Hydrolysis of imines to give ketones (or aldehydes)

by James

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.


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.


  • 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.

{ 12 comments… read them below or add one }

Ivan December 7, 2012 at 6:07 pm

Great outline! Excellent helping me right before my exam!


Emily December 10, 2012 at 8:37 pm

Great review, but I’m a little confused as to where the fifth carbon went on the intramolecular imine hydrolysis under examples?


james December 11, 2012 at 4:43 pm

It’s a typo. Fixed – thanks for spotting it!


Dani March 31, 2013 at 8:52 pm

Thanks this was really helpful!
Just one thing I’m still confused about… why can’t step 5 happen before step 4? Wouldn’t it be more favorable to deprotonate the oxygen first and then have the lone pair kick down and get rid of LG?


james March 31, 2013 at 9:03 pm

Sure… but what’s going to deprotonate it? : – )
This is done under slightly acidic conditions.
Compare O-H (pka about 15) with protonated carbonyl (pKa -2)


Karin January 12, 2014 at 1:19 pm

I’m not sure if this question belongs in this topic. But I’m just wondering is an iminium ion a stronger electrophile than an oxonium ion? It is in the Strecker synthesis, but I don’t exactly understand why.


manjoorahmed September 20, 2014 at 4:15 am

is it possible to get imine from cyanide by making the use of grignard reagent?


James September 23, 2014 at 11:24 am

Yes, but isolating the imine is not always very easy.


P. Naveen kumar April 4, 2015 at 6:22 am

Imines are not stable it will undergo hydrolysis to get carbonyl compounds


Alen September 2, 2015 at 8:30 am

I don’t quite get it. Isn’t H2O a better leaving group then NH3 or in other words, isn’t the latter a better nucleophile? Why does then reaction proceed towards the ketone? Just because water is in excess?
Thank you for the clarification in advance…


James September 2, 2015 at 10:36 am

Yes – the reaction is in equilibrium, but the high concentration of H2O pushes the reaction toward the hydrolysis product.


Alen September 3, 2015 at 3:04 am

Thank you for your fast reply. Let me just say that this site is exceptionally educational and helpful!


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