AMINES
Amines are considered to be derivatives of ammonia, in which one or more of
the hydrogen atoms in the ammonia molecule have been replaced by an alkyl
group.
Replacement of one H atom of ammonia with an alkyl group produces a
PRIMARY AMINE replacement of two H atoms produces a SECONDARY
AMINE replacement of all three H atoms results in a TERTIARY AMINE.
H—N—H
R—N—H
|
|
|
|
H
H
H
R’’’
Ammonia
Primary Amine
R-N—R’
R—N—R”
Secondary Amine Tertiary Amine
Amines are found in many biological molecules, including AMINO ACIDS, and
VITAMINS, and are used in the manufacture of pharmaceuticals such as
Sulfa drugs and anesthetics. The synthetic fibre, NYLON, is an amine
derivative.
THE NAMING OF AMINES:
The IUPAC names of amines are formed by adding the prefix amino- to the
corresponding alkane name of the amine. As usual, numbers are used to
indicate the carbon to which the amine substituent is attached. The
functional group takes priority over the alkyl group.
CH3-NH2
CH3 – CH – CH2 – CH – CH2 – CH3
aminomethane
|
|
CH3
NH2
3-amino-5-methylhexane
aminobenzene
For secondary or tertiary amines, the naming uses the “N” to indicate alkyl
groups attached directly to the nitrogen.
CH3 – CH – CH2 – CH – CH3
|
CH3
|
-N-CH2-CH3
\
CH2-CH3
NH – CH3
N-methyl-2-amino-4-methylpentane (2O)
N,N-diethylaminobenzene
QUESTIONS
1. Name and classify the following amines.
a) NH2 – CH2 – CH2 – CH – CH3
b)
|
NH2
NH2
NH2
c) NH – CH2 – CH2 – CH2 – CH – CH – CH3
|
|
d)
CH3–CH2-CH2-NH–CH2–CH3
CH3 CH3
2. Draw the structural formulas of four amines that have the molecular
formula C3H9N (two primary, one secondary, and one tertiary amine). Classify
the amines and name them.
PROPERTIES OF AMINES
1. Amines have an unpleasant odours. (the odour of decaying fish is
attributed to simple amines).
2. Because of the hydrogen bonding amines have higher BP than
hydrocarbons of similar molar mass. Since a nitrogen—hydrogen bond is less
polar than an oxygen—hydrogen bond, the hydrogen bonding in primary
amines is weaker than in alcohols of related formulas. As a result, the boiling
points of amines are lower than those of the related alcohols.
3. Amines are weak bases. Amines have a relatively high solubility in water
because of the hydrogen bonding that occurs in primary and secondary
amines. Tertiary amines do not hydrogen bond.
REACTIONS
Ammonia reacts with alkyl halides to produce an amine.
CH3-Cl
+ NH3
Chloromethane ammonia

CH3NH2
+
aminomethane
HCl
hydrogen chloride
If the aminomethane is reacted with more chloromethane a secondary amine
will be created.
Questions
3. Find the products in a reaction between chloroethane and 1-aminobutane.
4. Arrange the following molecules from lowest BP to the highest: ethanol,
ethanal, aminoethane, propane.