Question

Explain the mechanism of claisen-schmidt reaction.

Answer 1

Hint: Firstly it is important to know what is exactly the claisen-schmidt reaction. Then feasibility of the occurrence of the reaction, which in this case is great due to the achievement of greater aromaticity. Then this reaction is actually a cross aldol condensation and is completed in four steps.

Complete step by step answer:
The reaction between an aldehyde or ketone having an α-hydrogen with an aromatic carbonyl compound lacking an α-hydrogen is called the Claisen–Schmidt condensation. This is a reaction that yields aromatic aldehyde as the final product. Therefore the feasibility and the success rate is quite high in practical approach.
Reaction of acetaldehyde with benzaldehyde in presence of $NaOH$ . This reaction is a cross-aldol condensation reaction.
The entire process is conducted basically in four steps. It is completed in the following steps:
Step 1: The acetaldehyde is reacted in presence of base to get the negatively charged compound for further reaction.
$
  C{H_3} - CHO{ \to ^ - }C{H_2} - CHO \\
  (Acetaldehyde) \\
 $ in the presence of $NaOH$
Step 2: Then this compound is further reacted with benzaldehyde to yield a negatively charged aldehydic compound. This time with the aromatic ring.
$^ - C{H_2} - CHO + {C_6}{H_5} - CHO \to {C_6}{H_5} - CH{O^ - } - C{H_2} - CHO$
Step 3: Now this obtained compound is treated in acidic presence.
${C_6}{H_5} - CH{O^ - } - C{H_2} - CHO \to {C_6}{H_5} - CHOH - C{H_2} - CHO{\text{ in acidic presence }}{{\text{H}}^ + }$
Step 4: Entire compound is now heated such that the water molecule gets separated and the aromatic aldehyde is obtained.
${C_6}{H_5} - CHOH - C{H_2} - CHO \to {C_6}{H_5} = CH - CHO{\text{ when heated in high temperature}}$

Note: Quantitative yields in Claisen–Schmidt reactions have been reported in the absence of solvent using sodium hydroxide as the base plus benzaldehydes. This reaction is attainable due to the conversion of the product into a stable aromatic compound as the final product.