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Question #43971

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The Question

Compound $\mathbf{X}$ is $4$ -(methyl $\beta$ -D-glucopyranosyloxy)benzaldehyde. It is reacted with excess $\ce{HCHO}$ in the presence of $50\% \text{ NaOH (aq)}$ at $363\text{ K}$ . The reaction mixture is then carefully neutralized to $\text{pH } 7$ , and the major aromatic product $\mathbf{Y}$ is isolated. Finally, $\mathbf{Y}$ is treated with Tollens' reagent ( $\ce{[Ag(NH3)2]+}$ in aqueous ammonia). Which of the following correctly identifies the structure of $\mathbf{Y}$ and the observation for the Tollens' test?

Options

A.
$\mathbf{Y}$ is $4$ -(methyl $\beta$ -D-glucopyranosyloxy)benzyl alcohol; No silver mirror is formed.
B.
$\mathbf{Y}$ is $4$ -(methyl $\beta$ -D-glucopyranosyloxy)benzoic acid; No silver mirror is formed.
C.
$\mathbf{Y}$ is $4$ -( $\beta$ -D-glucopyranosyloxy)benzyl alcohol; A silver mirror is formed.
D.
$\mathbf{Y}$ is $4$ -(methyl $\beta$ -D-glucopyranosyloxy)benzyl alcohol; A silver mirror is formed.

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Cannizzaro Mechanism|Tollens vs. Fehling Specificity|Reducing Sugar Criteria

Why This Question Is Tricky

Common Mistakes

This problem tests two critical hidden variables in advanced organic chemistry.

First, the regioselectivity of the Cross-Cannizzaro reaction: students often forget that the more electrophilic formaldehyde acts exclusively as the hydride donor (getting oxidized), forcing the other aldehyde to be reduced.

Second, the 'anomeric locking' of glycosides: students frequently see a sugar moiety (polyol) and reflexively assume it will give a positive Tollens' test (reducing sugar).

However, a methyl glycoside is an acetal, which is completely inert to the strongly basic conditions of the Cannizzaro reaction and Tollens' reagent.

The trap exploits the assumption that alkaline conditions might deprotect the sugar or that the polyol itself is susceptible to mild oxidation.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Aldehydes, Ketones, and Carboxylic Acids - Class 12
Concept	Cannizzaro Mechanism
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free