In this modification of Knoevenagel condensation, malonic acid (not the ester) is reacted with an aldehyde to yield an alpha beta conjugated carboxylic acid. Pyridine is used as a solvent and catalyst, while beta-alanine (or some other amino acid) is used as a co-catalyst.
1. Can you please explain the use of beta-alanine? Is it used as a H+ source, or something else?
2. Why can malonic acid be reacted in V-D modification, while only its ester can be reacted in standard Knoevenagel condensation conditions?
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1) Yes , beta-alanine is the proton source in this reaction and provides the proton to pyridine (OR BASE) hence converting into conjugate acid, which then reacts with the malonic ester.
2) V-D modification uses malonic acid in place of the conventional ester ...
This solution explains the mechanisms of a modification of Knoevenagel condensation.