chapter 8 amide

NURUL’ AIN BINTI JAMION

AMIDES

ORGANIC CHEMISTRY II

CHM301

INTRODUCTION The functional group:

Amides are derived from carboxylic acids. A carboxylic acid contains the -COOH

group, and in an amide the -OH part of that group is replaced by an -NH2 group.

Primary amides are named by changing the name of the acid by dropping the -oic acid or -ic acid endings and adding -amide.

Nomenclature of amides

Secondary amides are named by using an upper case N to designate that the alkyl group is on the nitrogen atom.

Tertiary amides are named in the same way.


Preparation of Amides

Carboxylic acidsAcid chlorides


Carboxylic acids The carboxylic acid is first converted into an

ammonium salt which then produces an amide on heating.

The ammonium salt is formed by adding solid ammonium carbonate to an excess of the acid. For example, ammonium ethanoate is made by adding

ammonium carbonate to an excess of ethanoic acid.

When the reaction is complete, the mixture is heated and the ammonium salt dehydrates producing ethanamide.


Acid chlorides In the first stage, the ammonia reacts with the

ethanoyl chloride to give ethanamide and hydrogen chloride gas.

Then the hydrogen chloride produced reacts with excess ammonia to give ammonium chloride.

…and you can combine both equation to give one overall equation:

Reactions of amides

1. Hydrolysis2. With nitrous acid3. Reduction4. Hoffmann degradation5. Dehydration

Reactions of amides

1. Hydrolysis Acidic

Used: concentrated acid (HCl/H2SO4).Products:

ammonium or ammonium salt and carboxylic acid

Example:

1. Hydrolysis Acidic

General equation:

Reactions of amides

C

O

R NH2

H3O+ + HClreflux

C

O

R OH + NH4+

Cl-

NR'

HC

O

R N

+ H3O+ reflux

C

O

R OH

+ HR''

R''

R'

Reactions of amides

1. Hydrolysis Alkaline

Used: concentrated sodium hydroxide solution.

Products: ammonia or an amine and carboxylate salt

Example:

Reactions of amides

1. Hydrolysis Alkaline

General equation:

C

O

R NH2

+ OH- reflux

C

O

R O-

+ NH3

C

O

R + OH- reflux

C

O

R O-

+ NH

N

R'

R''

R'

R''

Reactions of amides2. With nitrous acid Amides reacts with nitrous acid (HNO2) to give carboxylic acid and N2

gas. Nitrous acid (HNO2) is unstable and is prepared in situ by the reaction

of dilute HCl or dilute H2SO4 with sodium nitrite in the absence of heat.

NaNO2 (s) + HCl (aq) → NaCl (aq) + O=N-OH (aq)

nitrous acid

R-CONH2 + HNO2 R-COOH + N2(evolved)+H2O

2. With nitrous acid

R C

O

NH2 N2R C

O

OHHNO2

CH3 C

O

NH2 N2CH3 C

O

OHHNO2

EXAMPLE

amide carboxylic acid

ethanoic acidethanamide

Reactions of amides

Reactions of amides3. Reduction

Amides, RCONR'2, can be reduced to the amine, RCH2NR'2 by conversion of the C=O to -CH2-

Amides can be reduced by LiAlH4 but NOT the less reactive NaBH4

Reactions of amides3. Reduction

Look at the N substituent in the following examples (those bonds don't change!)

Reactions of amides

4. Hoffmann degradation Hofmann degradation is a reaction between

an amide and a mixture of bromine and sodium hydroxide solution. Heat is needed.

The net effect of the reaction is a loss of the -CO- part of the amide group. You get a primary amine with one less carbon atom than the original amide had.

The general equation:

∆

4. Hoffmann degradation Example:

Ethanamide methylamine full equation for the reaction is:

The Hofmann degradation is used as a way of cutting a single carbon atom out of a chain.

Reactions of amides

Reactions of amides

5. Dehydration Amides are dehydrated by heating a solid

mixture of the amide and phosphorus(V) oxide, P4O10 / phosphorus oxychloride, POCl3 .

Water is removed from the amide group to leave a nitrile group, -CN. The liquid nitrile is collected by simple distillation.

For example, with ethanamide, you will get ethanenitrile.

CHEMICAL TESTS TO DIFFERENTIATE BETWEEN CARBOXYLIC ACID DERIVATIVES

ACYL CHLORIDE ESTER AMIDE

Water Vigorous. White fumes

(HCl) liberated.

No reaction No reaction

Acid hydrolysis

Vigorous, RCOOH formed

Reversible, produces

RCOOH and alcohol

Form RCOOH and

ammonium salt

Base hydrolysis

Vigorous, salt of

RCOOH form

Non reversible,

forms carboxylate

salt and alcohol

Ammonia gas liberated

Ammonia Forms amide Form amide No reaction

Reduction No reaction Forms two alcohols

Forms amine

Hoffman degradation

No reaction No reaction Forms amine

chapter 8 amide

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