Hofmann bromamide degradation of benzamide gives product aniline (A), which upon heating with CHCl3 and NaOH gives product benzene isocyanide (B), by carbylamine reaction. Hofmann bromamide degradation method is for preparation of primary amines by treating an amide with bromine in an aqueous or ethanolic solution of sodium hydroxide. The amine formed contains one carbon less than that present in the amide.
Aliphatic and aromatic primary amines on heating with chloroform and ethanolic potassium hydroxide form isocyanides or carbylamines which are foul smelling substances.
Note Secondary and tertiary amines do not show this reaction. This reaction is known as carbylamine reaction or isocyanide test and is used as a test for primary amines.