Describe the following giving the relevant chemical equation in each case:

1. Carbylamine reaction

2. Hofmann’s bromamide reaction.

1. When aliphatic aromatic primary amines are heated with chloroform (CHCl₃) and alcoholic KOH solution, they form isocyanides or carbylamines which are foul smelling substances. This reaction is called carbylamine reaction.

Due to their foul smell, isocyanides can easily be detected.

This reaction is a chemical test only for the primary amines as secondary and tertiary amines do not give positive reaction to this test.

The first step is dehydrohalogenation (removal of hydrogen halide from the substrate) of chloroform to give an intermediate dichlorocarbene. This electrophilic dichlorocarbene intermediate is very reactive and attacks the nucleophilic nitrogen of the primary amine. The elimination of the hydrochloric acid leads to the formation of isonitrile. Mechanism of the reaction is shown below:

2. In this reaction, primary amines are prepared by treating an amide with bromine in an aqueous or alcoholic solution of NaOH. The amine thus produced, have one carbon atom less than the parent amide. Here, the –CO group is removed from the amide. This reaction is known as Hoffman bromamide reaction.

When the –CO group is removed from the amide (-CONH₂), we get amine (-NH₂).