Chapter 17

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

Introduction

Carboxylic acids, another carbonyl containing functional group also anhydrides, esters, and amides

loss of H2O is commonality here

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

Carboxylic 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

Nomenclature

IUPAC namesFind the longest carbon chain that contains

the carboxyl group as the parent alkanedrop the final -ee and replace it by -oic acidoic acidcarboxyl group is carbon 1because the carboxyl carbon is understood

to be carbon 1, there is no need to give it a number

Nomenclature

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

Nomenclature

dicarboxylic acids have the suffix -dioic aciddioic acid and the parent contains both carboxyl groups

the numbers of the carboxyl carbons are not indicated

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)

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

Nomenclature

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)

Physical 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

Physical Properties

carboxylic acids have high boiling points these 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

Physical 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

Acidity of RCOOHThe hydrogen on the oxygen is acidicsubstituents of high electronegativity,

especially -OH, -Cl, and -NH3+, near the

carboxyl group increase the acidity

CH3COOH ClCH2COOH Cl2CHCOOH Cl3CCOOHFormula:

pKa:

Name:

Increasing acid strength2.86

Chloroaceticacid

0.70

Trichloroaceticacid

1.48

Dichloroacetic acid

Acetic acid4.76

Reaction With Bases

All carboxylic acids 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)

Ionization 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

Anhydrides

The anhydrideanhydride is two carbonyl groups bonded to the same oxygenThe most common are symmetrical but the

mixed anhydride may be made. to name an anhydride, drop the word "acidacid"

and add the word "anhydrideanhydride"

Acetic anhydrideCH3C-O-CCH3

O O

Esters

The esterester is a carbonyl group bonded to an -OR group esters names are derived from the names of the

parent carboxylic acids name the “R” 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)

Amides

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)

Amidesa 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

Amides

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

Fischer Esterification

one of the most commonly used preparations of esterscarboxylic acid reacted with an alcohol in the

presence of an acid catalyst

reversible

CH3C-OHO

H-OCH2CH3

H2SO4CH3COCH2CH3

OH2O

Ethanoic acid(Acetic acid)

++

Ethyl ethanoate(Ethyl acetate)

Ethanol(Ethyl alcohol)

Preparation of Amides If a carboxylic acid and an amine are mixed, an

acid-base reaction to form an ammonium salt results 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

+

Preparation 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

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

Hydrolysis of Esters esters hydrolyze 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

CH3COCH2CH3

O

H2OH+

CH3COHO

CH3CH2OH+ +

Ethyl acetate Acetic acid Ethanol

Hydrolysis of Esters hydrolysis of an ester using a hot aqueous base can

also work – but not a catalyst here! this reaction is often called saponificationsaponification, a

reference to its use in the manufacture of soaps the carboxylic acid formed reacts with hydroxide ion each mole of ester hydrolyzed requires one mole of

base

CH3COCH2CH3

ONaOH

H2OCH3CO-Na+

OCH3CH2OH

Sodiumhydroxide

+ +

Ethyl acetate Sodiumacetate

Ethanol

Hydrolysis of Amides amides require more vigorous conditions hydrolysis in hot aqueous acid is not catalytic 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

Hydrolysis 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

Phosphoric 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

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

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

Step-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

Polyamides 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

Polyamides 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

Polyesters 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

Polycarbonates 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-

End End Chapter 18Chapter 18

Chapter 18