3.3.11: Amines
Amines are a group of organics related to the ammonia compound (NH3). In amines, the hydrogens in
ammonia have been replaced by hydrocarbon groups.
Amines are given different classes based on how many hydrogens have been replaced.
• Primary – one hydrogen replaced. E.g., ethylamine.
• Secondary – two hydrogens replaced. E.g., di-ethylamine.
• Tertiary – three hydrogens replaced. E.g., tri-ethylamine.
Amines have high boiling points because they are able to hydrogen-bond. Primary amines have the highest
boiling points; those of secondary amines are slightly lower because the nitrogen lone pair is in the middle
of the chain, which slightly detracts from
the dipole effect. Tertiary amines are not
able to hydrogen-bond, so the boiling
points are much lower.
All small amines are soluble in water for
the same reason (including tertiary
amines, as they can use the hydrogen
from the water to form the bond). Larger
amines are not soluble because the
hydrogen-bonds between the water
molecules are stronger than those
between the amines.
Preparation
Primary aliphatic amines (containing chains, not rings) are formed from the reaction of ammonia with
halogenoalkanes.
Reactants: Ammonia, Halogenoalkane
Conditions: Heat with conc. ammonia in ethanol, in a sealed tube (not reflux).
Products: Amines, Amine salts.
Amines are a group of organics related to the ammonia compound (NH3). In amines, the hydrogens in
ammonia have been replaced by hydrocarbon groups.
Amines are given different classes based on how many hydrogens have been replaced.
• Primary – one hydrogen replaced. E.g., ethylamine.
• Secondary – two hydrogens replaced. E.g., di-ethylamine.
• Tertiary – three hydrogens replaced. E.g., tri-ethylamine.
Amines have high boiling points because they are able to hydrogen-bond. Primary amines have the highest
boiling points; those of secondary amines are slightly lower because the nitrogen lone pair is in the middle
of the chain, which slightly detracts from
the dipole effect. Tertiary amines are not
able to hydrogen-bond, so the boiling
points are much lower.
All small amines are soluble in water for
the same reason (including tertiary
amines, as they can use the hydrogen
from the water to form the bond). Larger
amines are not soluble because the
hydrogen-bonds between the water
molecules are stronger than those
between the amines.
Preparation
Primary aliphatic amines (containing chains, not rings) are formed from the reaction of ammonia with
halogenoalkanes.
Reactants: Ammonia, Halogenoalkane
Conditions: Heat with conc. ammonia in ethanol, in a sealed tube (not reflux).
Products: Amines, Amine salts.
