19 19-1 © 2006 thomson learning, inc. all rights reserved general, organic, and biochemistry, 8e...

1919

19-1© 2006 Thomson Learning, Inc.All rights reserved

General, Organic, General, Organic, and Biochemistry, 8eand Biochemistry, 8e

Bettelheim, Brown,Bettelheim, Brown,

Campbell, & FarrellCampbell, & Farrell

1919


IntroductionIntroduction• 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

RCNH2

O

RC-OHO

H-OCR'O

RC-OHO

H-OR' RC-OHO

H-NH2

A carboxylic acid An esterAn anhydride An amide

-H2O -H2O -H2O

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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). Your book does not discuss how to name the mixed anhydrides so you will not be responsible for being able to name a mixed anhydride.

• 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 anhydride

CH3C-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 -oateoate.

• A cyclic ester is called a lactonelactone.

Ethyl ethanoate(Ethyl acetate)

Diethyl pentanedioate(Diethyl glutarate)

CH3COCH2CH3 O O

OO

O

O

A five-memberedlactone

O

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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 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)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

Cephalexin (Keflex)(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 Fischer EsterificationEsterification• Fischer esterificationFischer esterification is the most

commonly used preparation of esters (Chapter 18).• In Fischer esterification, a carboxylic acid is reacted with an alcohol in the presence of an acid catalyst, such as concentrated sulfuric acidCH3C-OH

OH-OCH2CH3

H2SO4CH3COCH2CH3

OH2O

Ethanoic acid(Acetic acid)

++

Ethyl ethanoate(Ethyl acetate)

Ethanol(Ethyl alcohol)

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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, however, to prepare amides by treating an anhydride with an amine.

CH3C-O-CCH3

O OH2NCH2CH3 CH3C-NHCH2CH3

OCH3COH

O+ +

Acetic anhdyride An amide

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Hydrolysis of Hydrolysis of Anhydrides Anhydrides • HydrolysisHydrolysis is a chemical decomposition

involving breaking a bond and the addition of the elements of water.

• Carboxylic anhydrides, particularly the low-molecular- weight ones, react readily with water (hydrolyze) 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 hydrolyze 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+

O

CH3CH2OH

Sodiumhydroxide

+ +

Ethyl acetate Sodiumacetate

Ethanolheat

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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 hydrolyzed 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 hydrolyzed requires one mole of base.CH3CNH

ONaOH

H2OCH3CO-Na+

OH2N

AnilineSodiumacetate

Acetanilide

++heat

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Reaction with Reaction with AlcoholsAlcohols• 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 acetate Acetic acidEthanol

O

COOH

OH CH3C-O-CCH3

OCOOH

OCCH3

O

CH3C-OH

Acetic anhydride

Acetylsalicylic acid(Aspirin)

Salicylic acid

+

Acetic acid

+O O

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Reaction with AminesReaction with Amines• Anhydrides react with ammonia and with 1° and 2° amines to form amides.

• Two moles of amine are required; one to form the amide and one to neutralize the carboxylic acid by-product.

CH3C-O-CCH3

O O

+NH3

CH3CNH2

O

CH3C-OH

O

CH3C-OH

O+NH3

CH3C-O-CCH3

O O

+2NH3CH3CO- NH4

+

O

+

CH3CNH2

O

+

CH3CO- NH4+

O

Aceticanhydride

Acetamide Ammoniumacetate

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Reaction with AminesReaction with Amines• Esters react with ammonia and with 1° and 2° amines to form amides.

• Thus, an amide can be prepared from a carboxylic acid by first converting the carboxylic acid to an ester by Fischer esterification and then reaction of the ester with an amine.

OCH2CH3

O

+ NH3 NH2

O

+ CH3CH2OH

Ethyl 2-phenyl acetate 2-Phenylacetamide

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Reaction with AminesReaction with Amines• Amides do not react with ammonia or with amines.

• You have a quiz next class on amines. It is a very small amount of information with only two reactions, so be prepared to complete the reactions and be able to name the products.

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March Science NightMarch Science Night• For the remaining portion of class I want you to discuss what you will be doing for the March Science Night.

• Seniors: I need to know if you will be presenting on your senior project, doing a new project or being an assistant (helper) on the actual night.

• Juniors: I need to know what your project, talk or activity will be. You may work in groups of up to four students. If you are already doing a project for Mr. Isel you don’t have to do one for me. Next class I will be putting up a sign up sheet and a list from 1B to see if you want to join two projects.

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End End Chapter 19Chapter 19

Chapter 19Chapter 19

19 19-1 © 2006 thomson learning, inc. all rights reserved general, organic, and biochemistry, 8e...

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