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Question #44523

Difficulty: 8/10 | 🟢 Free

The Question

An open reactive distillation apparatus is charged with an equimolar liquid mixture of 2,2-dimethylpropanoic acid, 2-methylpropan-2-ol, and 1-butoxybutane. The mixture is heated to $80^\circ\text{C}$ in the presence of a catalytic amount of concentrated \ce{H2SO4}. Let $r_{est}$ be the rate of esterification, $r_{dehyd}$ be the rate of alcohol dehydration, and $r_{cleav}$ be the rate of ether cleavage. It is observed that the liquid-vapor equilibrium composition alters significantly over time due to the rapid evolution of a gas $\textbf{G}$ , violating the assumption of a static azeotrope. Which of the following represents the correct order of initial reaction rates and the identity of $\textbf{G}$ ?

Options

A.
$r_{est} > r_{dehyd} > r_{cleav}$ ; $\textbf{G} = \text{Water vapor}$
B.
$r_{dehyd} \gg r_{est} \approx r_{cleav}$ ; $\textbf{G} = \text{2-Methylprop-1-ene}$
C.
$r_{cleav} > r_{est} > r_{dehyd}$ ; $\textbf{G} = \text{But-1-ene}$
D.
$r_{est} \approx r_{dehyd} \approx r_{cleav}$ ; $\textbf{G} = \text{1-Butoxybutane vapor}$

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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

Azeotrope Boiling Point Logic|Esterification Steric Hindrance|Ether Cleavage Patterns

Why This Question Is Tricky

Common Mistakes

The question tests the student's ability to integrate chemical kinetics, steric effects, and phase equilibria.

The primary trap is the assumption that all acid-catalyzed reactions (esterification and ether cleavage) will proceed simply because the reagents are present and heated.

Students must recognize that severe steric hindrance (pivalic acid + tert-butanol) kinetically quenches esterification, and that ether cleavage of primary ethers requires a strong nucleophile, which \ce{H2SO4} lacks.

The 'hidden variable' is the $E1$ dehydration of the tertiary alcohol, which acts as a mass sink, selectively depleting one component and dynamically breaking the azeotropic phase equilibrium.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Solutions - Class 12
Concept	Azeotrope Boiling Point Logic
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free