AMINOALKANES (OR AMINES)
Introduction:
The IUPAC names for amines are aminoalkanes or alkanamines.
E.g.: CH3CH2NH2
 Ethylamine – amine –common name
 Aminoethane – aminoalkane – systematic name
 Ethanamine – alkanamine – systematic name
Mines all contain a nitrogen atom in the organic molecule. They occur widely
in nature and are used to manufacture local anaesthetics, sulfur drugs and
many other medicines.
Names and Classification:
Amines are organic derivatives of ammonia. They are classified as primary,
secondary or tertiary depending on the number of hydrogen atoms of the
ammonia that have been replaced by alkyl groups.
Primary amine – one alkyl group attached to N: R-NH2.
R-N -H
e.g. C2H5NH2 – aminoethane (ethylamine)
H
Secondary amine – two alkyl groups attached to N:
R-N -R
H
e.g. CH3NHCH3
N-methylaminomethane
(dimethylamine)
Tertiary amine – three alkyl groups attached to N:
R-N -R
R-NH-R
R-N(R*)-R
e.g. CH3CH2N(CH3)2
N,N-dimethylaminomethane
R*
Bonding and Physical Properties:
Intermolecular bonding in aminoalkanes results from:

Hydrogen bonds which form between the amino groups of neighbouring
molecules

Weak dipole-dipole forces which form between the hydrocarbon or alkyl
ends of neighbouring molecules.
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The low molecular mass aminoalkanes have relatively high melting and
boiling point due to hydrogen bonds, but the properties of larger aminoalkanes
are dominated by the alkyl groups and weak dipole-dipole interactions
Aminomethane and aminoethane are gases
Aminopropane and aminobutane are volatile liquids with an unpleasant ‘fishy’
smell.
The heavier aminoalkanes solids
The low molecular mass aminoalkanes are soluble in water due to hydrogen
bonding. Solubility in water decreases with molecular mass, as the alkyl
groups become larger.
Reactions of Primary Aminoalkanes:
Aminoalkanes are organic bases. They behave in a similar fashion to
ammonia, because of the lone pair of electrons on the nitrogen atom in
each molecule.
Like ammonia, aminoalkanes can act as:



Proton acceptors,
Nucleophiles, reacting with haloalkanes
Ligands, forming complex ions with transition metal ions
Water:
Soluble aminoalkanes form alkaline solutions. Aminoalkanes are more basic
than equimolar solutions of ammonia.
C2H5NH2(aq) + H2O(l)  C2H5NH3+(aq) + OH-(aq)
aminoethane
ethylammonium ion
Salt formation:
Aminoalkanes form stable, crystalline salts with mineral (inorganic) acids:
C2H5NH2(aq) + HCl  C2H5NH3+ClVolatile liquid
ethylammonium chloride
Non-volatile, water soluble ionic salt
Like ammonia, the vapours of aminomethane and aminoethane react with
concentrated hydrochloric acid fumes to produce an amine salt as a white
smoke:
LRY 2009
Haloalkanes:
Amines are nucleophiles, because like ammonia, they have a lone pair of
electrons on the nitrogen atom.
Primary aminoalkanes react with haloalkanes to form secondary
aminoalkanes.
E.g. aminomethane react with chloroethane to form N-methylaminoethane:
CH3NH2 + CH3CH2Cl
CH3NHCH2CH3 (+ HCl)
The hydrogen chloride released then reacts with basic aminomethane to form
methylammonium chloride:
CH3NH2 + HCl
CH3NH3Cl
The overall reaction is therefore:
2CH3NH2 + CH3CH2Cl
CH3NHCH2CH3 + CH3NH3Cl
Reaction Summary for Aminoethane:
C2H5Cl
N-ethylaminoethane
(C2H5)2NH
H2O
weakly alkaline
C2H5NH3+OHChloroethane
C2H5Cl
NH3(alc)
aminoethane
C2H5NH2
HCl
aminoethane
hydrochloride
C2H5NH3+Cl-
Cu2+(aq)
[Cu(C2H5NH2)4]2+
Deep blue solution
LRY 2009