Master Organic Chemistry Reaction Guide

Claisen Condensation of esters

Description: When esters are treated with strong base, an enolate can be formed. The resulting enolate can add to another ester, resulting in a substitution at the carbonyl carbon.
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9 thoughts on “Claisen Condensation of esters

    1. I believe the reversibility depends on the type of base you are using and not the number of the alpha hydrogens.

      Here are some common bases for the irreversible forms:
      NaH, NaNH2, KH, LDA

      Common reversible bases:
      NaOEt, NaOMe

  1. is there any possibility of dickmann reaction if -NH- group present in molecule?
    i think -NH- group give anion instead of -CH2-.

  2. Since the b-keto ester has an acidic proton, does the reaction of ester with base need to be followed by a work-up step?

  3. why hydroxide ion (HO–) would lead to hydrolysis of the ester?
    is not supposed formation of enolate is acid base reaction and it is faster from addition reaction?

    1. Two issues. 1) The choice of base is usually the conjugate base of the solvent. Hydroxide ion is the conjugate base of water. Water is not going to dissolve most substrates you want to use in this reaction.
      2) Even if you use, say, 1-2 equivalents of KOH in ethanol or methanol in solvent, equilibrium will result in formation of KOR as the active base since it’s present in vast excess.
      3) Acid-base reactions on heteroatoms (O-H, N-H, S-H) tend to be faster than addition reactions. Not sure I’d say the same applies with formation of an enolate, which does require significant reorganization of the molecule (i.e. rehybridization of the alpha carbon).
      4) Why take the chance? You’re putting your time, effort and energy into a procedure. Why take even the slightest chance in decreasing your yield, when it costs you basically nothing to use alkoxide as a base instead of KOH?

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