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.


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 '17 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 '17 at 4:15
  • $\begingroup$ Why enolate formation requires acidic medium although the base is attacking the hydrogen? $\endgroup$
    – Suraj S
    Apr 27 '17 at 4:24
  • $\begingroup$ @SurajS A base is a good nucleophile and tends to attact the carbonyl carbon directly $\endgroup$ Apr 27 '17 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 '17 at 4:43

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