The Beckmann reaction produces the rearrangement of an oxime into an amide. This reaction is carried out in an acid medium.

beckmann transposition 01

Step 1. Protonation of the hydroxyl group
beckmann transposition 02

Stage 2. Migration of the substituent with simultaneous loss of water.

beckmann transposition 03


Stage 3. Attack of the water on the cation

beckmann transposition 04


Stage 4. Formation of iminol by loss of a proton from water

beckmann transposition 05


Stage 5. Iminol tautomerism

beckmann transposition 06


In the case of oximes from aldehydes (aldoximes), chain migration occurs, making it impossible to obtain unsubstituted amides.

The Beckmann rearrangement requires the ANTI arrangement of the migrating group with respect to the water molecule acting as the leaving group.

The Beckmann rearrangement produces lactams by reaction with cyclic oximes.

beckmann transposition 08