StemCET Logo

Chemistry Question 68 – JEE-MAIN 2025

← Back
The major product (P) in the following reaction is : \ Ph-C(=O)-CHO \xrightarrow{\text{KOH, } \Delta} \text{ P (Major Product)}

The reactant, phenylglyoxal (Ph-CO-CHO), is an α-keto aldehyde, and the conditions (KOH, Δ) indicate a strong base and heat.

🥷
Ninja Strategy•Disproportionation Principle

The Cannizzaro reaction is a disproportionation, meaning one part of the molecule is oxidized and another is reduced. Only option 2 correctly shows both an oxidation (aldehyde to carboxylate) and a reduction (ketone to alcohol) within the same molecule.

Step 1: Identify Reactant and Reaction Type✦ Active

The reactant is phenylglyoxal (Ph-CO-CHO), which is an α-keto aldehyde. It lacks α-hydrogens on both the aldehyde carbon and the ketone carbon adjacent to the aldehyde. The reagents are KOH and heat (Δ), which are conditions for a Cannizzaro reaction.

Step 2: Apply Intramolecular Cannizzaro Reaction○ Expand

Phenylglyoxal undergoes an intramolecular Cannizzaro reaction. In this specific type of disproportionation, the more reactive aldehyde group is oxidized to a carboxylate, and the ketone group is reduced to an alcohol.

Ph-C(=O)-CHO→KOH, ΔPh-CH(OH)-COO⁻K⁺
💡 Teacher's Secret Hint

Remember that the aldehyde carbonyl is generally more electrophilic and thus more susceptible to initial nucleophilic attack by hydroxide.

Step 3: Determine the Major Product○ Expand

Following the intramolecular Cannizzaro mechanism, the aldehyde carbon (-CHO) is oxidized to a carboxylate (-COO⁻), and the ketone carbon (-CO-) is reduced to a secondary alcohol (-CH(OH)-). Therefore, the major product is potassium mandelate, Ph-CH(OH)-COO⁻K⁺.

✦ STEM Console utilizes AI models to generate step-by-step explanations and math clues. AI can make mistakes.