Chemistry 2100

Chapter 19

Carboxyl Derivatives In this chapter, we 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

RCNH2O

RC-OHO

H-OCR'O

RC-OHO

H-OR' RC-OHO

H-NH2

A carboxylic ac id An esterAn anhydride An amide

-H2O -H2O -H2O

acyl [ acetyl = Ac: R = CH3 ]

NR2

OR'

ClOH carboxylic acid

acid chlorideanhydrideesteramide

Y = O CO R'

O

CR Y

Esters The functional group of an ester is a carbonyl group bonded to an -OR group. R may be alkyl or aryl. –  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 -ic acid by -ate. –  A cyclic ester is called a lactone.

Ethyl ethanoate(Ethyl acetate)

Diethyl pentanedioate(Diethyl glutarate)

CH3COCH2CH3 O OOO

OO

A five-memberedlactone

O

O

CR Y

+ YH

O

CR Z

+ H Z

O

CR Y

+ YH

O

CR Z

+ H Zδ+ δ+ δ-

δ-

O

CR Y

+ YH

O

CR Z

+ H Zδ+ δ+ δ-

δ-

O

CR Y

+ YH

O

CR Z

+ H Zδ+ δ+ δ-

δ-

O

CR Y

+ YH

O

CR Z

+ H Z

OR' δ+ δ+ δ-

δ-

O

CR Y

+ YH

O

CR Z

+ H ZOR'

OR' δ+ δ+ δ-

δ-

O

CR Y

+ YH

O

CR Z

+ H ZOR'

OR' δ+ δ+ δ-

δ-

OH

O

CR Y

+ YH

O

CR Z

+ H ZOR'

OR' δ+ δ+ δ-

δ-

OH

OH

Fischer esterification

O

CR Y

+ YH

O

CR Z

+ H ZOR'

OR' δ+ δ+ δ-

δ-

OH

OH

H+

Hydrolysis of Esters

CH3COCH2CH3

OH2O

H+CH3COH

OCH3CH2OH+ +

Ethyl acetate Acetic acid Ethanol

Saponification

CH3COCH2CH3

ONaOH

H2O CH3CO-Na+O

CH3CH2OHSodium

hydroxide

+ +

Ethyl acetate Sodiumacetate

Ethanolheat

Properties of Esters

octyl acetate orange ethyl butyrate pineapple

methyl anthranilate grape coumarin clover methyl salicylate wintergreen

OH

methyl anthranilate grape

C OCH3

O

NH2 NH2

O

O

C

C

C

O

O

O

CH2

CH

CH2

O(oleic)

(linoleic)

(myristic)

Triglycerides & Waxess

waxes

Reaction with Amines •  Esters react with ammonia and with 1° and 2°

amines to form amides.

OCH2CH3

O

+ NH3 NH2

O

+ CH3CH2OHEthyl 2-phenyl acetate 2-Phenylacetamide

Amides The functional group of an amide is a carbonyl

group bonded to a nitrogen atom. –  To name an amide, drop the suffix -oic acid from

the IUPAC name of the parent acid, or -ic acid from its common name, and add -amide.

–  If the amide nitrogen is also 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)2O

N-Methylacetamide(a 2° amide)

Acetamide(a 1° amide)

N,N-Dimethylformamide(a 3° amide)

•• ••

R'

R"C N

O

R• •

•• ••

• •

R'

R"C N

O

R

•• ••

R'

R"C N

O

R• •

•• ••

• •

R'

R"C N

O

R

•• ••

R'

R"C N

O

R• •

•• ••• •

R'

R"C N

O

R

•• ••

R'

R"C N

O

R• •

•• ••• •

R'

R"C N

O

R

•• ••

R'

R"C N

O

R• •

•• ••• •

R'

R"C N

O

R

Amides A cyclic amide is called a lactam.

– The penicillins are referred to as β-lactam antibiotics.

O

NH

O

NHA four-membered lactam

(a β-lactam)A seven-membered lactam

α

β

NCH3

NH2

OHO

NHO

S

CH3COOH

The penicillinsdiffer in the groupbonded to thecarbonyl carbon

The β-lactam ring

Amoxicillin

Preparation 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

+

Preparation of Amides

•  It is much more common, however, to prepare amides by treating an anhydride with an amine.

CH3C-O-CCH3

O OH2NCH2CH3 CH3C-NHCH2CH3

OCH3COH

O+ +

Acetic anhdyride An amide

Anhydrides

The functional group of an anhydride 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 "acid" from the name of the carboxylic acid from which the anhydride is derived and add the word "anhydride”.

Acetic anhydrideCH3C-O-CCH3

O O

Reaction with Alcohols

Anhydrides react with alcohols and phenols to give an ester and a carboxylic acid.

Aspirin is prepared by the reaction of salicylic acid with acetic anhydride.

CH3COCCH3

O OHOCH2CH3 CH3COCH2CH3 HOCCH3

O+ +

Acetic anhydride Ethyl acetat e Acetic acidEthanol

O

COOH

OH CH3C-O-CCH3O COOH

OCCH3O

CH3C-OHAcetic an hydride

Acetylsalicylic acid(Aspirin)

Salicylic acid

+Acetic acid

+O O

Phosphoric Anhydrides The functional group of a phosphoric 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 OHHO-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

ATP

Adenosine Triphosphate

Polyamides Nylon-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)

OHO OH

ON N

ON

ON

H

HH

Hremove H2O

H

H

Polyamides The polyaromatic amide known as Kevlar is made from an aromatic dicarboxylic acid and an aromatic diamine.

COHnHOCO O

N NH

HH

H

NHCNHCO O

-H2O1,4-Benzenediamine

(p-Phenylenediamine)1,4-Benzenedicarboxylic

acid(Terephthalic acid)

nKevlar

(a polyaromatic amide)

+ heat

remove H2O

Polyesters The first polyester involved polymerization of this diester and diol.

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 polycarbonate, is formed by reaction between the disodium salt of bisphenol A and phosgene.!

+Na-OCH3

CH3

O-Na+ Cl Cl

O

OCH3

CH3

O

O

-NaCl

Phosgene

+

Disodium salt of Bisphenol A

Lexan(a polycarbonate)

n

remove Na+Cl-