Beckmann

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Beckmann

  1. 1. Beckman rearrangement Beckman rearrangement
  2. 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. 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. 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. 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. 6. Possible Isomers  2, p-bromophenyl ethyloxime is an asymmetric oxime, hence two possible products. OH HO N N CH3 CH3 Br Br
  7. 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. 8. Beckman Rearrangement  Open Chain oxime gives an open chain amide  Cyclic oximes give lactam
  9. 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. 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. 11. Beckman Rearrangement R1 R2 OH R2 C C N N OH R1
  12. 12. R1 R2 R1 R2 C RCOCl C N NBeckman OH OClRearrangement -OCl -Mechanism R2In the presence of R1 R2 +Cacid chlorides/acid Chalides N N+ R1 H2 O + OH R2 OH2 R2 C C -H+ R2CO N H R1 N N R1 R1
  13. 13. R1 R2 R1 R2 C H+ C N NBeckmanRearrangement OH OH2+ -H2OMechanism R2In the presence R1 R2 +Cof strong acids C N N+ R1 H2O + OH R2 OH2 R2 C C -H+ R2CO N H R1 N N R1 R1
  14. 14. Cyclic oxime
  15. 15. Application  Amides can also be prepared from the Beckmann Rearrangement Because it is an acid catalyzed rearrangement of an oxime to an amide

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