Question

How will you convert nitromethane to methyl isocyanide ?

Hint:

Remember: \[ \text{Nitro Compound} \rightarrow \text{Primary Amine} \rightarrow \text{Isocyanide} \] Carbylamine reaction: \[ RNH_2 + CHCl_3 + 3KOH \rightarrow RNC + 3KCl + 3H_2O \] Only primary amines give a positive carbylamine test.

Answer 1

Concept: The conversion of nitromethane into methyl isocyanide cannot be achieved directly. First, the nitro group must be reduced to form a primary amine. The resulting primary amine is then converted into the corresponding isocyanide by the carbylamine reaction. Thus, the conversion is carried out in two major steps:

• Reduction of nitromethane to methylamine.

• Conversion of methylamine to methyl isocyanide by the carbylamine reaction.

Step 1: Reduction of nitromethane to methylamine. Nitromethane contains a nitro group \((-NO_2)\). On reduction using reducing agents such as \[ H_2/Ni,\quad Sn/HCl,\quad Fe/HCl \] the nitro group is converted into an amino group. The reaction is \[ CH_3NO_2 \xrightarrow[\text{}]{Sn/HCl} CH_3NH_2 \] Thus, nitromethane is converted into methylamine.

Step 2: Conversion of methylamine into methyl isocyanide. Methylamine is a primary amine. Primary amines on heating with chloroform and alcoholic potassium hydroxide undergo the carbylamine reaction to produce isocyanides. The reaction is \[ CH_3NH_2 + CHCl_3 + 3KOH \rightarrow CH_3NC + 3KCl + 3H_2O \] The product formed is methyl isocyanide.

Step 3: Writing the complete conversion sequence. The overall conversion is \[ CH_3NO_2 \xrightarrow[\text{}]{Sn/HCl} CH_3NH_2 \xrightarrow[\text{alc. }KOH]{CHCl_3} CH_3NC \]

Step 4: Justification of the method. Nitromethane itself does not undergo direct conversion to isocyanide. The nitro group must first be reduced to a primary amino group because the carbylamine reaction is given only by primary amines. Therefore, methylamine acts as the necessary intermediate in the conversion.

Final Conversion: \[ \boxed{ CH_3NO_2 \xrightarrow[\text{}]{Sn/HCl} CH_3NH_2 \xrightarrow[\text{alc. }KOH]{CHCl_3} CH_3NC } \]