dr. wolf's chm 201 & 202 18-1 chapter 18 carboxylic acids

Dr. Wolf's CHM 201 & 202 18-1

Chapter 18Chapter 18Carboxylic AcidsCarboxylic Acids

Dr. Wolf's CHM 201 & 202 18-2

Carboxylic Acid NomenclatureCarboxylic Acid Nomenclature

Dr. Wolf's CHM 201 & 202 18-3

Table 18.1 Table 18.1 Table 18.1 Table 18.1

Systematic NameSystematic NameOO

HCOHHCOH methanoic acidmethanoic acid

OO

CHCH33COHCOH ethanoic acidethanoic acidOO

CHCH33(CH(CH22))1616COHCOH octadecanoic acidoctadecanoic acid

systematic IUPAC names replace "-e" systematic IUPAC names replace "-e" ending of alkane with "oic acid"ending of alkane with "oic acid"

Dr. Wolf's CHM 201 & 202 18-4

Table 18.1Table 18.1Table 18.1Table 18.1

Systematic NameSystematic Name Common NameCommon NameOO

HCOHHCOH methanoic acidmethanoic acid formic acidformic acid

OO

CHCH33COHCOH ethanoic acidethanoic acid acetic acidacetic acidOO

CHCH33(CH(CH22))1616COHCOH octadecanoic acidoctadecanoic acid stearic acidstearic acid

common names are based on natural origin common names are based on natural origin rather than structurerather than structure

Dr. Wolf's CHM 201 & 202 18-5

Table 18.1Table 18.1Table 18.1Table 18.1

Systematic NameSystematic Name Common NameCommon Name

2-hydroxypropanoic2-hydroxypropanoicacidacid

lactic acidlactic acid

((ZZ)-9-octadecenoic)-9-octadecenoicacidacid

oleic acidoleic acid

OO

CHCH33CHCOHCHCOH

OHOH OO

(CH(CH22))77COHCOH

CC CC

HH HH

CHCH33(CH(CH22))77

Dr. Wolf's CHM 201 & 202 18-6

Structure and BondingStructure and Bonding

Dr. Wolf's CHM 201 & 202 18-7

Formic acid is planarFormic acid is planarFormic acid is planarFormic acid is planar

Dr. Wolf's CHM 201 & 202 18-8

Formic acid is planarFormic acid is planarFormic acid is planarFormic acid is planar

CC OO

HH

HH

OO

120 pm120 pm

134 pm134 pm

Dr. Wolf's CHM 201 & 202 18-9

Electron DelocalizationElectron DelocalizationElectron DelocalizationElectron Delocalization

RRCC

OOHH

OO••••

•••• ••••

•••• RRCC

OOHH

OO••••

•••• ••••

••••++••••

––

Dr. Wolf's CHM 201 & 202 18-10

Electron DelocalizationElectron DelocalizationElectron DelocalizationElectron Delocalization

stabilizes carbonyl groupstabilizes carbonyl group

RRCC

OOHH

OO••••

•••• ••••

•••• RRCC

OOHH

OO••••

•••• ••••

••••++••••

–– RRCC

OOHH

OO••••

••••

••••

++

••••

––

Dr. Wolf's CHM 201 & 202 18-11

Physical PropertiesPhysical Properties

Dr. Wolf's CHM 201 & 202 18-12

Boiling PointsBoiling PointsBoiling PointsBoiling Points

Intermolecular forces, especially hydrogen Intermolecular forces, especially hydrogen bonding, are stronger in carboxylic acids than bonding, are stronger in carboxylic acids than in other compounds of similar shape and in other compounds of similar shape and molecular weightmolecular weight

bpbp 31°C31°C 80°C80°C 99°C99°C

OHOH

141°C141°C

OHOH

OO OO

Dr. Wolf's CHM 201 & 202 18-13

Hydrogen-bonded DimersHydrogen-bonded DimersHydrogen-bonded DimersHydrogen-bonded Dimers

Acetic acid exists as a hydrogen-bonded Acetic acid exists as a hydrogen-bonded dimer in the gas phase. The hydroxyl group dimer in the gas phase. The hydroxyl group of each molecule is hydrogen-bonded to the of each molecule is hydrogen-bonded to the carbonyl oxygen of the other.carbonyl oxygen of the other.

HH33CCCC

OO HH OO

CCHCCH33

OOHHOO

Dr. Wolf's CHM 201 & 202 18-14

Hydrogen-bonded DimersHydrogen-bonded DimersHydrogen-bonded DimersHydrogen-bonded Dimers

Acetic acid exists as a hydrogen-bonded Acetic acid exists as a hydrogen-bonded dimer in the gas phase. The hydroxyl group dimer in the gas phase. The hydroxyl group of each molecule is hydrogen-bonded to the of each molecule is hydrogen-bonded to the carbonyl oxygen of the other.carbonyl oxygen of the other.

Dr. Wolf's CHM 201 & 202 18-15

carboxylic acids are similar to alcohols in respect carboxylic acids are similar to alcohols in respect to their solubility in waterto their solubility in water

form hydrogen bonds to waterform hydrogen bonds to water

Solubility in WaterSolubility in WaterSolubility in WaterSolubility in Water

HH33CCCC

OO HH OO

OOHHOO

HH

HH

HH

Dr. Wolf's CHM 201 & 202 18-16

Acidity of Carboxylic AcidsAcidity of Carboxylic Acids

Most carboxylic acids have a pMost carboxylic acids have a pKKaa close to 5. close to 5.

Dr. Wolf's CHM 201 & 202 18-17

but carboxylic acids are far more acidic than alcoholsbut carboxylic acids are far more acidic than alcohols

Carboxylic acids are weak acidsCarboxylic acids are weak acidsCarboxylic acids are weak acidsCarboxylic acids are weak acids

CHCH33COCOHH

OO

CHCH33CHCH22OOHH

KKaa = 1.8 x 10 = 1.8 x 10-5-5

ppKKaa = 4.7 = 4.7KKaa = 10 = 10-16-16

ppKKaa = 16 = 16

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

GG°= 91 kJ/mol°= 91 kJ/mol



Free Energies of IonizationFree Energies of IonizationFree Energies of IonizationFree Energies of Ionization

CHCH33CHCH22OO– – + H+ H++

CHCH33CHCH22OHOH CHCH33COCOHH

OO

CHCH33COCO–– + H + H++

OO

Dr. Wolf's CHM 201 & 202 18-19

Greater acidity of carboxylic acids is attributedGreater acidity of carboxylic acids is attributedstabilization of carboxylate ion bystabilization of carboxylate ion by

Greater acidity of carboxylic acids is attributedGreater acidity of carboxylic acids is attributedstabilization of carboxylate ion bystabilization of carboxylate ion by

inductive effect of carbonyl groupinductive effect of carbonyl group

resonance stabilization of carboxylate ionresonance stabilization of carboxylate ion

RCRC

OO

OO++

––

RCRC

OO

OO

––••••

••••

••••

••••

•••• ••••

••••

RCRC

OO

OO––

••••

••••••••

Dr. Wolf's CHM 201 & 202 18-20

Figure 19.4: Electrostatic potential maps ofFigure 19.4: Electrostatic potential maps ofacetic acid and acetate ionacetic acid and acetate ion

Figure 19.4: Electrostatic potential maps ofFigure 19.4: Electrostatic potential maps ofacetic acid and acetate ionacetic acid and acetate ion

Acetic acidAcetic acid Acetate ionAcetate ion

Dr. Wolf's CHM 201 & 202 18-21

Substituents and Acid Strength

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

standard of comparison is acetic acid (standard of comparison is acetic acid (XX = H) = H)

Substituent Effects on AciditySubstituent Effects on Acidity

XX CHCH22COHCOH

OO

KKaa = 1.8 x 10 = 1.8 x 10-5-5

ppKKaa = 4.7 = 4.7

Dr. Wolf's CHM 201 & 202 18-23


alkyl substituents have negligible effectalkyl substituents have negligible effect

XX CHCH22COHCOH

OO

XX KKaa ppKKaa

HH

CHCH33

CHCH33(CH(CH22))55

1.8 x 101.8 x 10-5-5 4.74.7

1.3 x 101.3 x 10-5-5 4.94.9

1.3 x 101.3 x 10-5-5 4.94.9

Dr. Wolf's CHM 201 & 202 18-24


electronegative substituents increase acidityelectronegative substituents increase acidity

XX CHCH22COHCOH

OO

XX KKaa ppKKaa

HH

FF

ClCl

1.8 x 101.8 x 10-5-5 4.74.7

2.5 x 102.5 x 10-3-3 2.62.6

1.4 x 101.4 x 10-3-3 2.92.9

Dr. Wolf's CHM 201 & 202 18-25


electronegative substituents withdraw electronegative substituents withdraw electrons from carboxyl group; increase electrons from carboxyl group; increase KK for for loss of Hloss of H++

XX CHCH22COHCOH

OO

Dr. Wolf's CHM 201 & 202 18-26


effect of substituent decreases as number of bonds effect of substituent decreases as number of bonds between between XX and carboxyl group increases and carboxyl group increases

XX CHCH22COHCOH

OO

XX KKaa ppKKaa

HH 1.8 x 101.8 x 10-5-5 4.74.7

1.4 x 101.4 x 10-3-3 2.92.9

1.0 x 101.0 x 10-4-4 4.04.0ClCHClCH22

ClCl

3.0 x 103.0 x 10-5-5 4.54.5ClCHClCH22CHCH22

Dr. Wolf's CHM 201 & 202 18-27

Ionization ofSubstituted Benzoic Acids

Dr. Wolf's CHM 201 & 202 18-28

Hybridization EffectHybridization Effect

KKaa ppKKaa

6.3 x 106.3 x 10-5-5 4.24.2

5.5 x 105.5 x 10-5-5 4.34.3

1.4 x 101.4 x 10-2-2 1.81.8

COHCOH

OO

HH22CC CHCH COHCOH

OO

COHCOH

OO

HCHC CC

spsp22-hybridized carbon is more electron--hybridized carbon is more electron-withdrawing than withdrawing than spsp33, and , and spsp is more electron- is more electron-withdrawing than withdrawing than spsp22

Dr. Wolf's CHM 201 & 202 18-29

ppKKaa

SubstituentSubstituent orthoortho metameta paraparaHH 4.24.2 4.24.2 4.24.2CHCH33 3.93.9 4.34.3 4.44.4

FF 3.33.3 3.93.9 4.14.1ClCl 2.92.9 3.83.8 4.04.0CHCH33OO 4.14.1 4.14.1 4.54.5NONO22 2.22.2 3.53.5 3.43.4

Ionization of Substituted Benzoic AcidsIonization of Substituted Benzoic Acids COHCOH

OOXX effect is small unless X is effect is small unless X is

electronegative; effect is electronegative; effect is largest for ortho substituentlargest for ortho substituent

Dr. Wolf's CHM 201 & 202 18-30

Salts of Carboxylic Acids

Dr. Wolf's CHM 201 & 202 18-31

Carboxylic acids are neutralized by strong basesCarboxylic acids are neutralized by strong basesCarboxylic acids are neutralized by strong basesCarboxylic acids are neutralized by strong bases

equilibrium lies far to the right; equilibrium lies far to the right; KK is ~ 10 is ~ 101111

as long as the molecular weight of the acid is as long as the molecular weight of the acid is not too high, sodium and potassium not too high, sodium and potassium carboxylate salts are soluble in watercarboxylate salts are soluble in water

strongerstrongeracidacid

weakerweakeracidacid

RCOHRCOH ++ HOHO–– RCORCO–– ++ HH22OO

OOOO

Dr. Wolf's CHM 201 & 202 18-32

unbranched carboxylic acids with 12-18 carbonsunbranched carboxylic acids with 12-18 carbonsgive carboxylate salts that form give carboxylate salts that form micellesmicelles in inwaterwater

MicellesMicellesMicellesMicelles OO

ONaONasodium stearatesodium stearate

(sodium octadecanoate)(sodium octadecanoate)

CHCH33(CH(CH22))1616COCO

OO

NaNa++––

Dr. Wolf's CHM 201 & 202 18-33

MicellesMicellesMicellesMicelles OO

ONaONa

polarpolarnonpolarnonpolar

sodium stearate has a polar end (the carboxylate sodium stearate has a polar end (the carboxylate end) and a nonpolar "tail"end) and a nonpolar "tail"

the polar end is "water-loving" or hydrophilicthe polar end is "water-loving" or hydrophilic

the nonpolar tail is "water-hating" or hydrophobicthe nonpolar tail is "water-hating" or hydrophobic

in water, many stearate ions cluster together to form in water, many stearate ions cluster together to form spherical aggregates; carboxylate ions on the spherical aggregates; carboxylate ions on the outside and nonpolar tails on the insideoutside and nonpolar tails on the inside

Dr. Wolf's CHM 201 & 202 18-34

MicellesMicelles OO

ONaONa

polarpolarnonpolarnonpolar

Dr. Wolf's CHM 201 & 202 18-35

Figure 19.5 A micelleFigure 19.5 A micelleFigure 19.5 A micelleFigure 19.5 A micelle

Dr. Wolf's CHM 201 & 202 18-36

MicellesMicellesMicellesMicelles

The interior of the micelle is nonpolar and The interior of the micelle is nonpolar and has the capacity to dissolve nonpolar has the capacity to dissolve nonpolar substances.substances.

Soaps clean because they form micelles, Soaps clean because they form micelles, which are dispersed in water.which are dispersed in water.

Grease (not ordinarily soluble in water) Grease (not ordinarily soluble in water) dissolves in the interior of the micelle and is dissolves in the interior of the micelle and is washed away with the dispersed micelle.washed away with the dispersed micelle.

Dr. Wolf's CHM 201 & 202 18-37

Dicarboxylic Acids

Dr. Wolf's CHM 201 & 202 18-38

Dicarboxylic AcidsDicarboxylic Acids

one carboxyl group acts as an electron-one carboxyl group acts as an electron-withdrawing group toward the other; effect withdrawing group toward the other; effect decreases with increasing separationdecreases with increasing separation

Oxalic acidOxalic acid

Malonic acidMalonic acid

Heptanedioic acidHeptanedioic acid

1.21.2

2.82.8

4.34.3

COHCOH

OO

HOCHOC

OO ppKKaa

HOCCHHOCCH22COHCOH

OOOO

HOC(CHHOC(CH22))55COHCOH

OO OO

Dr. Wolf's CHM 201 & 202 18-39

Carbonic Acid

Dr. Wolf's CHM 201 & 202 18-40

Carbonic AcidCarbonic Acid

HOCOHHOCOH

OO

COCO22 ++ HH22OO

99.7%99.7% 0.3%0.3%

Dr. Wolf's CHM 201 & 202 18-41


HOCOHHOCOH

OO

COCO22 ++ HH22OO HOCOHOCO––

OO

HH++ ++

Dr. Wolf's CHM 201 & 202 18-42


HOCOHHOCOH

OO

COCO22 ++ HH22OO HOCOHOCO––

OO

HH++ ++

overall overall KK for these two steps = 4.3 x 10 for these two steps = 4.3 x 10-7-7

COCO22 is major species present in a solution of is major species present in a solution of

"carbonic acid" in acidic media"carbonic acid" in acidic media

Dr. Wolf's CHM 201 & 202 18-43


HOCOHOCO––

OO

––OCOOCO––

OO

HH++ ++

KKaa = 5.6 x 10 = 5.6 x 10-11-11Second ionization constant:Second ionization constant:

Dr. Wolf's CHM 201 & 202 18-44

Sources of Carboxylic Acids

Dr. Wolf's CHM 201 & 202 18-45

side-chain oxidation of alkylbenzenes (Chapter 11) side-chain oxidation of alkylbenzenes (Chapter 11)

oxidation of primary alcohols (Chapter 15)oxidation of primary alcohols (Chapter 15)

oxidation of aldehydes (Chapter 17)oxidation of aldehydes (Chapter 17)

Synthesis of Carboxylic Acids: Review

Synthesis of Carboxylic Acids: Review

Dr. Wolf's CHM 201 & 202 18-46

Synthesis of Carboxylic Acids by the Carboxylation of

Grignard Reagents

Dr. Wolf's CHM 201 & 202 18-47

Carboxylation of Grignard ReagentsCarboxylation of

Grignard Reagents

RXRXMgMg

diethyldiethyletherether

RMgXRMgXCCOO22

HH33OO++

RRCCOMgXOMgX

OO

RRCCOHOH

OOconverts an alkyl (or converts an alkyl (or aryl) halide to a aryl) halide to a carboxylic acid having carboxylic acid having one more carbon atom one more carbon atom than the starting halidethan the starting halide

Dr. Wolf's CHM 201 & 202 18-48

RR

MgXMgX

CC

OO

••••

•••• MgXMgX++

––

HH33OO++

diethyldiethyletherether

OO ••••••••

––

RR CC

OO••••

•••• ••••

OO ••••••••

RR CC

OHOH••••

••••

OO ••••••••

Carboxylation of Grignard ReagentsCarboxylation of

Grignard Reagents

Dr. Wolf's CHM 201 & 202 18-49

Example: Alkyl HalideExample: Alkyl Halide

CHCH33CHCHCHCH22CHCH33

(76-86%)(76-86%)

1. Mg,1. Mg, diethyl ether diethyl ether

2. 2. CCOO22

3. H3. H33OO++

CHCH33CHCHCHCH22CHCH33

ClCl CCOO22HH

Dr. Wolf's CHM 201 & 202 18-50

Example: Aryl HalideExample: Aryl Halide

(82%)(82%)

1. Mg,1. Mg, diethyl diethyl ether ether

2. 2. CCOO22

3. H3. H33OO++

CHCH33

CCOO22HHBrBr

CHCH33

Dr. Wolf's CHM 201 & 202 18-51

Synthesis of Carboxylic Acidsby the

Preparation and Hydrolysis of Nitriles

Dr. Wolf's CHM 201 & 202 18-52



RXRX RRCCOHOH

OO

converts an alkyl halide to a carboxylic acid having converts an alkyl halide to a carboxylic acid having one more carbon atom than the starting halideone more carbon atom than the starting halide

limitation is that the halide must be reactive toward limitation is that the halide must be reactive toward substitution by Ssubstitution by SNN2 mechanism, i.e. best with primary, 2 mechanism, i.e. best with primary, then secondary…… tertiary gives eliminationthen secondary…… tertiary gives elimination

–– ••••••••CC NNRRCC ••••NN

SSNN22

HH33OO++

heatheat + NH+ NH44++

Dr. Wolf's CHM 201 & 202 18-53

ExampleExample

NaNaCCNN

DMSODMSO

(77%)(77%)

HH22OO

HH22SOSO44

heatheat

(92%)(92%)

CHCH22ClCl

CHCH22CCNN

CHCH22CCOHOH

OO

Dr. Wolf's CHM 201 & 202 18-54

Example: Dicarboxylic AcidExample: Dicarboxylic Acid

BrBrCHCH22CHCH22CHCH22BrBr

NaNaCCNN HH22OO

HH22O, HClO, HCl heatheat

(77-86%)(77-86%)NNCCCHCH22CHCH22CHCH22CCNN

(83-85%)(83-85%)HOHOCCCHCH22CHCH22CHCH22CCOHOH

OOOO

Dr. Wolf's CHM 201 & 202 18-55

via Cyanohydrinvia Cyanohydrin

1. Na1. NaCCNN

2. H2. H++

(60% from 2-pentanone)(60% from 2-pentanone)

HH22OO

HCl, heatHCl, heat

CHCH33CCHCCH22CHCH22CHCH33

OO


OHOH

CCNN


OHOH

CCOO22HH

Dr. Wolf's CHM 201 & 202 18-56

Reactions of Carboxylic Acids:A Review and a Preview

Dr. Wolf's CHM 201 & 202 18-57

Reactions of Carboxylic AcidsReactions of Carboxylic AcidsReactions of Carboxylic AcidsReactions of Carboxylic Acids

Acidity (Chapter 18)Acidity (Chapter 18)

Reduction with LiAlHReduction with LiAlH4 4 (Chapter 15)(Chapter 15)

Esterification (Chapter 15)Esterification (Chapter 15)

Reaction with Thionyl Chloride (Chapter 12)Reaction with Thionyl Chloride (Chapter 12)

Reactions already discussedReactions already discussed

Dr. Wolf's CHM 201 & 202 18-58

Reactions of Carboxylic AcidsReactions of Carboxylic AcidsReactions of Carboxylic AcidsReactions of Carboxylic Acids

DecarboxylationDecarboxylation

But first we revisit acid-catalyzed esterificationBut first we revisit acid-catalyzed esterificationto examine its mechanism.to examine its mechanism.

New reaction in this chapterNew reaction in this chapter

Dr. Wolf's CHM 201 & 202 18-59

Mechanism of Acid-Catalyzed Esterification

Dr. Wolf's CHM 201 & 202 18-60

Acid-catalyzed EsterificationAcid-catalyzed Esterification

++ CHCH33OOHH

COHCOH

OOHH++

++ HH22OO

CCOOCHCH33

OO

Important fact: the Important fact: the oxygenoxygen of the alcohol is of the alcohol isincorporated into the ester as shown.incorporated into the ester as shown.

(also called Fischer esterification)(also called Fischer esterification)

Dr. Wolf's CHM 201 & 202 18-61

The mechanism involves two stages: The mechanism involves two stages:

1)1) formation of tetrahedral intermediateformation of tetrahedral intermediate(3 steps)(3 steps)

2)2) dissociation of tetrahedral intermediate dissociation of tetrahedral intermediate (3 steps)(3 steps)

Mechanism of Fischer Esterification


Dr. Wolf's CHM 201 & 202 18-62

The mechanism involves two stages: The mechanism involves two stages:

1)1) formation of tetrahedral intermediateformation of tetrahedral intermediate(3 steps)(3 steps)

2)2) dissociation of tetrahedral intermediate dissociation of tetrahedral intermediate (3 steps)(3 steps)



CC

OHOH

OHOH

OOCHCH33

tetrahedral intermediate in esterification tetrahedral intermediate in esterification of benzoic acid with methanolof benzoic acid with methanol

Dr. Wolf's CHM 201 & 202 18-63

First stage: formation of tetrahedral intermediate

First stage: formation of tetrahedral intermediate

CC

OHOH

OHOH

OOCHCH33

++ CHCH33OOHH

COHCOH

OO

HH++

methanol adds to the methanol adds to the carbonyl group of the carbonyl group of the carboxylic acidcarboxylic acid

the tetrahedral the tetrahedral intermediate is intermediate is analogous to a analogous to a hemiacetalhemiacetal

Dr. Wolf's CHM 201 & 202 18-64

Second stage: conversion of tetrahedral intermediate to esterSecond stage: conversion of

tetrahedral intermediate to ester

CC

OHOH

OHOH

OOCHCH33

++ HH22OO

HH++this stage corresponds this stage corresponds to an acid-catalyzed to an acid-catalyzed dehydrationdehydration

CCOOCHCH33

OO

Dr. Wolf's CHM 201 & 202 18-65

Mechanism of formationof

tetrahedral intermediate

Mechanism of formationof

tetrahedral intermediate

Dr. Wolf's CHM 201 & 202 18-66

Step 1Step 1 CC

OO

OO HH

•••• ••••

••••••••

OO ••••++HH

CHCH33

HH

Dr. Wolf's CHM 201 & 202 18-67

Step 1Step 1 CC

OO

OO HH

•••• ••••

••••••••

OO ••••++HH

CHCH33

HH

••••

CC

OO

OO HH

••••

••••

++ HH •••• OO ••••

CHCH33

HH

Dr. Wolf's CHM 201 & 202 18-68

Step 1Step 1

••••

CC

OO

OO HH

••••

••••

++ HH

carbonyl oxygen is carbonyl oxygen is protonated because protonated because cation produced is cation produced is stabilized by electron stabilized by electron delocalization delocalization (resonance)(resonance)

CC

OO

OO HH

••••••••

++

HH

••••

Dr. Wolf's CHM 201 & 202 18-69

Step 2Step 2

••••

CC

OO

OO HH

••••

••••

++ HH

•••• OO ••••

CHCH33

HH

Dr. Wolf's CHM 201 & 202 18-70

Step 2Step 2

••••

CC

OO

OO HH

••••

••••

++ HH

•••• OO ••••

CHCH33

HH

CC

OHOH

OHOH

••••••••

••••••••

OO ••••++

CHCH33

HH

Dr. Wolf's CHM 201 & 202 18-71

Step 3Step 3

•••• OO ••••

CHCH33

HH••••

CC

OHOH

OHOH

••••••••

••••

OO ••••

CHCH33

HH

++

Dr. Wolf's CHM 201 & 202 18-72

Step 3Step 3

•••• OO ••••

CHCH33

HH

••••

CC

OHOH

OHOH

••••••••

••••

OO ••••

CHCH33

HH

++ OO ••••

CHCH33

HH

HH++

••••

CC

OHOH

OHOH

••••••••

••••

OO ••••

CHCH33

••••

Dr. Wolf's CHM 201 & 202 18-73

Tetrahedral intermediateto

ester stage

Tetrahedral intermediateto

ester stage

Dr. Wolf's CHM 201 & 202 18-74

Step 4Step 4

••••

CC

OHOH

OO

••••••••

••••

OOCHCH33••••

••••

HH

Dr. Wolf's CHM 201 & 202 18-75

Step 4Step 4

OO ••••

CHCH33

HH

HH++••••

CC

OHOH

OO

••••••••

••••


••••

HH

Dr. Wolf's CHM 201 & 202 18-76

Step 4Step 4

OO ••••

CHCH33

HH

HH++••••

CC

OHOH

OO

••••••••

••••


••••

HH

••••

CC

OHOH

OO

••••••••


••••

HH HH++ •••• OO ••••

CHCH33

HH

Dr. Wolf's CHM 201 & 202 18-77

Step 5Step 5

••••

CC

OHOH

OO

••••••••


••••

HH HH++

Dr. Wolf's CHM 201 & 202 18-78

Step 5Step 5

••••

CC

OHOH

OO

••••••••


••••

HH HH++

OO••••HH HH••••

++

CC

OHOH••••••••


••••

++

Dr. Wolf's CHM 201 & 202 18-79

Step 5Step 5

CC

OHOH••••••••


••••

++

CC

OHOH••••


••••

++

Dr. Wolf's CHM 201 & 202 18-80

Step 6Step 6

CC

OO••••


••••

++ HH

OO••••

HH CHCH33•••• ++OOHH CHCH33••••

HH CC

OO••••


••••

••••

Dr. Wolf's CHM 201 & 202 18-81

Activation of carbonyl group by protonation of Activation of carbonyl group by protonation of carbonyl oxygencarbonyl oxygen

Nucleophilic addition of alcohol to carbonyl groupNucleophilic addition of alcohol to carbonyl groupforms tetrahedral intermediateforms tetrahedral intermediate

Elimination of water from tetrahedral intermediate Elimination of water from tetrahedral intermediate restores carbonyl grouprestores carbonyl group

Key Features of MechanismKey Features of Mechanism

Dr. Wolf's CHM 201 & 202 18-82

Intramolecular Ester Formation:Lactones

Dr. Wolf's CHM 201 & 202 18-83

Lactones are cyclic estersLactones are cyclic esters

Formed by intramolecular esterification in aFormed by intramolecular esterification in acompound that contains a hydroxyl group andcompound that contains a hydroxyl group anda carboxylic acid functiona carboxylic acid function

LactonesLactones

Dr. Wolf's CHM 201 & 202 18-84

ExamplesExamples

HHOOCHCH22CHCH22CHCH22COHCOH

OO OO

OO++ HH22OO

4-hydroxybutanoic acid4-hydroxybutanoic acid 4-butanolide4-butanolide

IUPAC nomenclature: replace the IUPAC nomenclature: replace the -oic acid -oic acid ending of the carboxylic acid by ending of the carboxylic acid by -olide-olide

identify the oxygenated carbon by numberidentify the oxygenated carbon by number

Dr. Wolf's CHM 201 & 202 18-85

ExamplesExamples

HHOOCHCH22CHCH22CHCH22COHCOH

OO

HHOOCHCH22CHCH22CHCH22CHCH22COHCOH

OO OO

OO

OO

OO++

++

HH22OO

HH22OO

4-hydroxybutanoic acid4-hydroxybutanoic acid

5-hydroxypentanoic acid5-hydroxypentanoic acid

4-butanolide4-butanolide

5-pentanolide5-pentanolide

Dr. Wolf's CHM 201 & 202 18-86

Common namesCommon names

OOOO

OO

OO

-butyrolactone-butyrolactone -valerolactone-valerolactone

Ring size is designated by Greek letter Ring size is designated by Greek letter corresponding to oxygenated carboncorresponding to oxygenated carbon

A A lactone has a five-membered ring lactone has a five-membered ring

A A lactone has a six-membered ring lactone has a six-membered ring

Dr. Wolf's CHM 201 & 202 18-87

Reactions designed to give hydroxy acids often Reactions designed to give hydroxy acids often yield the corresponding lactone, especially if theyield the corresponding lactone, especially if theresulting ring is 5- or 6-membered.resulting ring is 5- or 6-membered.

LactonesLactones

Dr. Wolf's CHM 201 & 202 18-88

ExampleExample

5-hexanolide (78%)5-hexanolide (78%)

OO

HH33CC

OO

CHCH33CCHCCH22CHCH22CHCH22COHCOH

OOOO

1. NaBH1. NaBH44

2. H2. H22O, HO, H++

Dr. Wolf's CHM 201 & 202 18-89

ExampleExample

5-hexanolide (78%)5-hexanolide (78%)

via:via: OO

HH33CC

OO

CHCH33CCHCCH22CHCH22CHCH22COHCOH

OOOO

1. NaBH1. NaBH44

2. H2. H22O, HO, H++

CHCH33CHCHCHCH22CHCH22CHCH22COHCOH

OOOOHH

Dr. Wolf's CHM 201 & 202 18-90

Decarboxylation of Malonic Acid

and Related Compounds

Dr. Wolf's CHM 201 & 202 18-91

Decarboxylation of Carboxylic Acids


Simple carboxylic acids do not decarboxylateSimple carboxylic acids do not decarboxylatereadily.readily.

RHRH ++ COCO22RCOHRCOH

OO

Dr. Wolf's CHM 201 & 202 18-92



Simple carboxylic acids do not decarboxylateSimple carboxylic acids do not decarboxylatereadily.readily.

But malonic acid does.But malonic acid does.

RHRH ++ COCO22RCOHRCOH

OO

150°C150°CCHCH33COHCOH

OO

++ COCO22HOCCHHOCCH22COHCOH

OO OO

Dr. Wolf's CHM 201 & 202 18-93

Mechanism of DecarboxylationMechanism of Decarboxylation

One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other. OO OO

OHOHHOHO

HH HH

OO

HOHO OO

OO

HH HH

HH

Dr. Wolf's CHM 201 & 202 18-94

Mechanism of DecarboxylationMechanism of Decarboxylation

This compound is This compound is the enol form of the enol form of acetic acid.acetic acid.

OO OO

OHOHHOHO

HH HH HH

HH

OHOH

HOHO

OO

HOHO OO

OO

HH HH

HH ++ CC

OO

OO

One carboxyl group assists the loss of the other.One carboxyl group assists the loss of the other.

Dr. Wolf's CHM 201 & 202 18-95

Mechanism of DecarboxylationMechanism of Decarboxylation OO OO

OHOHHOHO

HH HH HH

HH

OHOH

HOHO

OO

HOHO OO

OO

HH HH

HH ++ CC

OO

OO


HOCCHHOCCH33

OO

Dr. Wolf's CHM 201 & 202 18-96


OHOHHOHO

HH HH HH

HH

OHOH

HOHO

OO

HOHO OO

OO

HH HH

HH ++ CC

OO

OO


HOCCHHOCCH33

OO

These hydrogens play no role.These hydrogens play no role.

Dr. Wolf's CHM 201 & 202 18-97


OHOHHOHO

RR R'R' RR

R'R'

OHOH

HOHO

OO

HOHO OO

OO

RR R'R'

HH ++ CC

OO

OO


HOCCHHOCCHR'R'

OO

Groups other than H may be present.Groups other than H may be present.

RR

Dr. Wolf's CHM 201 & 202 18-98

185°C185°C

Decarboxylation is a general reaction for 1,3-dicarboxylic acids

Decarboxylation is a general reaction for 1,3-dicarboxylic acids

160°C160°C

COCO22HH

COCO22HH

COCO22HH

HH

(74%)(74%)

(96-99%)(96-99%)

CH(COCH(CO22H)H)22

CHCH22COCO22HH

Dr. Wolf's CHM 201 & 202 18-99


OHOHHOHO

RR R'R' RR

R'R'

OHOH

HOHO

OO

HOHO OO

OO

RR R'R'

HH ++ CC

OO

OO


This OH group plays no role.This OH group plays no role.

HOCCHHOCCHR'R'

OO

RR

Dr. Wolf's CHM 201 & 202 18-100


OHOHR"R"

RR R'R'

RR

CC

OO

OO


Groups other than OH may be present.Groups other than OH may be present.

R"R"CCHCCHR'R'

OO

RR

OO

OO

OO

RR R'R'

HH R"R"

R'R'

OHOH

++R"R"

Dr. Wolf's CHM 201 & 202 18-101


OHOHR"R"

RR R'R'

This kind of compoundThis kind of compoundis called a is called a -keto acid.-keto acid.

R"R"CCHCCHR'R'

OO

RR

Decarboxylation of a Decarboxylation of a -keto acid gives a -keto acid gives a ketone.ketone.

Dr. Wolf's CHM 201 & 202 18-102

Decarboxylation of a -Keto AcidDecarboxylation of a -Keto Acid

CCCHCH33CC

OO

CHCH33

CHCH33

COCO22HH25°C25°C

COCO22

CCCHCH33CC

OO

CHCH33

CHCH33

HH

++

Dr. Wolf's CHM 201 & 202 18-103

Spectroscopic Analysis ofSpectroscopic Analysis ofCarboxylic AcidsCarboxylic Acids

Dr. Wolf's CHM 201 & 202 18-104

A carboxylic acid is characterized by peaks due toA carboxylic acid is characterized by peaks due toOH and C=O groups in its infrared spectrum.OH and C=O groups in its infrared spectrum.

C=O stretching gives an intense absorptionC=O stretching gives an intense absorptionnear 1700 cmnear 1700 cm-1-1..

OH peak is broad and overlaps with C—H OH peak is broad and overlaps with C—H absorptions.absorptions.

Infrared SpectroscopyInfrared SpectroscopyInfrared SpectroscopyInfrared Spectroscopy

Dr. Wolf's CHM 201 & 202 18-105

2000200035003500 30003000 25002500 1000100015001500 500500

Wave number, cmWave number, cm-1-1

Figure 19.8 Infrared Spectrum of 4-Phenylbutanoic acidFigure 19.8 Infrared Spectrum of 4-Phenylbutanoic acidFigure 19.8 Infrared Spectrum of 4-Phenylbutanoic acidFigure 19.8 Infrared Spectrum of 4-Phenylbutanoic acid

C=OC=O

O—H and C—H stretchO—H and C—H stretch

monosubstitutedmonosubstitutedbenzenebenzene

CC66HH55CHCH22CHCH22CHCH22COCO22HH

Dr. Wolf's CHM 201 & 202 18-106

proton of OH group of a carboxylic acid is normallyproton of OH group of a carboxylic acid is normallythe least shielded of all of the protons in a the least shielded of all of the protons in a 11HHNMR spectrum: (NMR spectrum: ( 10-12 ppm; broad). 10-12 ppm; broad).

11H NMRH NMR11H NMRH NMR

Dr. Wolf's CHM 201 & 202 18-107

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

Figure 19.9Figure 19.9

CCHH22CCHH22CCHH22COCOHH

OO

01.02.03.04.05.06.07.08.09.010.011.012.0

Dr. Wolf's CHM 201 & 202 18-108

1313C NMRC NMR1313C NMRC NMR

Carbonyl carbon is at low field (Carbonyl carbon is at low field ( 160-185 ppm), 160-185 ppm), but not as deshielded as the carbonyl carbon of but not as deshielded as the carbonyl carbon of an aldehyde or ketone (an aldehyde or ketone ( 190-215 ppm). 190-215 ppm).

Dr. Wolf's CHM 201 & 202 18-109

UV-VISUV-VISUV-VISUV-VIS

Carboxylic acids absorb near 210 nm, butCarboxylic acids absorb near 210 nm, butUV-VIS spectroscopy has not proven to UV-VIS spectroscopy has not proven to be very useful for structure determination of be very useful for structure determination of carboxylic acids.carboxylic acids.

Dr. Wolf's CHM 201 & 202 18-110

Aliphatic carboxylic acids undergo a varietyAliphatic carboxylic acids undergo a varietyof fragmentations.of fragmentations.Aromatic carboxylic acids first form acylium ions,Aromatic carboxylic acids first form acylium ions,which then lose CO.which then lose CO.

Mass SpectrometryMass SpectrometryMass SpectrometryMass Spectrometry

ArCArCOHOH

••••OO ••

••

ArCArCOHOH

••++OO ••

••

ArCArC OO ••••

++ArAr+

+

Dr. Wolf's CHM 201 & 202 18-111

End of Chapter 18

dr. wolf's chm 201 & 202 18-1 chapter 18 carboxylic acids

Documents