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Which one of the following on reduction with lithium aluminium hydride yields a secondary amine?
A
Methyl isocyanide
B
Acetamide
C
Methyl cyanide
D
Nitroethane
Detailed Solution
Reduction of alkyl isocyanides in the presence of $LiAlH_4$ yields secondary amines containing methyl as one of the alkyl groups.
$R-N\equiv C + 4[H] \xrightarrow{LiAlH_4} R-NH-CH_3$ ($2^\circ$ amine)
For methyl isocyanide: $CH_3-N\equiv C + 4[H] \xrightarrow{LiAlH_4} CH_3-NH-CH_3$ (dimethylamine)
The carbon of the isocyanide group is attached to nitrogen, so after reduction it becomes a methyl group on nitrogen, giving a secondary amine.
Alkyl cyanides give $1^\circ$ amines on reduction: $CH_3-C\equiv N + 4[H] \rightarrow CH_3CH_2NH_2$
Acetamide also gives a primary amine: $CH_3CONH_2 + 4[H] \rightarrow CH_3CH_2NH_2 + H_2O$
Nitroethane gives the primary amine $CH_3CH_2NH_2$.
So the compound that yields a secondary amine is methyl isocyanide.
$R-N\equiv C + 4[H] \xrightarrow{LiAlH_4} R-NH-CH_3$ ($2^\circ$ amine)
For methyl isocyanide: $CH_3-N\equiv C + 4[H] \xrightarrow{LiAlH_4} CH_3-NH-CH_3$ (dimethylamine)
The carbon of the isocyanide group is attached to nitrogen, so after reduction it becomes a methyl group on nitrogen, giving a secondary amine.
Alkyl cyanides give $1^\circ$ amines on reduction: $CH_3-C\equiv N + 4[H] \rightarrow CH_3CH_2NH_2$
Acetamide also gives a primary amine: $CH_3CONH_2 + 4[H] \rightarrow CH_3CH_2NH_2 + H_2O$
Nitroethane gives the primary amine $CH_3CH_2NH_2$.
So the compound that yields a secondary amine is methyl isocyanide.