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Topic 4.7

AMINES


Preparation of primary, secondary and tertiary amines
Basic properties of amines
Uses of quaternary ammonium salts























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PREPARATION OF AMINES

Amines can be prepared in two ways: by nucleophilic substitution of a haloalkane and by
reduction from nitriles. The preparation from a haloalkane results in a mixture of primary,
secondary and tertiary amines and their salts. The preparation from a nitrile results in the
formation of primary…

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So primary amines are formed by the addition of excess ammonia to a haloalkane:

RX + 2NH3 RNH2 + NH4+X

Eg






Primary amines will also be formed if haloalkanes and ammonia are mixed in a 1:1 ratio. In this
case HCl is likely to be the second product as the…

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iii) tertiary amines

If any haloalkane is present after the secondary amine has been formed, it can be attacked by
the secondary amine to form a tertiary amine:





So tertiary amines are formed by reacting haloalkanes and ammonia in a 3:1 ratio or by
reacting a haloalkane with a secondary…

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So quaternary ammonium salts can be made by reacting haloalkanes and ammonia in a 4:1
ratio or by reacting tertiary amines and haloalkanes in a 1:1 ratio.

4RX + NH3 [R4N]+X + 3HX
R1X + R2R3R4N [R1R2R3R4N]+X

Eg





b) preparation of primary amines from nitriles

Primary amines can be made…

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BASIC PROPERTIES OF AMINES

Amines are weak bases the lone pair of electrons on the nitrogen atom can behave as a proton
acceptor. The strength of amines varies, but all react with strong acids to make alkylammonium
salts.

a) Reaction of amines with acids

Amines react with acids in the…

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The hydrogen atom is slightly more electropositive than the carbon atom. This means that the
carbon atom has a slight surplus of electrons which the nitrogen atom can attract towards itself.
This effect is known as a "positive inductive effect" and it means that the N atom has an excess…

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USES OF QUATERNARY AMMONIUM SALTS

Quaternary ammonium salts are principally used as cationic surfactants. Longchain ammonium
salts are mainly used for this purpose:

Eg





A surfactant is a substance which can be added to a liquid to reduce its surface tension.

Cationic surfactants can also be added to solids which…

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4. Summary of preparation and acidbase properties of amines

Type of reaction Mechanism

1. haloalkane primary amine Nucleophilic
substitution (required)
reagents: haloalkane and excess ammonia
conditions: heat
equation: RX + 2NH3 RNH2 + NH4X
or
reagent: haloalkane and ammonia (1:1 ratio)
conditions: heat
equation: RX + NH3 RNH2 + HX…

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equations: R1NH3Cl + NaOH R1NH2 + NaCl + H2O
R1R2NH2Cl + NaOH R1R2NH + NaCl + H2O
R1R2R3NHCl + NaOH R1R2R3N + NaCl + H2O


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