Write the mechanism of the following reaction:
`nBuBr +KCNoverset(EtOH-H_(2)O)rarr nBuCN`

Explanation

Given reaction is
n-Butyl Bromide + `KCN overset("EtOH" , H_(2)O)(to)` n-butyl cyanide
`CH_(3) - CH_(2) - CH_(2) - CH_(2) - Br overset(KCN)underset(EtOH , H_(2)O)(to) CH_(3) - CH_(2) - CH_(2) - CH_(2) - CN + KBr`
Mechanism :
Ionisation of KCN :
`KCN to K^(ox) + CN^(ox)`
`[: overset(Theta)(C) -= N :] larr rarr [: C = overset(..)(N)^(Theta) :]`
Resonance forms of `CN^(Theta)` ion.
`to CN^(Theta)` ion is an ambident nucleophile . It has the tendency to attack through C- atom (or) through N-atom . Attack through C-atom results cyanide product and attack through N-atom results isocyanide. But in presence of polar solvent KCN ionises and forms cyanide as major product .