I don't know if this question is kind of vague. But i was wondering like in the reaction of saponification of ester, where you have a base like OH- directly attacking the carbonyl carbon, can you also have a base like OH- attack the carbonyl carbon atom and then protonate the O- atom to create like a hydrate? Or does the base prefer attack hydrogen of alpha carbon of ketone and aldehyde? I am kind of confused about when a enol is create and when a hydrate is created since both of them can be formed by a base. So, hence I ask this question.


1 Answer 1


Ester hydrolysis and the soap-making process

In aqueous solution, esters are subject to hydrolysis to the corresponding carboxylic acid and alcohol components:


Hydrolysis is, the reverse of the esterification reaction. The addition of base accelerates ester hydrolysis because the nucleophile is a hydroxide ion, which is much more reactive than a water molecule.


Enol formation

The a-protons of carbonyls, are somewhat acidic, because the negative charge on the conjugate base is stabilized by resonance with the carbonyl oxygen. In the formation of an enol, a base abstracts an a-proton from a carbonyl compound, and that same proton (or a proton on a nearby acid group) is transferred to the carbonyl oxygen. The deprotonated form of an enol is an enolate.


However in this scenario I don't think an enolate will form in this case.

  • enol formation is favored in acidic environments rather than basic

The preffered route would be the first one above.


To avoid a bit confusion:

  • To avoid generalisation, the R1 group given on the ester can be anything from -C(CH2)3, in this case 2 alpha carbons and no alph hydrogen. (No enol possible)

  • an alpha hydrogen may be there but reaction conditions won't favour enol formation.

Hope this clears doubts

  • 1
    $\begingroup$ Thanks for the response. But which compound do you mean by "no alpha proton on the carbon adjacent to the carbonyl group" Ester, aldehyde and ketone all have alpha carbon. $\endgroup$
    – TLo
    Apr 26, 2017 at 22:11
  • $\begingroup$ @TLo, esters do form enols but, this hydrolysis reaction there wouldn't be an enol intermediate, due to reasons mentioned. These are typically seen in aldol addition reaction $\endgroup$ Apr 27, 2017 at 4:15
  • $\begingroup$ Why enolate formation requires acidic medium although the base is attacking the hydrogen? $\endgroup$
    – Suraj S
    Apr 27, 2017 at 4:24
  • $\begingroup$ @SurajS A base is a good nucleophile and tends to attact the carbonyl carbon directly $\endgroup$ Apr 27, 2017 at 4:37
  • $\begingroup$ "Please not that I am making reference to the above reaction only (hydrolysis of esters). Some compounds can form enols in both mediums however, I am trying not to overgeneralise* $\endgroup$ Apr 27, 2017 at 4:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.