Synthesis Methods for Benzyl Isocyanide Preparation

To determine which reactions yield benzyl isocyanide ($\text{C}_6\text{H}_5\text{CH}_2\text{NC}$), let us analyze each of the given chemical reactions:

1. Reaction A: $\text{C}_6\text{H}_5\text{CH}_2\text{Br} + \text{AgCN} \longrightarrow \text{C}_6\text{H}_5\text{CH}_2\text{NC} + \text{AgBr}$

   • Mechanism: Silver cyanide ($\text{AgCN}$) is predominantly covalent in nature. As a result, the lone pair of electrons on the nitrogen atom acts as the nucleophile rather than the carbon atom.
   • Product: Reaction of benzyl bromide ($\text{C}_6\text{H}_5\text{CH}_2\text{Br}$) with $\text{AgCN}$ yields benzyl isocyanide ($\text{C}_6\text{H}_5\text{CH}_2\text{NC}$) as the major product.

2. Reaction B: $\text{C}_6\text{H}_5\text{CH}_2\text{NH}_2 + \text{CHCl}_3 + 3\text{NaOH} \longrightarrow \text{C}_6\text{H}_5\text{CH}_2\text{NC} + 3\text{NaCl} + 3\text{H}_2\text{O}$

   • Mechanism: This is the Carbylamine reaction (Isocyanide test). Primary amines react with chloroform ($\text{CHCl}_3$) in the presence of a base ($\text{NaOH}$) via a dichlorocarbene ($:\!\text{CCl}_2$) intermediate.
   • Product: Benzylamine ($\text{C}_6\text{H}_5\text{CH}_2\text{NH}_2$) is a primary amine and produces benzyl isocyanide ($\text{C}_6\text{H}_5\text{CH}_2\text{NC}$).

3. Reaction C: $\text{C}_6\text{H}_5\text{Br} + \text{AgCN} \longrightarrow \text{C}_6\text{H}_5\text{NC} + \text{AgBr}$

   • Product: Reaction of bromobenzene with $\text{AgCN}$ yields phenyl isocyanide ($\text{C}_6\text{H}_5\text{NC}$), not benzyl isocyanide.

4. Reaction D: $\text{C}_6\text{H}_5\text{NH}_2 + \text{CHCl}_3 + 3\text{NaOH} \longrightarrow \text{C}_6\text{H}_5\text{NC} + 3\text{NaCl} + 3\text{H}_2\text{O}$

   • Product: Aniline ($\text{C}_6\text{H}_5\text{NH}_2$) undergoes the carbylamine reaction to form phenyl isocyanide ($\text{C}_6\text{H}_5\text{NC}$), not benzyl isocyanide.

5. Reaction E: $\text{C}_6\text{H}_5\text{CH}_2\text{CH}_2\text{Br} + \text{KCN} \longrightarrow \text{C}_6\text{H}_5\text{CH}_2\text{CH}_2\text{CN} + \text{KBr}$

   • Product: Potassium cyanide ($\text{KCN}$) is ionic, so nucleophilic attack occurs through the carbon atom to yield a nitrile (cyanide), namely 3-phenylpropanenitrile ($\text{C}_6\text{H}_5\text{CH}_2\text{CH}_2\text{CN}$).

Thus, A and B Only produce benzyl isocyanide.

Correct Answer: A and B Only (Option A)