The self condensation of aromatic aldehydes with no a-hydrogen in presence of cyanide ion as catalyst to a-hydroxy ketone is called :

Question

Accepted Answer

The self-condensation of aromatic aldehydes with no α-hydrogen in the presence of a cyanide ion as a catalyst to form α-hydroxy ketone is known as the Benzoin condensation. Let's explore why Option 3 is the correct answer and why the other options are incorrect:

1. **Benzoin Condensation (Option 3):** 
   - The Benzoin condensation is a well-known reaction where two molecules of an aromatic aldehyde, such as benzaldehyde, undergo a condensation reaction in the presence of a cyanide ion catalyst to form an α-hydroxy ketone, specifically benzoin. This reaction is characteristic of aromatic aldehydes that lack an α-hydrogen. The cyanide ion acts as a nucleophile, initiating the reaction by attacking the carbonyl carbon of the aldehyde, leading to the formation of the benzoin product. This perfectly matches the description given in the question.

2. **Stobbe Reaction (Option 1):**
   - The Stobbe reaction involves the condensation of aldehydes or ketones with esters of succinic acid to form unsaturated carboxylic acids. This reaction does not involve the formation of α-hydroxy ketones and does not use cyanide ions as a catalyst. Therefore, it does not fit the description provided in the question.

3. **Perkin Condensation (Option 2):**
   - The Perkin condensation is a reaction between an aromatic aldehyde and an anhydride in the presence of a base to form α,β-unsaturated carboxylic acids. This reaction is different from the Benzoin condensation as it does not involve the formation of α-hydroxy ketones and does not use cyanide ions as a catalyst. Hence, it is not applicable to the scenario described in the question.

4. **Cannizaro's Reaction (Option 4):**
   - The Cannizaro's reaction involves the disproportionation of non-enolizable aldehydes (aldehydes without α-hydrogens) in the presence of a strong base to yield an alcohol and a carboxylic acid. This reaction does not produce α-hydroxy ketones and does not involve cyanide ions. Therefore, it is not relevant to the process described in the question.

In conclusion, the Benzoin condensation is the only reaction among the options provided that involves the self-condensation of aromatic aldehydes with no α-hydrogen in the presence of a cyanide ion catalyst to form α-hydroxy ketones. This makes Option 3 the correct answer.