Hofmann Rearrangement | What Is Hofmann Rearrangement Reaction| Hofmann Reaction kya hai?
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
Mechanism – Hofmann 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.
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.
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
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.
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.
3) Preparation of anthranilic acid
Anthranilic can be prepared using the Hofmann Rearrangement reaction.
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.
Some important and Useful Articles
Mass spectroscopy is an instrumental method of structure determination. It gives information about the structure and molecular weight of the sample.
A molecule is bombarded with high energy electrons about 70 eV which leads to fragmentation. Mass spectra give exact molecular weight it also indicates hours the molecule breaks into fragments that can be recognized. Read More…
A polymer may be defined as a high molecular weight compound formed by the combination of small molecules of low molecular weight.
The small unit of which polymer is made is known as a monomer.
FAQs
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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