The Beckman rearrangement is an acid-catalyzed rearrangement of oximes to substituted amides or lactams. Oximes are compounds derived from aldehydes and ketones that contain a C=N-OH grouping. Ketoximes undergo the Beckman rearrangement in the presence of acids, yielding an acid-amide product through an intramolecular rearrangement. The reaction proceeds through a nitrilium ion intermediate formed by alkyl migration and hydroxyl group expulsion, followed by hydrolysis to form the final amide product.

1. Beckman rearrangement
Beckman
rearrangement

2. Oximes
 compounds, containing the grouping C
= N-OH, derived from aldehydes and
ketones by condensing them with
hydroxylamine
+
H
R2CO + NH2OH R2C=NOH

3. Types of Oximes
Oximes are of two types:
 Aldoxime: combination of aldehydes
with hydroxylamine.
 Ketoxime: Combination of ketones with
hydroxylamine.
RCHO + RHC=NOH
H
+ NH2OH
R2CO R2C=NOH

4. Chemical Properties
 The ketoximes by the action of acids
undergo a peculiar intramolecular re-
arrangement known as the BECKMAN
REARRANGEMENT yielding an acid-
amide or anilide as a final product.
 Named: German Chemist Ernst
Beckmann

5. Isomers
 If we use aldehydes or asymmetrical
ketones, there is the possibility of
getting TWO STEREOISOMERS of
the oximes.
OH HO
N N
R R' R R'

6. Possible Isomers
 2, p-bromophenyl ethyloxime is an
asymmetric oxime, hence two possible
products.
OH HO
N N
CH3 CH3
Br Br

7. Beckman Rearrangement
 It is an acid-catalyzed rearrangement
of an oxime to an N substituted amide
R1R2C == N - OH R2- CO - NR1
H
OR
R1- CO - NR2
H

8. Beckman Rearrangement
 Open Chain oxime gives an open chain
amide
 Cyclic oximes give lactam

9. Beckman Rearrangement
 The Beckmann solution, acetic acid,
hydrochloric acid and acetic anhydride,
is widely used to catalyze the
rearrangement
 Other acids, such as polyphosphoric
acid, sulfuric acid or phosphorous
pentachloride can also be used

10. Beckman Rearrangement
 The reaction mechanism of the
Beckmann rearrangement is generally
believed to consist of:
1. An alkyl migration (trans to –OH) with
expulsion of the hydroxyl group to form a
nitrilium ion
2. Followed by hydrolysis

11. Beckman Rearrangement
R1 R2 OH R2
C C
N N
OH R1

12. R1 R2 R1 R2
C RCOCl C
N N
Beckman OH OCl
Rearrangement -OCl -
Mechanism R2
In the presence of R1 R2
+C
acid chlorides/acid
C
halides
N
N+
R1
H2 O
+ OH R2
OH2 R2
C
C -H+
R2CO N H R1
N
N
R1
R1

13. R1 R2 R1 R2
C H+ C
N N
Beckman
Rearrangement OH OH2+
-H2O
Mechanism R2
In the presence R1 R2
+C
of strong acids
C
N
N+
R1
H2O
+ OH R2
OH2 R2
C
C -H+
R2CO N H R1
N
N
R1
R1

14. Cyclic oxime

15. Application
 Amides can also be prepared from
the Beckmann Rearrangement
Because it is an acid catalyzed
rearrangement of an oxime to an
amide