Imines, Oximes, and Hydrazones

Formation of Imines

• Start with an aldehyde or ketone.
• Add an amine.
• Use an acid catalyst.
• Forms an imine:
  • If Y = H or an alkyl group, it is called an imine.
  • If Y = OH, it is called an oxime.
  • If Y = NH₂ or NH with an additional alkyl group, it is a hydrazone.

Reversibility

• To convert back to the original aldehyde or ketone:
  • Increase the concentration of water with an acid catalyst.
  • Example: Hydrolysis of an imine returns cyclohexanone and a primary amine.

Formation of Oximes

• Start with cyclohexanone and hydroxylamine, with an acid catalyst.
• Product: Oxime (Oxygen and imine combined).
• Stability due to resonance between nitrogen and oxygen.
  • Oximes are more stable than imines.

Resonance Structure

• Lone pair on oxygen can stabilize the partially positive carbon.

Asymmetrical Ketones

• Can produce two stereoisomers.
• Oximes are easier to isolate than imines.

Formation of Hydrazones

• Start with cyclohexanone and hydrazine.
• Product: Hydrazone.
• Stability similar to oximes, due to resonance.

Example with 2,4-Dinitrophenylhydrazine (2,4-DNP)

• Reacts with cyclohexanone forms a hydrazone.
• Diagnostic test for aldehydes or ketones.
• Historically used for structure determination.