sources of Phenols Phenol is an important industrial chemical. Major use is in phenolic resins for adhesives and plastics. Annual U.S. production is about 4 billion pounds per year.
Dr. Wolf's CHM 201 & 202
24 - 29
Industrial Preparations of Phenol
SO3H
Cl
1. NaOH 2. H+ heat 1. NaOH heat 2. H
+
OH
CH(CH3)2 1. O2 2. H2O H2SO4
Just for general knowledge, will not be tested on
Dr. Wolf's CHM 201 & 202
24 - 30
Laboratory Synthesis of Phenols from arylamines via diazonium ions
O2N NH2
1. NaNO2, H2SO4, H2O
O2N OH
2. H2O, heat (81-86%)
Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 31
Naturally Occurring Phenols Many phenols occur naturally
Dr. Wolf's CHM 201 & 202
24 - 32
Example: Thymol
OH CH3
CH(CH3)2
Thymol (major constituent of oil of thyme)
Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 33
Example: 2,5-Dichlorophenol
OH Cl
Cl
2,5-Dichlorophenol (from defensive secretion of a species of grasshopper) Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 34
Reactions of Phenols: Electrophilic Aromatic Substitution Hydroxyl group strongly activates the ring toward electrophilic aromatic substitution
Dr. Wolf's CHM 201 & 202
24 - 35
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 36
Halogenation OH
OH + Br2
ClCH2CH2Cl 0°C Br (93%)
monohalogenation in nonpolar solvent (1,2-dichloroethane) Dr. Wolf's CHM 201 & 202
24 - 37
Halogenation OH
OH + 3Br2 F
H2O
Br
Br
25°C
F Br (95%)
multiple halogenation in polar solvent (water) Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 38
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 39
Nitration OH
OH NO2
HNO3 acetic acid 5°C CH3 OH group controls regiochemistry Dr. Wolf's CHM 201 & 202
CH3 (73-77%)
24 - 40
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 41
Nitrosation NO OH
OH
NaNO2
H2SO4, H2O 0°C only strongly activated rings undergo nitrosation when treated with nitrous acid
(99%)
Just for general knowledge, will not be tested on
Dr. Wolf's CHM 201 & 202
24 - 42
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 43
Sulfonation
OH H3C
OH CH3
H2SO4
H3C
CH3
100°C SO3H OH group controls regiochemistry Dr. Wolf's CHM 201 & 202
(69%) 24 - 44
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 45
Friedel-Crafts Alkylation OH
OH CH3
CH3
(CH3)3COH H3PO4 60°C H3C
(CH3)3COH reacts with H3PO4 to give (CH3)3C+ Dr. Wolf's CHM 201 & 202
C CH3 CH3 (63%) 24 - 46
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 47
Organic Chemistry Two credits Second Semester 2009
King Saud bin Abdulaziz University for Health Science
Reference Book: Organic Chemistry: A Brief Course, by Robert C. Atkins and Francis A. Carey Third Edition
Instructor: Rabih O. Al-Kaysi, PhD.
Lecture 17
Chapter 10 Alcohols, Ethers and Phenols
Phenols
Dr. Wolf's CHM 201 & 202
24 - 3
Nomenclature
Dr. Wolf's CHM 201 & 202
24 - 4
Nomenclature OH CH3 5-Chloro-2-methylphenol Cl named on basis of phenol as parent substituents listed in alphabetical order lowest numerical sequence: first point of difference rule Dr. Wolf's CHM 201 & 202
24 - 5
Nomenclature OH
OH
OH
OH OH OH 1,2-Benzenediol (common name: pyrocatechol) Dr. Wolf's CHM 201 & 202
1,3-Benzenediol (common name: resorcinol)
1,4-Benzenediol (common name: hydroquinone) 24 - 6
Nomenclature OH p-Hydroxybenzoic acid CO2H name on basis of benzoic acid as parent higher oxidation states of carbon outrank hydroxyl group Dr. Wolf's CHM 201 & 202
24 - 7
Structure and Bonding
Dr. Wolf's CHM 201 & 202
24 - 8
Structure of Phenol
phenol is planar C—O bond distance is 136 pm, which is slightly shorter than that of CH3OH (142 pm) Dr. Wolf's CHM 201 & 202
24 - 9
Physical Properties
The OH group of phenols allows hydrogen bonding to other phenol molecules and to water.
Dr. Wolf's CHM 201 & 202
24 - 10
Hydrogen Bonding in Phenols O H
Dr. Wolf's CHM 201 & 202
O
24 - 11
Physical Properties
Compared to compounds of similar size and molecular weight, hydrogen bonding in phenol raises its melting point, boiling point, and solubility in water.
Dr. Wolf's CHM 201 & 202
24 - 12
Physical Properties C6H5CH3
C6H5OH
C6H5F
Molecular weight
92
94
96
Melting point (°C)
–95
43
–41
Boiling point (°C,1 atm)
111
132
85
Solubility in 0.05 8.2 0.2 H2O (g/100 mL,25°C) Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 13
Acidity of Phenols most characteristic property of phenols is their acidity
Dr. Wolf's CHM 201 & 202
24 - 14
Compare ••O••
– ••O•• ••
H Ka = 10-10
••
CH3CH2O
••
Dr. Wolf's CHM 201 & 202
+ + H
Ka = 10-16 H
+ + H
•••– CH3CH2O • ••
24 - 15
Delocalized negative charge in phenoxide ion
– •• ••O •• H
H
H
H H
Dr. Wolf's CHM 201 & 202
24 - 16
Delocalized negative charge in phenoxide ion
– •• ••O •• H
••O••
H
H
H H
Dr. Wolf's CHM 201 & 202
H
–H
••
H
H H
24 - 17
Delocalized negative charge in phenoxide ion
••O••
H
–H
••
H
H H
Dr. Wolf's CHM 201 & 202
24 - 18
Delocalized negative charge in phenoxide ion
••O••
H
••O••
H ••
H
– H
H
Dr. Wolf's CHM 201 & 202
H
–H
••
H
H H
24 - 19
Delocalized negative charge in phenoxide ion
••O••
H
H ••
H
– H
H
Dr. Wolf's CHM 201 & 202
24 - 20
Delocalized negative charge in phenoxide ion
••O••
H
H
H
– H
H
••
H H
Dr. Wolf's CHM 201 & 202
••O••
–
••
H H
H
24 - 21
Phenols are converted to phenoxide ions in aqueous base ••O••
– ••O•• ••
H – + HO
stronger acid
Dr. Wolf's CHM 201 & 202
+ H2O weaker acid
24 - 22
Substituent Effects on the Acidity of Phenols
Dr. Wolf's CHM 201 & 202
24 - 23
Electron-releasing groups have little or no effect OH
Ka:
1 x 10-10
Dr. Wolf's CHM 201 & 202
OH
OH
CH3
OCH3
5 x 10-11
6 x 10-11
24 - 24
Electron-withdrawing groups increase acidity OH
Ka:
1 x 10-10
Dr. Wolf's CHM 201 & 202
OH
OH
Cl
NO2
4 x 10-9
7 x 10-8
24 - 25
Effect of electron-withdrawing groups is most pronounced at ortho and para positions
OH
OH
OH NO2 NO2
NO2 Ka:
6 x 10-8
Dr. Wolf's CHM 201 & 202
4 x 10-9
7 x 10-8 24 - 26
Effect of strong electron-withdrawing groups is cumulative OH
OH
OH NO2
NO2 Ka: 7 x 10-8 Dr. Wolf's CHM 201 & 202
NO2
O2N
NO2
NO2
1 x 10-4
4 x 10-1 24 - 27
Resonance Depiction – •• ••O ••
••O••••
H
H
H
H
H
H
H
H
••O ••
N
+
••• O• •• –
N •• ••O + – ••
••• O• •• –
Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 28
Sources of Phenols Phenol is an important industrial chemical. Major use is in phenolic resins for adhesives and plastics. Annual U.S. production is about 4 billion pounds per year.
Dr. Wolf's CHM 201 & 202
24 - 29
Industrial Preparations of Phenol
SO3H
Cl
1. NaOH 2. H+ heat 1. NaOH heat 2. H
+
OH
CH(CH3)2 1. O2 2. H2O H2SO4
Just for general knowledge, will not be tested on
Dr. Wolf's CHM 201 & 202
24 - 30
Laboratory Synthesis of Phenols from arylamines via diazonium ions
O2N NH2
1. NaNO2, H2SO4, H2O
O2N OH
2. H2O, heat (81-86%)
Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 31
Naturally Occurring Phenols Many phenols occur naturally
Dr. Wolf's CHM 201 & 202
24 - 32
Example: Thymol
OH CH3
CH(CH3)2
Thymol (major constituent of oil of thyme)
Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 33
Example: 2,5-Dichlorophenol
OH Cl
Cl
2,5-Dichlorophenol (from defensive secretion of a species of grasshopper) Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 34
Reactions of Phenols: Electrophilic Aromatic Substitution Hydroxyl group strongly activates the ring toward electrophilic aromatic substitution
Dr. Wolf's CHM 201 & 202
24 - 35
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 36
Halogenation OH
OH + Br2
ClCH2CH2Cl 0°C Br (93%)
monohalogenation in nonpolar solvent (1,2-dichloroethane) Dr. Wolf's CHM 201 & 202
24 - 37
Halogenation OH
OH + 3Br2 F
H2O
Br
Br
25°C
F Br (95%)
multiple halogenation in polar solvent (water) Just for general knowledge, will not be tested on Dr. Wolf's CHM 201 & 202
24 - 38
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 39
Nitration OH
OH NO2
HNO3 acetic acid 5°C CH3 OH group controls regiochemistry Dr. Wolf's CHM 201 & 202
CH3 (73-77%)
24 - 40
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 41
Nitrosation NO OH
OH
NaNO2
H2SO4, H2O 0°C only strongly activated rings undergo nitrosation when treated with nitrous acid
(99%)
Just for general knowledge, will not be tested on
Dr. Wolf's CHM 201 & 202
24 - 42
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 43
Sulfonation
OH H3C
OH CH3
H2SO4
H3C
CH3
100°C SO3H OH group controls regiochemistry Dr. Wolf's CHM 201 & 202
(69%) 24 - 44
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 45
Friedel-Crafts Alkylation OH
OH CH3
CH3
(CH3)3COH H3PO4 60°C H3C
(CH3)3COH reacts with H3PO4 to give (CH3)3C+ Dr. Wolf's CHM 201 & 202
C CH3 CH3 (63%) 24 - 46
Electrophilic Aromatic Substitution in Phenols Halogenation Nitration Nitrosation Sulfonation Friedel-Crafts Alkylation Friedel-Crafts Acylation
Dr. Wolf's CHM 201 & 202
24 - 47
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