- Libermann's Nitroso
Primary, secondary and tertiary amines react differently with nitrous
Primary amines react with nitrous acid to give an alcohol. Secondary
amines react with nitrous acid to produce yellow oily nitrosoamines. The reaction takes place in cold
conditions. The yellow solution is then warmed with phenol and sulphuric acid to give a green coloured
solution. On adding water, the colour of the
solution changes to red. On adding sodium hydroxide the colour changes to greenish blue to violet. This
overall reaction is called the Libermann's nitroso reaction. This reaction is only given by
secondary amines. Tertiary amines dissolve in nitrous acid to give their
called alkyl amines. They are named by adding the suffix amine to the
name of the corresponding alkyl groups. The primary amine
is named as the amino derivative and are called aminoalkanes. The prefix amino is added to the name
of the parent alkane corresponding to the
parent alkane. The carbon atom containing the
amino group is given the lowest number. Secondary and tertiary amines
are named as N-alkyl aminoalkanes. Depending
upon the alkyl groups, they are named as N-alkyl or N,N-dialkyl amino alkanes. If
the alkyl groups are different then the largest alkyl group forms the
parent alkane and the smaller alkanes are the substituents.
In the IUPAC system, aliphatic amines are called alkanamines.
- Basicity of Amines
Amines have a pyramidal structure like ammonia.
The nitrogen atom is sp3 hybridised.
The nitrogen atom contains a lone pair which contributes to its basicity. In aliphatic amines, the alkyl group
attached is electron releasing which increases the electron density on
the nitrogen atom making it more basic. Thus, the alkyl amines are more
basic than ammonia. The basicity of alkyl amines
is in the order 3° amine > 2° amine > 1° amine. But it is observed
that the size of the alkyl group also affects the basicity.
More the size of the alkyl group less is the basicity.
This effect is called steric hindrance. Thus,
the strongest base among the amines is 2º amine.