Question

Ester containing $\alpha$ -hydrogens undergo self condensation in presence of a strong base such as sodium ethoxide to form $\beta$ -ketoesters. This reaction is called

• A. Aldol condensation
• B. Claisen condensation
• C. Diekmann condensation
• D. Crossed-Claisen condensation

Answer 1

Answer: (B)

Ester containing $\alpha$ -hydrogens undergo self condensation in presence of a strong base such as sodium ethoxide to form $\beta$ -ketoesters. This reaction is called Claisen condensation.

$C{H}_3-\stackrel{O}{\stackrel{||}{C}}-O{C}_2{H}_5+H-\stackrel{\alpha }{C}{H}_{2}COO{C}_2{H}_5\stackrel{C_2{H}_5{O}^{-}N{a}^{+}}{\to }\underset{\left(A\beta \text{-keto ester}\right)}{C{H}_3-\stackrel{O}{\stackrel{||}{C}}-\stackrel{\alpha }{C}{H}_{2}COO{C}_2{H}_5}+C_2{H}_{5}OH$

Crossed-Claisen condensation is feasible only when one of the reactants has no $\alpha$ -hydrogen and is thus incapable of undergoing self condensation. For example