dr. wolf's chm 201 & 20222 - 1 chapter 22 phenols

Dr. Wolf's CHM 201 & 202 22 - 1

Chapter 22Chapter 22PhenolsPhenols

Chapter 22Chapter 22PhenolsPhenols

Dr. Wolf's CHM 201 & 202 22 - 2

NomenclatureNomenclatureNomenclatureNomenclature

Dr. Wolf's CHM 201 & 202 22 - 3

named on basis of phenol as parentnamed on basis of phenol as parent

substituents listed in alphabetical ordersubstituents listed in alphabetical order

lowest numerical sequence: first point oflowest numerical sequence: first point ofdifference ruledifference rule

5-5-ChloroChloro-2--2-methylmethylphenolphenol

NomenclatureNomenclatureNomenclatureNomenclature OHOH

CHCH33

ClCl

Dr. Wolf's CHM 201 & 202 22 - 4

NomenclatureNomenclatureNomenclatureNomenclature OHOH

OHOH

1,2-Benzenediol1,2-Benzenediol

OHOH

OHOH

OHOH

OHOH

1,3-Benzenediol1,3-Benzenediol 1,4-Benzenediol1,4-Benzenediol

(common name:(common name:pyrocatechol)pyrocatechol)

(common name:(common name:resorcinol)resorcinol)

(common name:(common name:hydroquinone)hydroquinone)

Dr. Wolf's CHM 201 & 202 22 - 5

name on basis of benzoic acid as parentname on basis of benzoic acid as parent

higher oxidation states of carbon outrankhigher oxidation states of carbon outrankhydroxylhydroxyl group group

NomenclatureNomenclatureNomenclatureNomenclature

pp-Hydroxybenzoic acid-Hydroxybenzoic acid

OHOH

COCO22HH

Dr. Wolf's CHM 201 & 202 22 - 6

Structure and BondingStructure and BondingStructure and BondingStructure and Bonding

Dr. Wolf's CHM 201 & 202 22 - 7

phenol is planarphenol is planar

C—O bond distance is 136 pm, which isC—O bond distance is 136 pm, which isslightly shorter than that of CHslightly shorter than that of CH33OH (142 pm)OH (142 pm)

Structure of PhenolStructure of PhenolStructure of PhenolStructure of Phenol

Dr. Wolf's CHM 201 & 202 22 - 8

The OH group of phenols allows hydrogen bondingThe OH group of phenols allows hydrogen bondingto other phenol molecules and to water.to other phenol molecules and to water.

Physical PropertiesPhysical PropertiesPhysical PropertiesPhysical Properties

Dr. Wolf's CHM 201 & 202 22 - 9

HH OOOO

Hydrogen Bonding in PhenolsHydrogen Bonding in PhenolsHydrogen Bonding in PhenolsHydrogen Bonding in Phenols

Dr. Wolf's CHM 201 & 202 22 - 10

Compared to compounds of similar size andCompared to compounds of similar size andmolecular weight, hydrogen bonding in phenol molecular weight, hydrogen bonding in phenol raises its melting point, boiling point, andraises its melting point, boiling point, andsolubility in water.solubility in water.

Physical Properties (Table 24.1)Physical Properties (Table 24.1)Physical Properties (Table 24.1)Physical Properties (Table 24.1)

Dr. Wolf's CHM 201 & 202 22 - 11

Physical Properties (Table 24.1)Physical Properties (Table 24.1)Physical Properties (Table 24.1)Physical Properties (Table 24.1)

CC66HH55CHCH33 CC66HH55OHOH CC66HH55FF

Molecular weightMolecular weight 9292 9494 9696

––9595 4343 ––4141Melting point (°C)Melting point (°C)

BoilingBoilingpoint (°C,1 atm)point (°C,1 atm)

111111 132132 8585

Solubility inSolubility inHH22O (g/100 mL,25°C)O (g/100 mL,25°C)

0.050.05 8.28.2 0.20.2

Dr. Wolf's CHM 201 & 202 22 - 12

Acidity of PhenolsAcidity of Phenols

most characteristic property of most characteristic property of phenols is their acidityphenols is their acidity

Dr. Wolf's CHM 201 & 202 22 - 13

CompareCompareCompareCompare OO HH••••••••

KKaa = 10 = 10-10-10

++HH ++

OO•••••••• ••••

––

CHCH33CHCH22OO HH••••

••••

KKaa = 10 = 10-16-16

++HH ++ CHCH33CHCH22OO••••

••••

––••••

Dr. Wolf's CHM 201 & 202 22 - 14

Delocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ion

••••OO••••

HH

HH

HH

HH

HH

••••––

Dr. Wolf's CHM 201 & 202 22 - 15


••••OO••••

HH

HH

HH

HH

HH

••••–– ••••OO

••••

HH

HH

HH

HH

HH

––••••

Dr. Wolf's CHM 201 & 202 22 - 16

Delocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ionDelocalized negative charge in phenoxide ion ••••OO••••

HH

HH

HH

HH

HH

––••••

Dr. Wolf's CHM 201 & 202 22 - 17


HH

HH

HH

HH

HH

––•••• ••••OO

••••

HH

HH

HH

HH

HH––••••

Dr. Wolf's CHM 201 & 202 22 - 18


HH

HH

HH

HH

HH––••••

Dr. Wolf's CHM 201 & 202 22 - 19


••••OO••••

HH

HH

HH

HH

HH

––••••

••••OO••••

HH

HH

HH

HH

HH––••••

Dr. Wolf's CHM 201 & 202 22 - 20

Phenols are converted to phenoxide ionsPhenols are converted to phenoxide ionsin aqueous basein aqueous base

Phenols are converted to phenoxide ionsPhenols are converted to phenoxide ionsin aqueous basein aqueous base OO HH••••

•••• OO•••••••• ••••

––

++ HOHO–– ++ HH22OO

stronger acidstronger acid weaker acidweaker acid

Dr. Wolf's CHM 201 & 202 22 - 21

Substituent EffectsSubstituent Effectson theon the


Substituent EffectsSubstituent Effectson theon the


Dr. Wolf's CHM 201 & 202 22 - 22

Electron-releasing groups have little or no effectElectron-releasing groups have little or no effectElectron-releasing groups have little or no effectElectron-releasing groups have little or no effect OHOH

CHCH33

OHOH OHOH

OCHOCH33

KKaa:: 1 x 101 x 10-10-10 5 x 105 x 10-11-11 6 x 106 x 10-11-11

Dr. Wolf's CHM 201 & 202 22 - 23

Electron-withdrawing groups increase acidityElectron-withdrawing groups increase acidityElectron-withdrawing groups increase acidityElectron-withdrawing groups increase acidity OHOH

ClCl

OHOH OHOH

NONO22

KKaa:: 1 x 101 x 10-10-10 4 x 104 x 10-9-9 7 x 107 x 10-8-8

Dr. Wolf's CHM 201 & 202 22 - 24

Effect of electron-withdrawing groups is mostEffect of electron-withdrawing groups is mostpronounced at ortho and para positionspronounced at ortho and para positions

Effect of electron-withdrawing groups is mostEffect of electron-withdrawing groups is mostpronounced at ortho and para positionspronounced at ortho and para positions OHOH

NONO22

OHOH

NONO22

OHOH

NONO22

KKaa:: 6 x 106 x 10-8-8 4 x 104 x 10-9-9 7 x 107 x 10-8-8

Dr. Wolf's CHM 201 & 202 22 - 25

Effect of strong electron-withdrawing groupsEffect of strong electron-withdrawing groupsis cumulativeis cumulative

Effect of strong electron-withdrawing groupsEffect of strong electron-withdrawing groupsis cumulativeis cumulative OHOH

NONO22

OHOH

NONO22

NONO22

OHOH

NONO22

NONO22

OO22NN

KKaa:: 7 x 107 x 10-8-8 1 x 101 x 10-4-4 4 x 104 x 10-1-1

Dr. Wolf's CHM 201 & 202 22 - 26

Resonance DepictionResonance DepictionResonance DepictionResonance Depiction

••••OO••••

NN

HH

HH

HH

HH

••••OO OO

••••

••••

•••••••••••• ––

++

••••

––

••••OO••••

NN

HH

HH

HH

HH

••••

––

OO OO

••••

••••

•••••••••••• ––

++

Dr. Wolf's CHM 201 & 202 22 - 27

Sources of PhenolsSources of PhenolsSources of PhenolsSources of Phenols

Phenol is an important industrial chemical.Phenol is an important industrial chemical.

Major use is in phenolic resins for adhesives Major use is in phenolic resins for adhesives and plastics.and plastics.

Annual U.S. production is about 4 billion Annual U.S. production is about 4 billion pounds per year.pounds per year.

Dr. Wolf's CHM 201 & 202 22 - 28

1. NaOH 1. NaOH heat heat

2. H2. H++

1. NaOH 1. NaOH heat heat

2. H2. H++1. O1. O22

2. H2. H22OO

H H22SOSO44

IndustrialIndustrial

PreparationsPreparations

of Phenolof Phenol

IndustrialIndustrial

PreparationsPreparations

of Phenolof Phenol

SOSO33HH

ClCl

CH(CHCH(CH33))22

OHOH

Dr. Wolf's CHM 201 & 202 22 - 29

(81-86%)(81-86%)

OO22NN

NNHH22

OO22NN

OOHH

1.1. NaNONaNO22,,

HH22SOSO44,,

HH22OO

2.2. HH22O, heatO, heat

Laboratory Synthesis of PhenolsLaboratory Synthesis of PhenolsLaboratory Synthesis of PhenolsLaboratory Synthesis of Phenols

from arylamines via diazonium ionsfrom arylamines via diazonium ions

Dr. Wolf's CHM 201 & 202 22 - 30

Naturally Occurring PhenolsNaturally Occurring PhenolsNaturally Occurring PhenolsNaturally Occurring Phenols

Many phenols occur naturallyMany phenols occur naturally

Dr. Wolf's CHM 201 & 202 22 - 31

CH(CHCH(CH33))22

OHOH

CHCH33

ThymolThymol

(major constituent of oil of thyme)(major constituent of oil of thyme)

Example: ThymolExample: ThymolExample: ThymolExample: Thymol

Dr. Wolf's CHM 201 & 202 22 - 32

ClCl

OHOH

ClCl

2,5-Dichlorophenol2,5-Dichlorophenol

(from defensive secretion of(from defensive secretion of

a species of grasshopper)a species of grasshopper)

Example: 2,5-DichlorophenolExample: 2,5-DichlorophenolExample: 2,5-DichlorophenolExample: 2,5-Dichlorophenol

Dr. Wolf's CHM 201 & 202 22 - 33

Reactions of Phenols:Reactions of Phenols:

Electrophilic Aromatic Electrophilic Aromatic

SubstitutionSubstitution

Reactions of Phenols:Reactions of Phenols:

Electrophilic Aromatic Electrophilic Aromatic

SubstitutionSubstitution

Hydroxyl group strongly activates the ringHydroxyl group strongly activates the ringtoward electrophilic aromatic substitutiontoward electrophilic aromatic substitution

Dr. Wolf's CHM 201 & 202 22 - 34

HalogenationHalogenation

NitrationNitration

NitrosationNitrosation

SulfonationSulfonation

Friedel-Crafts AlkylationFriedel-Crafts Alkylation

Friedel-Crafts AcylationFriedel-Crafts Acylation

Electrophilic Aromatic Substitution in PhenolsElectrophilic Aromatic Substitution in PhenolsElectrophilic Aromatic Substitution in PhenolsElectrophilic Aromatic Substitution in Phenols

Dr. Wolf's CHM 201 & 202 22 - 35

HalogenationHalogenationHalogenationHalogenation

monohalogenation in nonpolar solventmonohalogenation in nonpolar solvent(1,2-dichloroethane)(1,2-dichloroethane)

++ BrBr22

ClCHClCH22CHCH22ClCl

0°C0°C

OOHH OOHH BrBr

(93%)(93%)

Dr. Wolf's CHM 201 & 202 22 - 36

HalogenationHalogenationHalogenationHalogenation

multiple halogenation in polar solventmultiple halogenation in polar solvent(water)(water)

++ 3Br3Br22

HH22OO

25°C25°C

OOHH FF

OOHH

BrBr

BrBrBrBr

FF

(95%)(95%)

Dr. Wolf's CHM 201 & 202 22 - 37


NitrationNitration






Dr. Wolf's CHM 201 & 202 22 - 38

NitrationNitrationNitrationNitration

HNOHNO33

acetic acidacetic acid5°C5°C

(73-77%)(73-77%)OH group controls OH group controls regiochemistryregiochemistry

OOHH CHCH33

OOHH

CHCH33

NNOO22

Dr. Wolf's CHM 201 & 202 22 - 39


NitrationNitration






Dr. Wolf's CHM 201 & 202 22 - 40

NitrosationNitrosationNitrosationNitrosation

NaNONaNO22

HH22SOSO44, H, H22OO

0°C0°C

OOHH

NNOO

(99%)(99%)only strongly activated only strongly activated rings undergo nitrosation rings undergo nitrosation when treated with nitrous when treated with nitrous acidacid

OOHH

Dr. Wolf's CHM 201 & 202 22 - 41


NitrationNitration






Dr. Wolf's CHM 201 & 202 22 - 42

OOHH

CHCH33HH33CC

SOSO33HH

(69%)(69%)

HH22SOSO44

100°C100°C

SulfonationSulfonationSulfonationSulfonation

OOHH

CHCH33HH33CC

OH group controls OH group controls regiochemistryregiochemistry

Dr. Wolf's CHM 201 & 202 22 - 43


NitrationNitration






Dr. Wolf's CHM 201 & 202 22 - 44

Friedel-Crafts AlkylationFriedel-Crafts AlkylationFriedel-Crafts AlkylationFriedel-Crafts Alkylation

(63%)(63%)

(CH(CH33))33COH reacts COH reacts

with Hwith H33POPO44 to give to give

(CH(CH33))33CC++

OOHH

CC

CHCH33

CHCH33HH33CC

CHCH33

HH33POPO44

60°C60°C

(CH(CH33))33COHCOH

OOHH

CHCH33

Dr. Wolf's CHM 201 & 202 22 - 45


NitrationNitration






Dr. Wolf's CHM 201 & 202 22 - 46

Acylation of PhenolsAcylation of PhenolsAcylation of PhenolsAcylation of Phenols

Acylation can take place either on the ringAcylation can take place either on the ringby electrophilic aromatic substitution or onby electrophilic aromatic substitution or onoxygen by nucleophilic acyl substitutionoxygen by nucleophilic acyl substitution

Dr. Wolf's CHM 201 & 202 22 - 47

Friedel-Crafts AcylationFriedel-Crafts AcylationFriedel-Crafts AcylationFriedel-Crafts Acylation

AlClAlCl33

OOHH

(74%)(74%)

CHCH33CClCCl

OO OOHH CC

OO CHCH33

++ ortho isomerortho isomer

(16%)(16%)

under Friedel-Crafts under Friedel-Crafts conditions, acylation conditions, acylation of the ring occursof the ring occurs(C-acylation)(C-acylation)

Dr. Wolf's CHM 201 & 202 22 - 48

O-AcylationO-AcylationO-AcylationO-Acylation

(95%)(95%)

in the absence of AlClin the absence of AlCl33, acylation of the , acylation of the

hydroxyl group occurs (O-acylation)hydroxyl group occurs (O-acylation)

OOHH

CHCH33(CH(CH22))66CClCCl

OO

++

OOC(CHC(CH22))66CHCH33 OO

Dr. Wolf's CHM 201 & 202 22 - 49

O- versus C-AcylationO- versus C-AcylationO- versus C-AcylationO- versus C-Acylation

OOC(CHC(CH22))66CHCH33 OO

OOHH CC

OO (CH(CH22))66CHCH33

AlClAlCl33

formed fasterformed faster more stablemore stableO-Acylation is kinetically controlled process; C-acylation is thermodynamically controlled

AlCl3 catalyzes the conversion of the aryl ester to the aryl alkyl ketones; this is called the Fries rearrangement

Dr. Wolf's CHM 201 & 202 22 - 50

Carboxylation of PhenolsCarboxylation of PhenolsCarboxylation of PhenolsCarboxylation of Phenols

Aspirin and Aspirin and the the

Kolbe-Schmitt Kolbe-Schmitt ReactionReaction COHCOH

OO

OCCHOCCH33

OO

Dr. Wolf's CHM 201 & 202 22 - 51

how is salicylic acid prepared?how is salicylic acid prepared?

Aspirin is prepared from salicylic acidAspirin is prepared from salicylic acidAspirin is prepared from salicylic acidAspirin is prepared from salicylic acid

COHCOH

OO

OOCCHCCH33

OO HH22SOSO44

COHCOH

OO

OOHHOO

CHCH33COCCHCOCCH33

OO

Dr. Wolf's CHM 201 & 202 22 - 52

called the Kolbe-Schmitt reactioncalled the Kolbe-Schmitt reaction

acidification converts the sodium salt shownacidification converts the sodium salt shownabove to salicylic acidabove to salicylic acid

Preparation of Salicylic AcidPreparation of Salicylic AcidPreparation of Salicylic AcidPreparation of Salicylic Acid

COCO22

125°C, 100 atm125°C, 100 atm

CONaCONa

OO

OHOHONaONa

Dr. Wolf's CHM 201 & 202 22 - 53

acid-base considerations provide an explanation:acid-base considerations provide an explanation:stronger base on left; weaker base on rightstronger base on left; weaker base on right

What Drives the Reaction?What Drives the Reaction?What Drives the Reaction?What Drives the Reaction?

++ COCO22

OO ––

••••••••••••

stronger base:stronger base:ppKKaa of conjugate of conjugate acid = 10acid = 10

weaker base:weaker base:ppKKaa of conjugate of conjugate acid = 3acid = 3

OO

––

••••••••••••CC

OO

OO

••••

••••HH

•••• ••••

Dr. Wolf's CHM 201 & 202 22 - 54

how does carbon-carbon bond form?how does carbon-carbon bond form?

recall electron delocalization in phenoxide ionrecall electron delocalization in phenoxide ion

negative charge shared by oxygen and by thenegative charge shared by oxygen and by thering carbons that are ortho and para to oxygenring carbons that are ortho and para to oxygen

Preparation of Salicylic AcidPreparation of Salicylic AcidPreparation of Salicylic AcidPreparation of Salicylic Acid

COCO22

125°C, 100 atm125°C, 100 atm

CONaCONa

OO

OHOHONaONa

Dr. Wolf's CHM 201 & 202 22 - 55

••••OO••••

HH

HH

HH

HH

HH

••••–– ••••OO

••••

HH

HH

HH

HH

HH

––•••• ••••OO

••••

HH

HH

HH

HH

HH––••••

••••OO••••

HH

HH

HH

HH

HH

––••••

Dr. Wolf's CHM 201 & 202 22 - 56

OO

CC

Mechanism of ortho CarboxylationMechanism of ortho CarboxylationMechanism of ortho CarboxylationMechanism of ortho Carboxylation

••••

••••

••••

•••• OO OO

HH

••••••••••••––

OO•••• ••••

HH

––

••••••••••••

CCOO

OO•••• ••••

Dr. Wolf's CHM 201 & 202 22 - 57

OO

CC

Mechanism of ortho CarboxylationMechanism of ortho CarboxylationMechanism of ortho CarboxylationMechanism of ortho Carboxylation

••••

••••OO

••••

•••• OO

HH

••••••••••••

––

OO•••• ••••

HH

––

••••••••••••

CCOO

OO•••• •••• OO

––

••••••••••••CC

OO

OO

••••

••••HH

•••• ••••

Dr. Wolf's CHM 201 & 202 22 - 58

Why ortho?Why ortho?

Why not para? Why not para?


Why not para? Why not para? OO••••••••••••

–– OO

––

••••••••••••CC

OO

OO

••••

••••HH

•••• ••••

OO••••

••••HH

CC

•••• ••••OO

OO••••••••••••––

Dr. Wolf's CHM 201 & 202 22 - 59

weaker base:pKa of conjugate acid = 3


Why not para? Why not para?


Why not para? Why not para? OO••••••••••••

–– OO

––

••••••••••••CC

OO

OO

••••

••••HH

•••• ••••

stronger base:pKa of conjugate acid = 4.5

OO••••

••••HH

CC

•••• ••••OO

OO••••••••••••––

Dr. Wolf's CHM 201 & 202 22 - 60

Hydrogen bonding between carboxylate and hydroxylHydrogen bonding between carboxylate and hydroxylgroup stabilizes salicylate ion. Salicylate is less basic group stabilizes salicylate ion. Salicylate is less basic than para isomer and predominates under conditionsthan para isomer and predominates under conditionsof thermodynamic control.of thermodynamic control.

Intramolecular Hydrogen BondingIntramolecular Hydrogen Bonding

in Salicylate Ionin Salicylate Ion

Intramolecular Hydrogen BondingIntramolecular Hydrogen Bonding

in Salicylate Ionin Salicylate Ion

OO

OO

CC OO ––

HH

Dr. Wolf's CHM 201 & 202 22 - 61

Preparation of Aryl EthersPreparation of Aryl EthersPreparation of Aryl EthersPreparation of Aryl Ethers

Dr. Wolf's CHM 201 & 202 22 - 62

Typical Preparation is by Williamson SynthesisTypical Preparation is by Williamson SynthesisTypical Preparation is by Williamson SynthesisTypical Preparation is by Williamson Synthesis OONaNa ++ RRXX

OORR NaNaXX++

SSNN22

Dr. Wolf's CHM 201 & 202 22 - 63

Typical Preparation is by Williamson SynthesisTypical Preparation is by Williamson SynthesisTypical Preparation is by Williamson SynthesisTypical Preparation is by Williamson Synthesis OONaNa ++ RRXX

OORR NaNaXX++

SSNN22

but the other combinationbut the other combination XX ++ RROONaNa

fails because aryl halides are normally unreactivefails because aryl halides are normally unreactivetoward nucleophilic substitutiontoward nucleophilic substitution

Dr. Wolf's CHM 201 & 202 22 - 64

acetoneacetone

heatheat

ExampleExampleExampleExample OONaNa ++ CHCH33II

OOCHCH33

(95%)(95%)

Dr. Wolf's CHM 201 & 202 22 - 65

acetone, heatacetone, heat

ExampleExampleExampleExample OOHH ++

(86%)(86%)

HH22CC CHCHCHCH22BrBr

KK22COCO33 OOCHCH22CHCH CHCH22

Dr. Wolf's CHM 201 & 202 22 - 66

Aryl Ethers from Aryl HalidesAryl Ethers from Aryl HalidesAryl Ethers from Aryl HalidesAryl Ethers from Aryl Halides FFNONO22

++ KKOOCHCH33

CHCH33OHOH

25°C25°C

OOCHCH33

NONO22

++ KKFF

(93%)(93%)

nucleophilic aromatic substitution is effective nucleophilic aromatic substitution is effective with nitro-substituted (ortho and/or para) aryl with nitro-substituted (ortho and/or para) aryl halides halides

Dr. Wolf's CHM 201 & 202 22 - 67

Cleavage of Aryl EthersCleavage of Aryl Ethersby Hydrogen Halidesby Hydrogen Halides

Cleavage of Aryl EthersCleavage of Aryl Ethersby Hydrogen Halidesby Hydrogen Halides

Dr. Wolf's CHM 201 & 202 22 - 68

Cleavage of Cleavage of AlkylAlkyl ArylAryl Ethers EthersCleavage of Cleavage of AlkylAlkyl ArylAryl Ethers Ethers

OO

ArAr

RR

HH++ ••••OO

ArAr

RR

•••••••• HH BrBr

••••••••

••••

••••••••

••••BrBr••••

––++ ++

Dr. Wolf's CHM 201 & 202 22 - 69

Cleavage of Cleavage of AlkylAlkyl ArylAryl Ethers EthersCleavage of Cleavage of AlkylAlkyl ArylAryl Ethers Ethers

OO

ArAr

RR

HH++ ••••OO

ArAr

RR

•••••••• HH BrBr

••••••••

••••

••••••••

••••BrBr••••

––++ ++

RR BrBr••••

••••••••

++ OO

ArAr••••

HH••••

An An alkylalkyl halide is halide is formed; never an formed; never an arylaryl halide! halide!

Dr. Wolf's CHM 201 & 202 22 - 70

++

ExampleExampleExampleExample OOCHCH33

OHOH

OHOH

OHOH

(85-87%)(85-87%)

CHCH33BrBr

(57-72%)(57-72%)

HBrHBr

heatheat

Dr. Wolf's CHM 201 & 202 22 - 71

Claisen RearrangementClaisen Rearrangement

of Allyl Aryl Ethersof Allyl Aryl Ethers

Claisen RearrangementClaisen Rearrangement

of Allyl Aryl Ethersof Allyl Aryl Ethers

Dr. Wolf's CHM 201 & 202 22 - 72

Allyl Aryl Ethers Rearrange on HeatingAllyl Aryl Ethers Rearrange on HeatingAllyl Aryl Ethers Rearrange on HeatingAllyl Aryl Ethers Rearrange on Heating

OHOH

CHCH22CHCH CHCH22

OCHOCH22CHCH CHCH22

200°C200°C

(73%)(73%)

allyl group allyl group migrates to migrates to ortho positionortho position

Dr. Wolf's CHM 201 & 202 22 - 73

rewrite as rewrite as

MechanismMechanismMechanismMechanism OCHOCH22CHCH CHCH22

OO OO

HH

keto-to-enolketo-to-enol

isomerizationisomerization

OHOH

Dr. Wolf's CHM 201 & 202 22 - 74

Claisen rearrangement is an example of a Claisen rearrangement is an example of a sigmatropic rearrangement. A sigmatropic rearrangement. A bond migrates bond migratesfrom one end of a conjugated from one end of a conjugated electron system electron systemto the other.to the other.

this this bond breaks bond breaks

this this bond forms bond forms

““conjugated conjugated electron system” electron system” is the allyl groupis the allyl group

Sigmatropic RearrangementSigmatropic RearrangementSigmatropic RearrangementSigmatropic Rearrangement OO

OO

HH

Dr. Wolf's CHM 201 & 202 22 - 75

Oxidation of Phenols:Oxidation of Phenols:QuinonesQuinones

Oxidation of Phenols:Oxidation of Phenols:QuinonesQuinones

Dr. Wolf's CHM 201 & 202 22 - 76

The most common examples of phenol oxidationsThe most common examples of phenol oxidationsare the oxidations of 1,2- and 1,4-benzenediolsare the oxidations of 1,2- and 1,4-benzenediolsto give quinones. to give quinones.

(76-81%)(76-81%)

QuinonesQuinonesQuinonesQuinones OHOH

OHOH

OO

OO

NaNa22CrCr22OO7,7, H H22SOSO44

HH22OO

Dr. Wolf's CHM 201 & 202 22 - 77

The most common examples of phenol oxidationsThe most common examples of phenol oxidationsare the oxidations of 1,2- and 1,4-benzenediolsare the oxidations of 1,2- and 1,4-benzenediolsto give quinones. to give quinones.

(68%)(68%)

QuinonesQuinonesQuinonesQuinones

OO

OOAgAg22OO

diethyl etherdiethyl ether

OHOH

OHOH

CHCH33

CHCH33

Dr. Wolf's CHM 201 & 202 22 - 78

AlizarinAlizarin(red pigment)(red pigment)

Some quinones are dyesSome quinones are dyesSome quinones are dyesSome quinones are dyes OO

OO

OHOH

OHOH

Dr. Wolf's CHM 201 & 202 22 - 79

Ubiquinone (Coenzyme Q)Ubiquinone (Coenzyme Q)nn = 6-10 = 6-10

involved in biological electron transportinvolved in biological electron transport

Some quinones are important biomoleculesSome quinones are important biomoleculesSome quinones are important biomoleculesSome quinones are important biomolecules

CHCH33OO

CHCH33OO

OO

OO

CHCH33

nn

Dr. Wolf's CHM 201 & 202 22 - 80

Vitamin KVitamin K(blood-clotting factor)(blood-clotting factor)

Some quinones are important biomoleculesSome quinones are important biomoleculesSome quinones are important biomoleculesSome quinones are important biomolecules OO

CHCH33

OO CHCH33 CHCH33 CHCH33 CHCH33

CHCH33

Dr. Wolf's CHM 201 & 202 22 - 81

Spectroscopic Analysis of PhenolsSpectroscopic Analysis of Phenols

Dr. Wolf's CHM 201 & 202 22 - 82

infrared spectra of phenols combine features infrared spectra of phenols combine features of alcohols and aromatic compoundsof alcohols and aromatic compounds

O—H stretch analogous to alcohols nearO—H stretch analogous to alcohols near3600 cm3600 cm-1-1

C—O stretch at 1200-1250 cmC—O stretch at 1200-1250 cm-1-1

Infrared SpectroscopyInfrared SpectroscopyInfrared SpectroscopyInfrared Spectroscopy

Dr. Wolf's CHM 201 & 202 22 - 83

2000200035003500 30003000 25002500 1000100015001500 500500

Wave number, cmWave number, cm-1-1

Figure 24.3: Infrared Spectrum of p-CresolFigure 24.3: Infrared Spectrum of p-Cresol

O—HO—H

C—HC—H

C—OC—O

CHCH33

OHOH

Dr. Wolf's CHM 201 & 202 22 - 84

Hydroxyl proton of OH group lies between alcoholsHydroxyl proton of OH group lies between alcoholsand carboxylic acids; range is and carboxylic acids; range is ca. ca. 4-12 ppm 4-12 ppm(depends on concentration). For (depends on concentration). For pp-cresol the OH-cresol the OHproton appears at proton appears at 5.1 ppm (Figure 24.4). 5.1 ppm (Figure 24.4).

1H NMR1H NMR CHCH33HOHO

HH HH

HHHH

Dr. Wolf's CHM 201 & 202 22 - 85

01.02.03.04.05.06.07.08.09.010.0

Chemical shift (Chemical shift (, ppm), ppm)

CCHH33HHOO

HH HH

HHHH

Dr. Wolf's CHM 201 & 202 22 - 86

CHCH33

OHOH

139.8139.8

21.321.3129.4129.4

112..3112..3 116.1116.1

155.1155.1

121.7121.7

Oxygen of hydroxyl group deshields carbonOxygen of hydroxyl group deshields carbonto which it is directly attached.to which it is directly attached.

The most shielded carbons of the ring are those thatThe most shielded carbons of the ring are those thatare ortho and para to the oxygen.are ortho and para to the oxygen.

13C NMR13C NMR

Dr. Wolf's CHM 201 & 202 22 - 87

maxmax

204 nm204 nm

256 nm256 nm

maxmax

210 nm210 nm

270 nm270 nm

maxmax

235 nm235 nm

287 nm287 nm

Oxygen substitution on ring shifts Oxygen substitution on ring shifts maxmax to longer to longer

wavelength; effect is greater in phenoxide ion.wavelength; effect is greater in phenoxide ion.

UV-VISUV-VIS OHOH

OO––

Dr. Wolf's CHM 201 & 202 22 - 88

Prominent peak for molecular ion. Most intense Prominent peak for molecular ion. Most intense peak in phenol is for molecular ion.peak in phenol is for molecular ion.

m/z m/z 9494

Mass SpectrometryMass Spectrometry OHOH••++

••••

Dr. Wolf's CHM 201 & 202 22 - 89

End of Chapter 22

dr. wolf's chm 201 & 20222 - 1 chapter 22 phenols

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delocalized negative

phenoxide iondr

phenoxide ion ohhhhhdr

hydrogen bonding

basis of phenol

effect of electron

phenol molecules

phenolsmany phenols