Nitriles are organic compounds that have the general formula RCN (RC≡N).
Nitriles can be prepared by a substitution reaction using KCN.
The –:C≡N: ion is a good carbon nucleophile, and this substitution results in extension of the carbon chain.
It should also be noted that this reaction of nitriles is limited to preparation of amines where the NH2 group is also bonded to a CH2 group.
Reactions 1 and 2 can be combined to convert a haloalkane to a primary amine having an additional carbon atom.
It is important to note that
Nitriles can be prepared by a substitution reaction using KCN.
The –:C≡N: ion is a good carbon nucleophile, and this substitution results in extension of the carbon chain.
Reaction 1: CH3CH2Br + –:C≡N: 
CH3CH2C≡N: + Br–
The nitrile functional group contains a polar multiple bond and is converted on reduction with LiAlH4 to –CH2NH2. CH3CH2C≡N: + Br–| Reaction 2: CH3CH2C≡N | LiAlH4  | CH3CH2CH2NH2 |
It should also be noted that this reaction of nitriles is limited to preparation of amines where the NH2 group is also bonded to a CH2 group.
It is important to note that
in order to be prepared in this way, the primary amine must have a CH2 group adjacent to the NH2.
the overall outcome is replacement of Br (or another halide) by the CH2NH2 group.
the overall outcome is replacement of Br (or another halide) by the CH2NH2 group.