Question

Butane nitrile can be prepared by heating?
A) Propyl alcohol with KCN
B) Butyl chloride with KCN
C) Butyl alcohol with KCN
D) Propyl chloride with KCN.

Answer 1

Hint : This reaction is an example of substitution reaction in which the -CN group or the cyanide ion replaces the halogen present in the haloalkane and forms the final product.

Complete answer :
When haloalkanes are supplied with heat, under reflux with a solution of sodium or potassium cyanide in presence ethanol, the halogen is replaced by a -CN group and the respective nitrile is formed as a result. Here, heating under reflux essentially means heating the flask with a condenser placed vertically in order to prevent loss of volatile substances coming out from the mixture. We should also note that the solvent has a very significant role in this reaction.
The chemical formula for Butane nitrile is given as ${{C}_{3}}{{H}_{7}}CN$. It is a colourless liquid that is soluble with polar organic solvents. When propyl chloride ${{C}_{3}}{{H}_{7}}CN$ is heated in the presence of KCN it forms nitrile with propyl. We can write the reaction as follows:
${{C}_{3}}{{H}_{7}}Cl+KCN\to {{C}_{3}}{{H}_{7}}CN+KCl$
We can write the same reaction in ionic form as:
${{C}_{3}}{{H}_{7}}Cl+C{{N}^{-}}\to {{C}_{3}}{{H}_{7}}CN+C{{l}^{-}}$

Additional Information:
KCN or Potassium cyanide is a crystalline solid with a white or colourless appearance. It has a faint odour of almonds due to the cyanide ion. KCN is one of the most toxic and potent poison. It decomposes slowly in the air by absorbing the atmospheric moisture to release toxic hydrogen cyanide gas.

The correct option is (B).

Note : This reaction can be performed using any of the halogens, such as bromine, iodine, fluorine. It should be taken care that no water molecules are present, else the substitution will be replaced by -OH instead of -CN.