Beckmann Rearrangement
Session Objectives
By the end of this
session, students will be able to:
• Steps involved in Beckmann rearrangement
• Mechanism of Beckmann rearrangement
PREPARATION OF BENZANILIDE FROM BENZOPHENONE (BECKMANN
REARRANGEMENT)
• Aldehydes and ketones react with hydroxyl amines in the
presence of sodium hydroxide to give an Oxime of low melting point (alpha or
syn aldoxime).
• It rapidly rearranges to give an isomeric Oxime of higher
melting point by acids-(beta or anti aldoxime).
• Oximes of ketones undergo Beckmann rearrangement to
substituted amides under the influence of variety of acidic reagents e.g HCOOH,
PCl5, H2SO4, SOCl2, etc.
• In this rearrangement, the migrating group is always anti-
to –OH group and thus this reaction is stereo specific.
• Here benzophenone oxime in presence of PCl5 rearranges
to benzanilide.
Step involved in Beckmann Rearrangement
Reaction:
Step-I: Preparation of benzophenone oxime
Step-II:
Preparation of benzanilide from benzophenone oxime
Mechanism of Beckmann Rearrangement
MECHANISM: – Step-I: Preparation of benzophenone oxime
Step-II: Preparation
of benzanilide:
Summary
• Aldehydes and ketones react with hydroxyl amines in the
presence of sodium hydroxide to give an Oxime of low melting point (alpha or
syn aldoxime).
• This is stable in alkali but rapidly rearranges to give an
isomeric Oxime of higher melting point by acids-(beta or anti aldoxime).
• Oximes of ketones undergo Beckmann rearrangement to
substituted amides under the influence of variety of acidic reagents e.g HCOOH,
PCl5, H2SO4, SOCl2, etc.
• In this rearrangement, the migrating group is always anti-
to –OH group and thus this reaction is stereo specific.
• Here benzophenone oxime in presence of PCl5 rearranges to
benzanilide.