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Hydrolysis of imines to give ketones (or aldehydes)

Description: Treatment of imines with water leads to their hydrolysis back to aldehydes (or ketones) and an amine.

Notes: The reaction is assisted through the use of an acid catalyst.

Examples:

Notes: Note that the third example is intramolecular.

Mechanism: Protonation of the imine nitrogen (Step 1, arrows A and B) results in the formation of the iminium ion, which undergoes 1,2-addition by water (Step 2, arrows C and D). Transfer of a proton (Step 3, arrows E and F) followed by 1,2 elimination of ammonia (Step 4, arrows G and H) lead to an oxonium ion, which is then deprotonated to give the neutral ketone.

Notes:

  • Acid is helpful but not an absolute requirement for this reaction. Reasonable mechanisms can be drawn without acid.
  • The “Cl” here in H3O+ Cl- is completely unimportant, just meant to show a balance of charge for H3O+. Other counter ions such as Br-, HSO3-, etc. would work just as well.
  • Note that this is an equilibrium reaction and goes in this direction because of the large excess of water. It is the exact reverse of imine formation.
  • There are certainly other reasonable ways to draw proton transfer (Step 3) and other species besides H2O that could conceivably act as bases in the last step.