18 18-1 © 2003 thomson learning, inc. all rights reserved general, organic, and biochemistry, 7e...

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18-1© 2003 Thomson Learning, Inc.All rights reserved

General, Organic, and General, Organic, and Biochemistry, 7eBiochemistry, 7e

Bettelheim,Bettelheim,

Brown, and MarchBrown, and March

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Chapter 18Chapter 18

Carboxylic Acids, Carboxylic Acids, Anhydrides, Esters, Anhydrides, Esters, and Amidesand Amides

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IntroductionIntroduction• In this chapter, we study carboxylic acids,

another class of organic compounds containing the carbonyl group • we also study three classes of compounds derived

from carboxylic acids; anhydrides, esters, and amides

• each is related to a carboxyl group by loss of H2O

RCOHO

RCOR'O

RCOCR'O O

RCNH2

O

RC-OHO

H-OCR'O

RC-OHO

H-OR' RC-OHO

H-NH2

A carboxylic acid An esterAn anhydride An amide

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Carboxylic AcidsCarboxylic Acids• The functional group of a carboxylic acid is a

carboxyl groupcarboxyl group, which can be represented in any one of three ways

CO2HCOOHC-OHO

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NomenclatureNomenclature• IUPAC names

• for an acyclic carboxylic acid, take longest carbon chain that contains the carboxyl group as the parent alkane

• drop the final -ee from the name of the parent alkane and replace it by -oic acidoic acid

• number the chain beginning with the carbon of the carboxyl group

• because the carboxyl carbon is understood to be carbon 1, there is no need to give it a number

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NomenclatureNomenclature• in these examples, the common name is given in

parentheses

• an -OH substituent is indicated by the prefix hydroxy-; an -NH2 substituent by the prefix amino-

3-Methylbutanoic acid(Isovaleric acid)

Hexanoic acid(Caproic acid)

OH

O

OH

O1 1

63

OH

OOHH2N COOH

5-Hydroxyhexanoic acid

15

4-Aminobenzoic acid

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NomenclatureNomenclature• to name a dicarboxylic acid, add the suffix -dioic aciddioic acid

to the name of the parent alkane that contains both carboxyl groups

• the numbers of the carboxyl carbons are not indicated because they can be only at the ends of the chain

O

HOOH

O

Butanedioic acid(Succinic acid)

Ethanedioic acid(Oxalic acid)

Hexanedioic acid(Adipic acid)

Propanedioic acid(Malonic acid)

HO OH

O

OOH

O

OH

O

O

HO

O

HO

1 1

1 1

2 3

4 6OH

O

HO15

O

Pentanedioic acid(Glutaric acid)

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CH3COOHHCOOH

CH3CH2COOHCH3(CH2)2COOHCH3(CH2)3COOHCH3(CH2)4COOHCH3(CH2)6COOHCH3(CH2)8COOHCH3(CH2)10COOHCH3(CH2)12COOHCH3(CH2)14COOHCH3(CH2)16COOHCH3(CH2)18COOH

DerivationCommon Name

IUPAC Name(acid)Structure

Greek: arachis, peanutGreek: stear, solid fatLatin: palma, palm treeGreek: myristikos, fragrantLatin: laurus, laurelLatin: caper, goatLatin: caper, goatLatin: caper, goatLatin: valere, to be strongLatin: butyrum, butterGreek: propion, first fatLatin: acetum, vinegarLatin: formica, ant

arachidicstearicpalmiticmyristiclauric

capriccapryliccaproicvalericbutyricpropionicaceticformic

eicosanoicoctadecanoichexadecanoictetradecanoicdodecanoicdecanoicoctanoichexanoicpentanoicbutanoicpropanoicethanoicmethanoic

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NomenclatureNomenclature• for common names, use, the Greek letters alpha (),

beta (), gamma (), and so forth to locate substituents

C-C-C-C-OHO

OHH2N

O

OHOH

O

(-Aminobutyric acid; GABA)2-Hydroxypropanoic acid4-Aminobutanoic acid

4 3 2

1

4

1

2

(-Hydroxypropionic acid;lactic acid)

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Physical PropertiesPhysical Properties• The carboxyl group contains three polar covalent

bonds; C=O, C-O, and O-H• the polarity of these bonds determines the major

physical properties of carboxylic acids

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Physical PropertiesPhysical Properties• carboxylic acids have significantly higher boiling

points than other types of organic compounds of comparable molecular weight

• their higher boiling points are a result of their polarity and the fact that hydrogen bonding between two carboxyl groups creates a dimer that behaves as a higher-molecular-weight compound

H3C C

O

O

H

CH3C

O

O

H- +

+ -

hydrogen bondingbetween two molecules

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Physical PropertiesPhysical Properties• carboxylic acids are more soluble in water than are

alcohols, ethers, aldehydes, and ketones of comparable molecular weight

CH3COOHCH3CH2CH2OHCH3CH2CHO

CH3(CH2)2COOHCH3(CH2)3CH2OHCH3(CH2)3CHO

acetic acid

1-propanolpropanal

60.5

60.158.1

1189748

16388.1butanoic acid1-pentanol 88.1 137

103pentanal 86.1

Structure NameMolecularWeight

Boiling Point (°C)

Solubility(g/100 mL H2O)

infinite

infinite

16infinite

2.3slight

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Acidity of RCOOHAcidity of RCOOH• Carboxylic acids are weak acids

• values of Ka for most unsubstituted aliphatic and aromatic carboxylic acids fall within the range 10-4 to 10-5 (pKa 4.0 - 5.0)

CH3COHO

H2O CH3CO-

OH3O

+

[CH3COO-][H3O+]

[CH3COOH]= 1.74 x 10-5Ka =

pKa = 4.76

++

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Acidity of RCOOHAcidity of RCOOH• substituents of high electronegativity, especially -OH, -

Cl, and -NH3+, near the carboxyl group increase the

acidity of carboxylic acids• both dichloroacetic acid and trichloroacetic acid are

stronger acids than H3PO4 (pKa 2.1)

CH3COOH ClCH2COOH Cl2CHCOOH Cl3CCOOHFormula:

pKa:

Name:

Increasing acid strength2.86

Chloroaceticacid

0.70

Trichloroaceticacid

1.48

Dichloroacetic acid

Acetic acid4.76

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Reaction With BasesReaction With Bases• All carboxylic acids, whether soluble or insoluble

in water, react with NaOH, KOH, and other strong bases to form water-soluble salts

• they also form water-soluble salts with ammonia and amines

COOH NaOHH2O

COO- Na

+H2O+ +

Benzoic acid(slightly soluble in water)

Sodium benzoate(60 g/100 mL water)

COOH NH3H2O

COO- NH4

++

Ammonium benzoate(20 g/100 mL water)

Benzoic acid(slightly soluble in water)

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Reaction With BasesReaction With Bases• like inorganic acids, carboxylic acids react with sodium

bicarbonate and sodium carbonate to form water-soluble sodium salts and carbonic acid

• carbonic acid then decomposes to give water and carbon dioxide, which evolves as a gas

CH3COOH NaHCO3H2O

CH3COO- Na

+CO2 H2O+ + +

Acetic acid Sodium acetate

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Ionization versus pHIonization versus pH• The form in which a carboxylic acid exist in an

aqueous solution depends on the solution’s pH

R-C-OHO OH-

H+ R-C-OHO

R-C-O-O

H+

OH-

R-C-O-O

at pH 2.0or lower

at pH 8.0or higher

+

at pH = pKa = 4.0 - 5.0both forms are present in

approximately equal amounts

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AnhydridesAnhydrides• The functional group of an anhydrideanhydride is two

carbonyl groups bonded to the same oxygen• the anhydride may be symmetrical (from two identical

acyl groups), or mixed (from two different acyl groups)• to name an anhydride, drop the word "acidacid" from the

name of the carboxylic acid from which the anhydride is derived and add the word "anhydrideanhydride"

Acetic anhydrideCH3C-O-CCH3

O O

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EstersEsters• The functional group of an esterester is a carbonyl

group bonded to an -OR group• both IUPAC and common names of esters are derived

from the names of the parent carboxylic acids• name the alkyl or aryl group bonded to oxygen first,

followed by the name of the acid; replace the suffix -icic acidacid by -ateate

• a cyclic ester is called a lactonelactone

CH3COCH2CH3

OO O

OO

O

O

A five-memberedlactone

Ethyl ethanoate(Ethyl acetate)

Diethyl pentanedioate(Diethyl glutarate)

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AmidesAmides• The functional group of an amideamide is a carbonyl

group bonded to a nitrogen atom• to name an amide, drop the suffix -oic acidoic acid from the

IUPAC name of the parent acid, or -ic acidic acid from its common name, and add -amideamide

• if the amide nitrogen is bonded to an alkyl or aryl group, name the group and show its location on nitrogen by N- ; two alkyl or aryl groups by N,N-di-

CH3CNH2

OCH3CNHCH3

OHCN(CH3)2

O

N-Methylacetamide(a 2° amide)

Acetamide(a 1° amide)

N,N-Dimethylformamide(a 3° amide)

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AmidesAmides• a cyclic amide is called a lactamlactam

• the penicillins are referred to as -lactam antibiotics

O

NH

O

NH

A four-membered lactam(a -lactam)

A seven-membered lactam

N

CH3

NH2

OHO

NHO

S

CH3

COOH

The penicillinsdiffer in the groupbonded to thecarbonyl carbon

The-lactam ring

Amoxicillin

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AmidesAmides• the cephalosporins are also -lactam antibiotics

N

S

COOHO CH3

NHNH2

O

Cefalexin(a -lactam antibiotic)

The cephalosporinsdiffer in the groupbonded to the carbonylcarbon...

...and the group bonded to this carbon of the six-membered ring

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Fischer EsterificationFischer Esterification• Fischer esterificationFischer esterification is one of the most

commonly used preparations of esters• in Fischer esterification, a carboxylic acid is reacted

with an alcohol in the presence of an acid catalyst, such as concentrated sulfuric acid

• Fischer esterification is reversible• it is possible to drive it in either direction by the choice

of experimental conditions (Le Chatelier’s principle)

CH3C-OHO

H-OCH2CH3

H2SO4CH3COCH2CH3

OH2O

Ethanoic acid(Acetic acid)

++

Ethyl ethanoate(Ethyl acetate)

Ethanol(Ethyl alcohol)

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Fischer EsterificationFischer Esterification• in Fischer esterification, the alcohol adds to the

carbonyl group of the carboxylic acid to form a tetrahedral carbonyl addition intermediate

• the intermediate then loses H2O to give an ester

CH3CO

OH

OCH2CH3

H H2SO4CH3C

O-HOCH2CH3

OH

H2SO4CH3COCH2CH3

OH2O+

+

A tetrahedral carbonyladdition intermediate

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Preparation of AmidesPreparation of Amides• In principle, we can form an amide by treating a

carboxylic acid with an amine and removing -OH from the acid and an -H from the amine• in practice what occurs if the two are mixed is an acid-

base reaction to form an ammonium salt• if this salt is heated to a high enough temperature,

water is eliminated and an amide forms

H2OCH3C-NHCH2CH3

O

CH3C-O- H3NCH2CH3

OH2NCH2CH3CH3C-OH

O+

Aceticacid

Ethanamine(Ethylamine)

An ammonium salt

heat +

An amide

+

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Preparation of AmidesPreparation of Amides• it is much more common to prepare amides by treating

an amine with an anhydride

CH3C-O-CCH3

O OH2NCH2CH3 CH3C-NHCH2CH3

OCH3COH

O+ +

Acetic anhdyride An amide

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Hydrolysis of Anhydrides Hydrolysis of Anhydrides • carboxylic anhydrides, particularly the low-molecular-

weight ones, react readily with water to give two carboxylic acids

CH3COCCH3

O OH2O CH3COH

OHOCCH3

O+ +

Acetic anhydride Acetic acid Acetic acid

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Hydrolysis of EstersHydrolysis of Esters• esters hydrolyze only very slowly, even in boiling water• hydrolysis becomes considerably more rapid, however,

when the ester is heated in aqueous acid or base• hydrolysis of esters in aqueous acid is the reverse of

Fischer esterification• a large excess of water drives the equilibrium to the

right to form the carboxylic acid and alcohol (Le Chatelier's principle)

CH3COCH2CH3

O

H2OH+

CH3COHO

CH3CH2OH+ +

Ethyl acetate Acetic acid Ethanol

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Hydrolysis of EstersHydrolysis of Esters• we can also hydrolysis of an ester using a hot aqueous

base, such as aqueous NaOH• this reaction is often called saponificationsaponification, a reference

to its use in the manufacture of soaps• the carboxylic acid formed in the hydrolysis reacts with

hydroxide ion to form a carboxylic acid anion• each mole of ester hydrolyzed requires one mole of

base

CH3COCH2CH3

ONaOH

H2OCH3CO-Na+

OCH3CH2OH

Sodiumhydroxide

+ +

Ethyl acetate Sodiumacetate

Ethanol

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Hydrolysis of AmidesHydrolysis of Amides• amides require more vigorous conditions for

hydrolysis in both acid and base than do esters• hydrolysis in hot aqueous acid gives a carboxylic acid

and an ammonium ion• hydrolysis is driven to completion by the acid-base

reaction between ammonia or the amine and the acid to form an ammonium ion

• each mole of amide requires one mole of acid

CH3CH2CH2CNH2

OH2O HCl

H2OCH3CH2CH2COH

ONH4

+Cl

-

Butanoic acidButanamide

++ +heat

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Hydrolysis of AmidesHydrolysis of Amides• hydrolysis of an amide in aqueous base gives a

carboxylic acid salt and ammonia or an amine• hydrolysis is driven to completion by the acid-base

reaction between the carboxylic acid and base to form a salt

• each mole of amide requires one mole of base

CH3CNHO

NaOHH2O

CH3CO-Na+O

H2N

AnilineSodiumacetate

Acetanilide

++heat

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Phosphoric AnhydridesPhosphoric Anhydrides• the functional group of a phosphoric anhydridephosphoric anhydride is two

phosphoryl (P=O) groups bonded to the same oxygen atom

HO-P-O-P-OHOH OH

O O

O-

-O-P-O-P-O-O O

O-

OH OH

HO-P-O-P-O-P-OH

OH

O O O-O-P-O-P-O-P-O-

O O O

O- O- O-

Triphosphoric acid

Diphosphate ion(Pyrophosphate ion)

Diphosphoric acid(Pyrophosphoric acid)

Triphosphate ion

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Phosphoric EstersPhosphoric Esters• phosphoric acid forms mono-, di-, and triphosphoric

esters• in more complex phosphoric esters, it is common to

name the organic molecule and then indicate the presence of the phosphoric ester by either the word "phosphate" or the prefix phospho-

• dihydroxyacetone phosphate and pyridoxal phosphate are shown as they are ionized at pH 7.4, the pH of blood plasma

CH3O-P-OHOCH3

O CCH2-O-P-O-

O O

O-

CH2OH

N

HO

H3C

CH2O-P-O-CHO O

O-

Dimethyl phosphate Dihydroxyacetonephosphate

Pyridoxal phosphate

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Step-Growth PolymersStep-Growth Polymers• Step-growth polymersStep-growth polymers are formed by reaction

between molecules containing two functional groups, with each new bond created in a separate step• in this section, we discuss three types of step-growth

polymers; polyamides, polyesters, and polycarbonates

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PolyamidesPolyamides• Nylon-66Nylon-66 was the first purely synthetic fiber

• it is synthesized from two six-carbon monomers

-H2O+

Hexanedioic acid(Adipic acid)

1,6-Hexanediamine(Hexamethylenediamine)

heat

n

Nylon-66(a polyamide)

O

HOOH

O

NN

ON

ON

H

HH

Hremove H2O

H

H

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PolyamidesPolyamides• the polyaromatic amide known as KevlarKevlar is also made

from aa aromatic dicarboxylic acid and an aromatic diamine

COHnHOCO O

N NH

HH

H

NHCNHCO O

-H2O

1,4-Benzenediamine(p-Phenylenediamine)

1,4-Benzenedicarboxylicacid

(Terephthalic acid)

nKevlar

(a polyaromatic amide)

+ heat

remove H2O

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PolyestersPolyesters• the first polyester involved polymerization of this

diacid and ethylene glycol

OCH3

OCH3O

O HO

OH

O

O

OO

-CH3OH

Poly(ethylene terephthalate)(Dacron, Mylar)

heat

n

1,2-Ethanediol(Ethylene glycol)

Dimethyl terephthalate

+

remove CH3OH

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PolycarbonatesPolycarbonates• Lexan, the most familiar polycarbonatepolycarbonate, is formed by

reaction between the disodium salt of bisphenol A and phosgene

+Na-O

CH3

CH3

O-Na+ Cl Cl

O

OCH3

CH3

O

O

-NaCl

Phosgene

+

Disodium salt of Bisphenol A

Lexan(a polycarbonate)

n

remove Na+Cl-

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End End Chapter 18Chapter 18

Chapter 18Chapter 18

18 18-1 © 2003 thomson learning, inc. all rights reserved general, organic, and biochemistry, 7e...

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