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Question #44797

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The Question

Consider the bifunctional dicarboxylic acid derivative, 4-nitrophthaloyl dichloride ( $\mathbf{X}$ ). The reduction of $\mathbf{X}$ to 4-nitrophthalaldehyde using Lithium tri-tert-butoxyaluminum hydride (LTBA, denoted as $\mathbf{R}$ ) in THF at 195 K proceeds via a mechanism where the transfer of the first hydride equivalent is the rate-determining step (RDS) with a bimolecular rate constant $k$ .

In an independent experiment, $\mathbf{X}$ is treated with $Sn/HCl$ (aq) followed by appropriate aqueous workup, yielding the major organic product $\mathbf{Z}$ .

Which of the following correctly represents the rate of consumption of LTBA ( $-\frac{d[\mathbf{R}]}{dt}$ ) during the reduction, and the correct IUPAC name of product $\mathbf{Z}$ ?

Options

A.
$-\frac{d[\mathbf{R}]}{dt} = 2k[\mathbf{X}][\mathbf{R}]$ ; $\mathbf{Z}$ = 4-aminobenzene-1,2-dicarboxylic acid
B.
$-\frac{d[\mathbf{R}]}{dt} = k[\mathbf{X}][\mathbf{R}]^2$ ; $\mathbf{Z}$ = 4-aminobenzene-1,2-dicarboxylic acid
C.
$-\frac{d[\mathbf{R}]}{dt} = k[\mathbf{X}][\mathbf{R}]$ ; $\mathbf{Z}$ = 4-aminobenzene-1,2-dicarbaldehyde
D.
$-\frac{d[\mathbf{R}]}{dt} = 2k[\mathbf{X}][\mathbf{R}]$ ; $\mathbf{Z}$ = 4-aminobenzene-1,2-dicarbonyl dichloride

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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

Stoichiometric Coefficient Division|Reduction Selectivity (Sn/HCl vs LiAlH4)

Why This Question Is Tricky

Common Mistakes

This problem tests the intersection of chemical kinetics and reaction stoichiometry, specifically targeting the 'Stoichiometric Coefficient Division' trap.

Students often erroneously write the rate law based on the overall stoichiometry (e.g., Rate = $k[\mathbf{X}][\mathbf{R}]^2$ ) or fail to multiply the RDS rate by the stoichiometric requirement of the subsequent fast steps, leading to $-\frac{d[\mathbf{R}]}{dt} = k[\mathbf{X}][\mathbf{R}]$ .

Furthermore, it tests reagent selectivity and condition awareness: while $Sn/HCl$ reduces the nitro group, the hidden trap is the inevitable aqueous hydrolysis of the acid chloride groups, preventing the survival of the $-COCl$ groups or the formation of an aldehyde.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Chemical Kinetics - Class 12
Concept	Stoichiometric Coefficient Division
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free