Question

For the reaction given below : 
The compound which is not formed as a product in the reaction is a : 
 

• A. diol
• B. dicarboxylic acid
• C. compound with both alcohol and acid functional groups
• D. monocarboxylic acid

Hint:

Cannizzaro reaction: \(2\text{R-CHO} \rightarrow \text{R-CH}_2\text{OH} + \text{R-COOH}\). If the substituent R contains other groups (like phenolic -OH), they remain intact. Only the aldehyde functionality changes.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The starting material is p-hydroxybenzaldehyde. Treatment with concentrated \(NaOH\) and heat, followed by acidification, indicates a Cannizzaro reaction. This reaction occurs in aldehydes that lack \(\alpha\)-hydrogens.
Step 2: Detailed Explanation:
In the Cannizzaro reaction, the aldehyde undergoes self-disproportionation (simultaneous oxidation and reduction):
1. One molecule of p-hydroxybenzaldehyde is reduced to p-hydroxybenzyl alcohol (\(HO-C_6H_4-CH_2OH\)). This molecule contains two hydroxyl groups (one phenolic and one benzylic), making it a diol.
2. Another molecule is oxidized to the salt of p-hydroxybenzoic acid (\(HO-C_6H_4-COO^-Na^+\)). Upon acidification (\(H_3O^+\)), it yields p-hydroxybenzoic acid (\(HO-C_6H_4-COOH\)).
- This acid is a monocarboxylic acid.
- It is also a compound with both alcohol (phenolic -OH) and acid functional groups.
Since there is only one aldehyde group per benzene ring, there is no pathway to generate a second carboxylic acid group on the same molecule.
Step 3: Final Answer:
A dicarboxylic acid is not formed in this process.