14-1 Chemistry 2060, Spring 2060, LSU Chapter 14: Carboxylic Acids Sections 14.1-14.7.

14-1Chemistry 2060, Spring 2060, LSU

Chapter 14: Carboxylic AcidsChapter 14: Carboxylic Acids

Sections 14.1-14.7


SectionsSectionsChapter 14: Carboxylic AcidsChapter 14: Carboxylic Acids

1.1. IntroductionIntroduction2.2. Structure Structure 3.3. NomenclatureNomenclature4.4. Physical propertiesPhysical properties5.5. AcidityAcidity6.6. ReductionReduction7.7. Fisher esterificationFisher esterification8.8. Conversion to acid halidesConversion to acid halides9.9. DecaroxylationDecaroxylation


StructureStructureThe functional group of a carboxylic acid is a The functional group of a carboxylic acid is a

carboxyl groupcarboxyl group

• the general formula of an aliphatic carboxylic acid is RCOOH

• that of an aromatic carboxylic acid is ArCOOH

:

:

COOH CO2HCO H

O

::


NomenclatureNomenclatureIUPAC names: drop the IUPAC names: drop the -e-e from the parent alkane from the parent alkane

and add the suffix and add the suffix -oic acid-oic acid• if the compound contains a carbon-carbon double

bond, change the infix -anan- to -enen-

COOH C6H5COOH

3-Methylbutanoic acid(Isovaleric acid)

trans-3-Phenylpropenoic acid(Cinnamic acid)


NomenclatureNomenclatureThe carboxyl group takes precedence over most The carboxyl group takes precedence over most

other functional groupsother functional groups

5-Oxohexanoic acid 4-Aminobutanoic acid

(R)-5-Hydroxyhexanoic acid

COOH

OH

H2N COOHCOOHO


NomenclatureNomenclature• dicarboxylic acids: add -dioic aciddioic acid to the name of the

parent alkane containing both carboxyl groups• there is no need to use numbers to locate the carboxyl

groups; they can only be on the ends of the chain

HO OH

O

Propanedioic acid(Malonic acid)

Ethanedioic acid(Oxalic acid)

OHO

OH

O

O

Hexanedioic acid(Adipic acid)

Pentanedioic acid(Glutaric acid)

Butanedioic acid(Succinic acid)

OOH

OHO

OH

O

HO

OHO

OH

O

O


NomenclatureNomenclature• if the carboxyl group is bonded to a ring, name the ring

compound and add the suffix -carboxylic acidcarboxylic acid

3

21

2-Cyclohexene-carboxylic acid

trans-1,3-Cyclopentane-dicarboxylic acid

COOHCOOHHOOC


NomenclatureNomenclature• benzoic acid is the simplest aromatic carboxylic acid• use numbers to show the location of substituents

Benzoicacid

2-Hydroxybenzoic acid

(Salicylic acid)

COOH COOHOH

1,2-Benzene-dicarboxylic acid(Phthalic acid)

1,4-Benzene-dicarboxylic acid

(Terephthalic acid)

COOHCOOH

COOH

COOH


NomenclatureNomenclature• when common names are used, the letters

etc. are often used to locate substituents

• in common nomenclature, ketoketo indicates the presence of a ketone, and CH3CO- is named an aceto groupaceto group

alanine)(-Aminopropionic acid;(-Aminobutyric acid;

GABA)

2-Aminopropanoic acid4-Aminobutanoic acid

4 32

5 H2NOH

O

OH

O

NH2

OH

O

1

OH

OOO

CH3C-3-oxobutanoic acid-Ketobutyric acid;

acetoacetic acid)

Acetyl group(aceto group)


Physical PropertiesPhysical PropertiesIn the liquid and solid states, carboxylic acids are In the liquid and solid states, carboxylic acids are

associated by hydrogen bonding into dimeric associated by hydrogen bonding into dimeric structuresstructures


Physical PropertiesPhysical PropertiesCarboxylic acids have significantly higher boiling Carboxylic acids have significantly higher boiling

points than other types of organic compounds of points than other types of organic compounds of comparable molecular weightcomparable molecular weight• they are polar compounds and form very strong

intermolecular hydrogen bonds

Carboxylic acids are more soluble in water than Carboxylic acids are more soluble in water than alcohols, ethers, aldehydes, and ketones of alcohols, ethers, aldehydes, and ketones of comparable molecular weightcomparable molecular weight• they form hydrogen bonds with water molecules

through their C=O and OH groups


Physical PropertiesPhysical Properties• water solubility decreases as the relative size of the

hydrophobic portion of the molecule increases


AcidityAcidityCarboxylic acids are weak acidsCarboxylic acids are weak acids

• values of pKa for most aliphatic and aromatic carboxylic acids fall within the range 4 to 5

• the greater acidity of carboxylic acids relative to alcohols, both of which contain an OH group, is due to resonance stabilization of the carboxylate anion

CH3COOH H2O CH3COO- H3O+

[CH3COO-][H3O+][CH3COOH]

+

= 1.74 x 10-5Ka =

pKa = 4.76

+


AcidityAcidityelectron-withdrawing substituents near the electron-withdrawing substituents near the

carboxyl group increase acidity through their carboxyl group increase acidity through their inductive effectinductive effect

CH3COOH ClCH2COOH Cl2CHCOOH Cl3CCOOH

pKa:

Increasing acid strength

2.86

Chloroaceticacid

0.70

Trichloroacetic acid

1.48

Dichloroacetic acid

Aceticacid4.76


AcidityAcidity• the acid-strengthening effect of a halogen substituent

falls off rapidly with increasing distance from the carboxyl group

COOH

Cl

COOHCl

COOHCl COOH

2-Chlorobutanoicacid

(pKa 2.83)


(pKa 3.98)


(pKa 4.52)

Butanoicacid

(pKa 4.82)

Decreasing acid strength


Reaction with BasesReaction with BasesCarboxylic acids, whether soluble or insoluble in Carboxylic acids, whether soluble or insoluble in

water, react with NaOH, KOH, and other strong water, react with NaOH, KOH, and other strong bases to give water-soluble saltsbases to give water-soluble salts

They also form water-soluble salts with ammonia They also form water-soluble salts with ammonia and aminesand amines

+ +

Benzoic acid(slightly soluble

in water)

Sodium benzoate(60 g/100 mL water)

COOH COO-Na

+NaOH

H2 OH2 O

+

Ammonium benzoate(20 g/100 mL water)

Benzoic acid(slightly soluble

in water)

COOH COO-NH4

+NH3 H2 O


Reaction with BasesReaction with BasesCarboxylic acids react with sodium bicarbonate and Carboxylic acids react with sodium bicarbonate and

sodium carbonate to form water-soluble salts and sodium carbonate to form water-soluble salts and carbonic acidcarbonic acid• carbonic acid, in turn, breaks down to carbon dioxide

and water

CH3COOH Na+HCO3

- H2O

H2CO3

CH3COOH Na+HCO3

-

CO2

CH3COO-Na

+

CH3COO-Na

+

H2O

CO2

H2CO3

H2O

+ +

+

+ ++


Reaction with BasesReaction with Bases


ReductionReductionThe carboxyl group is very resistant to reductionThe carboxyl group is very resistant to reduction

• it is not affected by catalytic hydrogenation under conditions that easily reduce aldehydes and ketones to alcohols, and reduce alkenes and alkynes to alkanes

• it is not reduced by NaBH4


ReductionReductionLithium aluminum hydride reduces a carboxyl Lithium aluminum hydride reduces a carboxyl

group to a 1° alcoholgroup to a 1° alcohol• reduction is carried out in diethyl ether, THF, or other

nonreactive, aprotic solvents

1. LiAlH4, ether2. H2O

LiOH Al(OH)3+ +H

O

OH


Selective ReductionSelective ReductionCatalytic hydrogenation does not reduce a COOH Catalytic hydrogenation does not reduce a COOH

groupgroup• we can use H2/M to reduce an alkene in the presence of

a COOH group

• we can use NaBH4 to reduce an aldehyde or ketone in the presence of a COOH group

OH

O

H2+Pt

OH

O

Hexanoic acid5-Hexenoic acid25°C, 2 atm

C6H5 OH

OO1. NaBH4

2. H2OC6H5 OH

OOH

5-Hydroxy-5-phenylpentanoic acid5-Oxo-5-phenylpentanoic acid


Fischer EsterificationFischer EsterificationEsters can be prepared by treating a carboxylic Esters can be prepared by treating a carboxylic

acid with an alcohol in the presence of an acid acid with an alcohol in the presence of an acid catalyst, commonly Hcatalyst, commonly H22SOSO44 or gaseous HCl or gaseous HCl

CH3COHO

CH3CH2OHH2SO4

CH3COCH2CH3

OH2O

Ethanoic acid(Acetic acid)

++

Ethyl ethanoate(Ethyl acetate)

Ethanol(Ethyl alcohol)


Fischer EsterificationFischer EsterificationFischer esterification is an equilibrium reactionFischer esterification is an equilibrium reaction

• by careful control of experimental conditions, it is possible to prepare esters in high yield

• if the alcohol is inexpensive relative to the carboxylic acid, it can be used in excess to drive the equilibrium to the right

• a key intermediate in Fischer esterification is the tetrahedral carbonyl addition intermediate formed by addition of ROH to the C=O group

C OHRO

HOCH3

H+

C OCH3

OH

OR

H

H+

C OCH3RO

HOH+ +


Acid ChloridesAcid Chlorides

The functional group of an acid halide is a carbonyl The functional group of an acid halide is a carbonyl group bonded to a halogen atomgroup bonded to a halogen atom• among the acid halides, acid chlorides are by far the

most common and the most widely used

Functional group of an acid halide

Acetylchloride

Benzoylchloride

-C-X CH3CCl

O OC-Cl

O


Acid ChloridesAcid ChloridesAcid chlorides are most often prepared by treating Acid chlorides are most often prepared by treating

a carboxylic acid with thionyl chloridea carboxylic acid with thionyl chloride

+ + +

Butanoicacid

Thionylchloride

Butanoylchloride

SOCl2 SO2 HClOH

O

Cl

O


DecarboxylationDecarboxylationDecarboxylation:Decarboxylation: loss of COloss of CO22 from a carboxyl group from a carboxyl group

• most carboxylic acids, if heated to a very high temperature, undergo thermal decarboxylation

• most carboxylic acids, however, are quite resistant to

• moderate heat and melt or even boil without decarboxylation

RCOH

O

RH CO2decarboxylation +

heat


DecarboxylationDecarboxylation• exceptions are carboxylic acids that have a carbonyl

group beta to the carboxyl group• this type of carboxylic acid undergoes decarboxylation

on mild heating

OH

OO O

CO2Acetone3-Oxobutanoic acid

(Acetoacetic acid)

+warm


DecarboxylationDecarboxylation• thermal decarboxylation of a -ketoacid involves

rearrangement of six electrons in a cyclic six-membered transition state

O+

enol ofa ketone

(A cyclic six-membered transition state)

CO2(1) (2)

O OH

O

O

C

OH

O


DecarboxylationDecarboxylation• thermal decarboxylation of malonic acids also involves

rearrangement of six electrons in a cyclic six-membered transition state

O OH

HO O

OH

HOC

O

O HO

OCO2+

Enol of acarboxylic acid

A cyclic six-membered transition state

(1) (2)


DecarboxylationDecarboxylation• Problem:Problem: draw the product of decarboxylation

• Problem:Problem: draw the -ketoacid that undergoes decarboxylation to give this ketone

OCOOH heat

O

CO2-ketoacidheat +

14-1 Chemistry 2060, Spring 2060, LSU Chapter 14: Carboxylic Acids Sections 14.1-14.7.

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Transcript of 14-1 Chemistry 2060, Spring 2060, LSU Chapter 14: Carboxylic Acids Sections 14.1-14.7.