Hoffmann Bromamide Degradation: Mechanism & Examples | Chemca

Organic Chemistry

Hoffmann Bromamide Degradation: Mechanism & Examples

By Chemca Editorial Team • Last Updated: January 2026 • 9 min read

The Hoffmann Bromamide Degradation is a powerful method for the preparation of primary amines. It involves the treatment of a primary amide with bromine in an aqueous or ethanolic solution of sodium hydroxide. The unique feature of this reaction is that the amine product contains one carbon less than the starting amide.

1. General Reaction

A primary amide reacts with Bromine ($Br_2$) and strong alkali ($KOH$ or $NaOH$) to form a primary amine.

$$ R-CONH_2 + Br_2 + 4KOH \xrightarrow{\Delta} R-NH_2 + K_2CO_3 + 2KBr + 2H_2O $$

Key Features:

Step-Down Reaction: The carbonyl carbon is lost as carbonate, shortening the carbon chain by one.
Reagents: $Br_2$ + Alkali ($KOH/NaOH$).
Product: Primary Amine ($1^\circ$) only.

2. Detailed Mechanism

The reaction proceeds via the formation of an Isocyanate intermediate.

Step 1: Bromination of Amide

The base abstracts a proton from the amide, followed by reaction with bromine to form N-Bromoamide.

$$ R-CONH_2 + OH^- \rightarrow R-CONH^- + H_2O $$ $$ R-CONH^- + Br_2 \rightarrow R-CONHBr + Br^- $$

Step 2: Formation of Acyl Nitrene/Isocyanate

The base abstracts the remaining proton from the nitrogen. The resulting anion undergoes rearrangement (migration of alkyl group R from Carbon to Nitrogen) with the simultaneous loss of the bromide ion. This is the Rate Determining Step.

$$ R-CONHBr + OH^- \rightarrow R-CON^-Br + H_2O $$ $$ R-CON^-Br \rightarrow \underbrace{R-N=C=O}_{\text{Alkyl Isocyanate}} + Br^- $$

Step 3: Hydrolysis

The isocyanate is hydrolyzed by the base to form the primary amine and carbonate ion.

$$ R-N=C=O + 2OH^- \rightarrow R-NH_2 + CO_3^{2-} $$

3. Stereochemistry

Retention of Configuration

The migration of the alkyl/aryl group ($R$) from the carbonyl carbon to the nitrogen atom is strictly Intramolecular. If the migrating group is chiral, it migrates with complete Retention of Configuration.

4. Examples

A. Synthesis of Methylamine

Degradation of Acetamide ($2$ Carbons) gives Methylamine ($1$ Carbon).

$$ CH_3CONH_2 + Br_2 + 4KOH \rightarrow CH_3NH_2 + K_2CO_3 + 2KBr + 2H_2O $$

B. Synthesis of Aniline

Degradation of Benzamide.

$$ C_6H_5CONH_2 + Br_2 + 4KOH \rightarrow C_6H_5NH_2 \text{ (Aniline)} + \dots $$

5. Applications

Preparation of pure primary amines free from secondary/tertiary amines.
Descending the homologous series (converting higher acid derivatives to lower amines).
Synthesis of Anthranilic acid from Phthalimide.

Hoffmann Bromamide Quiz

Test your concepts on Amide degradation. 10 MCQs with explanations.

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