Question

Give structures of A, B and C: $CH_3Cl \xrightarrow{KCN}$ A $\xrightarrow{LiAlH_4}$ B $\xrightarrow{CHCl_3 + \text{alc. } KOH, \Delta}$ C

Hint:

Carbylamine reaction ($CHCl_3$ + alc. $KOH$ + primary amine) ? Isocyanide (foul-smelling). This is a confirmatory test for $1^\circ$ amines.

Answer 1

Step 1: Concept
A series of organic reactions converting an alkyl halide to a compound with a new functional group at each step.

Step 2: Analysis
$CH_3Cl$ + $KCN$: The cyanide ion ($CN^-$) is a nucleophile. It displaces the chloride ($S_N2$) to give methanenitrile (acetonitrile), $CH_3CN$. This is compound

A.

Step 3: Analysis
$CH_3CN$ + $LiAlH_4$: $LiAlH_4$ is a powerful reducing agent that reduces nitriles ($-CN$) to primary amines ($-CH_2NH_2$). Product: methanamine ($CH_3NH_2$). This is compound

B.

Step 4: Analysis
$CH_3NH_2$ + $CHCl_3$ + alcoholic $KOH$, $\Delta$: This is the carbylamine (isocyanide) reaction, a characteristic test for primary amines. The product is methyl isocyanide ($CH_3NC$). This is compound

C.

Final Answer:
A: $CH_3CN$ (Ethanenitrile/Acetonitrile)
B: $CH_3NH_2$ (Methanamine/Methylamine)
C: $CH_3NC$ (Methyl isocyanide)