Question

Reaction between benzaldehyde and acetophenone in presence of dilute NaOH is known as:

• A. Aldol condensation
• B. Cannizzaro's reaction
• C. Cross Cannizzaro's reaction
• D. Cross Aldol condensation

Answer 1

The Correct Option is D

The question asks for the name of the reaction that occurs between benzaldehyde and acetophenone in the presence of dilute NaOH. Let's examine the options and determine the correct answer:

1. Aldol condensation: This reaction typically involves aldehydes or ketones with at least one α-hydrogen atom reacting in the presence of a base to form β-hydroxy aldehydes or ketones (aldol products). This reaction cannot occur between benzaldehyde and acetophenone alone because benzaldehyde lacks an α-hydrogen.
2. Cannizzaro's reaction: This occurs when aldehydes without α-hydrogens (like formaldehyde) react with a strong base, resulting in disproportionation into an alcohol and a carboxylic acid. However, this does not apply here since we are using both benzaldehyde and acetophenone.
3. Cross Cannizzaro's reaction: This is a variation of the Cannizzaro reaction involving a mixture of aldehydes where one undergoes oxidation and the other reduction. Since one of the compounds (acetophenone) does have α-hydrogens, this reaction is irrelevant.
4. Cross Aldol condensation: In this reaction, two different starting carbonyl compounds (one with α-hydrogens and one without) react in the presence of a base, like NaOH. Benzaldehyde (no α-hydrogens) and acetophenone (with α-hydrogens) can participate in such a reaction.

The correct answer is Cross Aldol condensation. This is because acetophenone, which has α-hydrogen atoms, can provide the enolate ion in the presence of NaOH, reacting with benzaldehyde to form the final product.

Conclusion: Hence, the reaction between benzaldehyde and acetophenone in the presence of dilute NaOH is known as Cross Aldol condensation.