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Hofmann Rearrangement
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The conversion of amide to an amine with one carbon atom less by the action of alkaline hypohalite (NaOX or KOX) or bromine in alkali is known as Hofmann Rearrangement Reaction.

Hofmann Rearrangement Reactions

A rearrangement reaction is an organic reaction in which an atom, ion, group of atoms, or chemical unit migrates from one carbon atom to another carbon atom in the same or different molecule resulting in a structural isomer of the original molecule. The reaction often includes the breaking and/or making of carbon-carbon sigma bonds.

Types of rearrangement reactions.

Rearrangements are divided into two types,

a. Intramolecular rearrangement – Intramolecular rearrangements are those where the rearrangement of a group occurs within the molecule.

b. Intermolecular rearrangement – Intermolecular rearrangements are those where the rearrangement of a group occurs in the different molecules.

What is the Hofmann rearrangement reaction? What is Hofmann bromamide reaction? Illustrate Hofmann bromamide reaction ncert.

Principle of Hofmann rearrangement reaction

The conversion of amide to an amine with one carbon atom less by the action of alkaline hypohalite (NaOX or KOX) or bromine in alkali is known as Hofmann Rearrangement Reaction or Hofmann bromamide reaction.

This involves a rearrangement reaction of an N-haloamide into an isocyanate which hydrolyses rapidly, under the conditions of the reaction, into a primary amine. Because of the intermediate rearrangement, the reaction is also termed Hofmann haloamide rearrangement.

General Reaction

Hofmann Rearrangement Reaction, Hofmann Bromamide Reaction.

MechanismHofmann rearrangement reaction

The reaction takes place in three steps.

Step I:- Formation of N- bromoamide

In the first step alkali (potassium hydroxide) reacts with halogen ( Bromine) forming hypohalite (KOBr = Potassium hypo bromide). This potassium hypo bromide reacts with amide forming N – bromoamide, this is also called Hofmann bromoamide reaction.

Formation of N- bromamide in Hofmann Rearrangement Reaction
Formation of N- bromamide

Step II:-  Formation of isocyanate

In the second step, N- bromoamide reacts with alkali forming potassium halite which eliminates Br to give Nitrene, which is highly unstable.  Hence rearrangement takes place with the migration of the ‘R’ (alkyl or aryl) group to the electron-deficient ‘N’ atom called Isocyanate.

Formation of Isocyanate in Hofmann Rearrangement Reaction
Formation of Isocyanate

In aryl amides i.e., when the migrating group is aryl then the rate of Hofmann rearrangement gets increased by the presence of electron-releasing substituents in the para position of the aromatic ring.

In the cross-over experiment of Hofmann rearrangement, no cross-products are obtained when two different amides are rearranged then it is obvious that the rearrangement is intramolecular, and the migrating group never completely separates during the migration.

Step III:- Formation of Amine

In the third step, the isocyanate forms get reacted with an alkali-forming amine

Formation of Amine in Hofmann Rearrangement Reaction
Formation of Amine

The Curtius rearrangement is a similar well-known reaction.

Application of Hofmann Rearrangement Reaction

1)  Preparation of aliphatic primary amine.

Hofmann Rearrangement is one of the most important rearrangement reactions used in the synthesis of amine. Hofmann Rearrangement is used in the preparation of aliphatic primary amine from amide. Large quantities of aliphatic amines are generally made synthetically using this method.

aliphatic primary amine
Aliphatic primary amine

2) Preparation of aromatic primary amine

Hofmann Rearrangement is also used in the preparation of aromatic primary amine. Benzamide by using Hofmann rearrangement gives m-bromoaniline.

Preparation of Aromatic amine using Hofmann rearrangement reaction
Aromatic amine

3) Preparation of anthranilic acid

Anthranilic can be prepared using the Hofmann Rearrangement reaction.

Anthranilic acid preparation using Hofmann rearrangement reaction
Preparation of Anthranilic acid

4) Preparation of heterocyclic amine

Hofmann rearrangement reaction is used to prepare 3-amino pyridine from Nicotinamide, which is an important raw material in pharmaceutical industries and an Intermediate colorant. It is also used as a monomer in the polymer industry.

You can also read the Beckman Rearrangement reaction for a better understanding of the mechanism with electron-deficient N atoms.

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Who discovered the Hofmann Bromamide reaction?

The Hofmann Bromamide reaction was discovered by famous German chemist August Wilhelm von Hofmann (8 April 1818 – 5 May 1892) and hence is named after him.  He was awarded by Royal Medal in 1854 and the Copley Medal in 1875.

What is Hofmann Bromamide reaction with example ncert?

The conversion of amide to an amine with one carbon atom less by the action of alkaline hypohalite (NaOX) or bromine in alkali is known as Hofmann Rearrangement. In this N – bromoamide is formed which finally converts to amine hence this is also called the Hofmann bromoamide reaction. Examples are mentioned in the application.

What is Hofmann bromamide degradation reaction ncert ?

Hofmann developed the method for the preparation of primary amines. In this reaction, migration of an alkyl or aryl group takes place from the carbonyl carbon of the amide to the nitrogen atom. The amine so formed contains one carbon less hence the reaction is also called as Hofmann degradation reaction.
than that present in the amide

How is methylamine prepared from the Hofmann Bromamide reaction?

We can prepare Methylamine by Hofmann’s bromamide reaction using Acetamide.
CH3−CO−NH2 + Br2 + 4NaOH → CH3−NH2 + Na2CO3 + 2NaBr + 2H2O

What is meant by amide and amine?

Amide – An organic compound containing the group —CONH2, derived from ammonia by replacement of a hydrogen atom with an acyl group. General Formula as R-CONH2 . Example Benzamide ph-CONH2.
Amine – An organic compound containing the group —NH2, derived from ammonia by replacement of a hydrogen atom with an alkyl or aryl group. General Formula as R-NH2. Example Ethylamine (C2H5NH2).

What are Nitrenes in chemistry?

Nitrenes are sextet, highly reactive molecular species with the monovalent nitrogen atom, which can exist in a singlet or a triplet state.

What Is Hofmann Rearrangement Reaction?

The conversion of amide to an amine with one carbon atom less by the action of alkaline hypohalite (NaOX or KOX) or bromine in alkali is known as Hofmann Rearrangement Reaction.

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