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Question #44498

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The Question

In an attempt to synthesize 2,5-hexanedione, a student subjects an aqueous solution of potassium 3-oxobutanoate to Kolbe electrolysis using smooth platinum electrodes at 298 K. However, the expected Kolbe dimerization product is obtained in negligible yield. Instead, the reaction is diverted through an alternative anodic process. Which of the following statements correctly identifies the primary reason for the failure of the standard Kolbe radical decarboxylation in this system?

Options

A.
The basic medium generated at the cathode facilitates enolate formation, which undergoes anodic oxidation at a significantly lower potential than the carboxylate moiety.
B.
The strong electron-withdrawing effect of the carbonyl group destabilizes the acyloxy radical, triggering a two-electron oxidation to a primary carbocation.
C.
The electrochemically generated $\beta$ -keto alkyl radical undergoes a rapid 1,2-hydride shift to form a thermodynamically stable $\alpha$ -keto radical.
D.
The $\beta$ -keto carboxylate salt undergoes rapid spontaneous thermal decarboxylation in the aqueous solution at 298 K, depleting the substrate.

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Kolbe’s Electrolysis Mechanism|Alpha-Hydrogen Acidity|Reaction Quotient vs. Equilibrium Constant

Why This Question Is Tricky

Common Mistakes

This problem tests the student's ability to evaluate competitive electrochemical pathways rather than blindly applying the Kolbe electrolysis pattern ( $R-COO^- \rightarrow R-R$ ).

The 'Hidden Variable' is the generation of a basic medium at the cathode, which interacts with the 'Chemical Exception'—the highly acidic $\alpha$ -hydrogens of the $\beta$ -keto salt.

Students often fail to recognize that enolates have significantly lower oxidation potentials than carboxylates.

Distractors target common misconceptions: Option B misapplies the Hofer-Moest (carbocation) pathway to a highly destabilized $\beta$ -keto system; Option C relies on a non-existent radical 1,2-hydride shift; and Option D confuses the thermal instability of $\beta$ -keto acids with their relatively stable carboxylate salts.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Hydrocarbons - Class 11 Part 2
Concept	Kolbe’s Electrolysis Mechanism
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free