Beckmann Rearrangement with mechanism

The Beckmann Rearrangement process is an organic reaction that is useful in changing an oxime to that of an amide under some acidic conditions. When Ketoximes on treatment with an acid catalyst undergo rearrangement to give N – substituted amides is known as Beckmann rearrangement.

Beckmann-Rearrangement-with-mechanism

Characteristics: 

  • Anionotropic rearrangement
  • Migration Carbon to electron deficient Nitrogen
  • R & R’ –Alkyl,Aryl or H & R, R’ = both Alkyl, two such amides formed as R’–CO–NHR + R–CO–NHR’
  • Catalyst – Acidic reagents are Conc. H2SO4, HCHO, SO2, PCl5, HMPA7, PPA, BF3, SOCl2, PhSO2Cl
  • The reaction have also been carried out photochemically.


This reaction involves the migration of a group from carbon to electron deficient nitrogen . It is found that , the migrating group is always anti to the oxime hydroxyl group . The migrating group approaches the nitrogen atom from the opposite side to the departing exveen Hence this reaction is highly stereospecific .



Mechanism: It involves initial attack of acidic reagent, the –OH group converts into a more easily leaving group as OH2 OPCl6, OSO2 OH, etc. Loss of the leaving group generates an electron deficient species, which is accompanied by migration of a group from adjacent carbon to the electron deficient nitrogen. Resulting iminocarbocation reacts with water to give an amide.

Beckmann-rearrangement-mechanism

Driving forceAs the migration occurs via anionotropic route from C to electron deficient N, it adds stability and releases electron deficiency on the N.

Evidences: From the reaction scheme, the mechanism seems to be intramolecular while it is not so as a whole. This is evidenced by various observed factors. The rearrangement occurs under following aspects :

i) The rearrangement occurs in some intermediate between oxime and amide.

ii) Migration step is intramolecular.

iii) Anion (–OH or –OX) migration is intermolecular.

Uses: It is used in various fields such as The industrial manufacture of nylon relies on the alkaline polymerization, textile, pharmaceutical etc. some of Applications are listed below

1. is used in the production of the monomer unit of Nylon 12.

2. It is used in the production of raw material for Nylon 6.

3. In developing Drug paracetamol was using Beckmann rearrangement at industrial level by Hoechst Celanese.

4. It is also used for the production of benazepril, ceforanide, olanzapine, etazepine, enprazepine etc.

The industrial manufacture of nylon relies on the alkaline polymerization of a cyclic amide known trivially as caprolactam. Caprolactam can be produced by the action of sulfuric acid on the oxime of cyclohexanone in a rearrangement known as the Beckmann rearrangement.

FAQ Of Beckmann Rearrangement 

1. What is Beckmann Rearrangement ?


Beckmann rearrangement reaction is one of the important reactions which is treatment on ketoximes with an acid catalyst to N-Substituted Amide.  Ernst Otto Beckmann was a German Chemist who discovered the Beckmann rearrangement reaction. This is the reason the reaction is named after him and known as Beckmann rearrangement reaction.


2. Which group migrates in the Beckmann rearrangement?


In the Beckmann rearrangement of unsymmetrical ketones there are two groups that could migrate. There are also two possible geometrical isomers of an unsymmetrical oxime: C=N double bonds can exhibit cis/trans isomerism just as C=C double bonds can. When mixtures of geometrical isomers of oximes are rearranged, mixtures of products result, but the ratio of products mirrors exactly the ratio of geometrical isomers in the starting materials—the group that has migrated is in each case the group trans to the OH in the starting material

3. What is Caprolactam ?

The industrial manufacture of nylon relies on the alkaline polymerization of a cyclic amide known trivially as caprolactam. Caprolactam can be produced by the action of sulfuric acid on the oxime of cyclohexanone in a rearrangement known as the Beckmann rearrangement.

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