Which amongst the following reaction of alkyl halides produces isonitrile as a major products? (A)…
Which amongst the following reaction of alkyl halides produces isonitrile as a major products?
(A) $\mathrm{R}-\mathrm{X}+\mathrm{HCN} \rightarrow$
(B) $\mathrm{R}-\mathrm{X}+\mathrm{AgCN} \rightarrow$
(C) $\mathrm{R}-\mathrm{X}+\mathrm{KCN} \rightarrow$
(D) $\mathrm{R}-\mathrm{X}+\mathrm{NaCN} \underset{\mathrm{H}_2 \mathrm{O}}{\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}}$
Choose the most appropriate answer from the options given below
(B) only
(A) and (B) only
(D) only
(C) and (D) only
Solution
$\mathrm{KCN}$ is predominately ionic and provides cyanide ions in solution. Although both carbon and introgen atoms are in a position to donate electron pairs, the attack takes place mainly through carbon atom and not through nitrogen atom since $\mathrm{C}-\mathrm{C}$ bond is more stable than $\mathrm{C}-\mathrm{N}$ bond. However, AgCN is mainly covalent in nature and nitrogen is free to donate electron pair forming isocyanide as the major product
$\mathrm{R}-\mathrm{X}+\mathrm{AgCN} \longrightarrow \mathrm{R}-\mathrm{NC}+\mathrm{AgX}$