Hofmann Degradation of Amides | Hofmann Rearrangement

An unsubstituted amide is converted to primary amine in hofmann degradation. Carbonyl group of amide is completely eliminated and primary amine is given as the product. Due to remove of one carbonyl group, one carbon atom is eliminated from the amide compound.

Reaction Medium

This reaction should be done in alkali medium. sodium hypobromite (NaOBr) is the most used reagent for this reaction. Sodium hypobromite can be prepared by NaOH and Br₂ reaction. KOH and Br₂ are also used as reagents. . This reaction occurs in a special rearrangement mechanism.

Hofmann degradation gives primary amines | Amide to Amine

In this reaction, number of carbon atoms are reduced by one. Hence this reaction is a very important in organic conversion questions to produce a compound which have a less carbon atom than previous compound.

The R group may be alkyl or aryl.

R = -CH₃ , -CH₂CH₃ , -C₆H₅ (phenyl)

If alkyl group is so long

but if it is an alkyl group of more than about six or seven carbons, low yields are obtained. To gey higher yields Br₂ and NaOMe are used instead of Br₂ and NaOH.

Hofmann degradation of ethanamide

Hofmann degradation of ethanamide will give methanamine. Here, ethanamide reacts with Br₂ / KOH and give methamine (primary amine), KBr, K₂CO₃ and water as products.

Hofmann degradation of propanamide

Hofmann degradation of propanamide will give ethanamine as the primary amine. If Br₂ / NaOH is usedfor hofmann degradation, Na₂CO₃, NaBr and water are given as other products.

Hofmann degradation of benzanamide

Hofmann degradation of benzanamide will give aniline. This is one of the reaction aniline can be prepared without benzene.

Benzene to aniline is a two step reaction and benzanamide to aniline is only a single step in hofmann degradation.

Hofmann Rearrangement Mechanism

Isocyanate, is given as the actual product. But due to reaction condition, this isocyanate product hydrolysis to give primary amine.

References - Hofmann Rearrangement

MARCH’S ADVANCED ORGANIC CHEMISTRY, REACTIONS, MECHANISMS,AND STRUCTURE 6^{th edition, Michael B. Smith, Jerry March,
18-13 The Hofmann Rearrangement (p,1607)}