The Claisen condensation first forms an enolate ion which undergoes a condensation reaction to give the beta-ketoester. This product immediately undergoes an acid-base reaction because its pKa is about 10 which is favored over the ester whose pKa is about 25.
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(A): Claisen Condensation involves the self condensation of ester molecules having $\alpha$ hydrogen. (R): Claisen condensation occurs in the presence of a strong base such as sodium ethoxide.
Propyne is first treated with sodium amide to generate a reactive intermediate A. This first reaction is a Brønsted acid-Brønsted base reaction. A is combined with benzyl bromide, giving product B, having molecular formula C10H10. Some pKa’s are provided to help you guess the structure of A. H3C—C≡C—H pKa > 40 pKa = 25 Na+ NH2- the conjugate acid of NH2- is NH3 which has pKa = 36 A Br B C10H10
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There are other condensation reactions similar to the aldol and Claisen condensations: a. The Perkin condensation is the condensation of an aromatic aldehyde and acetic anhydride. Give the product obtained from the following Perkin condensation.b. What compound would result if water were added to the product of the Perkin condensation? c. The Knoevenagel condensation is the condensation of an aldehyde or a ketone that has no $\alpha$ -hydrogens and a compound such as diethyl malonate that has an $\alpha$ -carbon flanked by two electron-withdrawing groups. Give the product obtained from the following Knoevenagel condensation. d. What product would be obtained if the product of the Knoevenagel condensation were heated in an aqueous acidic solution?
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