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.
Nomenclature of amides
Nomenclature of amides
Preparation of Amides
Carboxylic acidsAcid chlorides
Preparation of Amides
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.
Preparation of Amides
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