Identify the product in the following reaction: cyclobutyl chloride $\underset{\text{(ii) H2O/HCl, }\mathrm{\Delta }}{\overset{\text{(i) KCN}}{\to }}\underset{\text{(iv) H2O}}{\overset{\text{(iii) Br2/red P}}{\to }}$ Product.

Solution & Explanation

\textbf{Answer:} (D) Cyclobutane bearing $-\mathrm{COOH}$ and an alpha $-\mathrm{Br}$ (alpha-bromocyclobutanecarboxylic acid) \textbf{Solution:} Step (i): $\mathrm{KCN}$ replaces $-\mathrm{Cl}$ to give cyclobutyl cyanide. Step (ii): acidic hydrolysis converts the nitrile to cyclobutanecarboxylic acid $-\mathrm{COOH}$. Steps (iii)-(iv): $\mathrm{Br}{}_2$/red P is the Hell-Volhard-Zelinsky reaction, which alpha-brominates the acid; aqueous work-up gives the alpha-bromo acid carrying both $-\mathrm{COOH}$ and an alpha $-\mathrm{Br}$.