Question

Explain Hoffmann bromamide degradation reaction and write the general equation for reaction involved.

Answer 1

• When amide is treated with $B{r}_2$ in aqueous or ethanolic solution of $NaOH$, degradation of amide results in formation of primary amine.
• Primary amine formed contains one carbon less than the number of carbon atoms in amide.

$O$

$R-\stackrel{||}{C}-N{H}_2+B{r}_2+4NaOH⟶R-N{H}_2+N{a}_{2}C{O}_3+2NaBr+2H_{2}O$

Mechanism:

• Base attacks amide deprotonating it and generating anion.
• Anion reacts with $B{r}_2$ forming bromoamide.
• Deprotonation of bromoamide occurs forming bromoamide anion which undergoes rearrangement forming isocyanate.
• Isocyanate forms carbamic acid by addition of $H_{2}O$ molecules.
• Decarboxylation of carbamic acid occurs forming primary amine.