Question

Write the mechanism of the following reaction:

$nBuBr+KCN\stackrel{EtOH-H_{2}O}{\to }nBuCN$

Answer 1

$\text{Mechanism of given reaction}$

The given reaction is an $S_{N}2$ reaction. In this reaction, $C{N}^{-}$ acts as a nucleophile and attacks the carbon atom to which $Br$ is attached. $C{N}^{-}$ ion is an ambident nucleophile and can attack through both $C$ and $N$ atoms.

In this case, $C{N}^{-}$ attacks through the $C$-atom because in polar protic solvents ($EtOH$ in this case), more electronegative atom site (Nitrogen atom) will be solvated to a greater extent via $H$-bonding and hence, $C$-atom is now available to attack $n$-Butyl bromide and produces $n$-Butyl cyanide.