Question

Which of the following reaction is not feasible?

• A.

  

• B.

  

• C.

  

• D.

  

Hint:

For dehydration reactions of alcohols, concentrated sulfuric acid and high temperatures are typically required for the reaction to proceed efficiently. Lower concentrations and temperatures may not favor the elimination reaction.

Answer 1

The Correct Option is B

The reaction involves the dehydration of ethanol to ethene, which is an example of an elimination reaction. The dehydration of alcohols occurs by the following mechanism: - For option (1), the reaction proceeds with concentrated \( \text{H}_2 \text{SO}_4 \) at 443 K, which is a feasible condition for dehydration of ethanol to form ethene. - For option (3), dehydration also occurs in the presence of 85% \( \text{H}_2 \text{SO}_4 \) at 440 K, which is again a feasible reaction. - For option (4), the reaction takes place with 20% \( \text{H}_3 \text{PO}_4 \) at 358 K, which is also feasible under the given conditions. - For option (2), the reaction occurs with 75% \( \text{H}_2 \text{SO}_4 \) at 300 K. However, at this relatively low temperature, the dehydration of ethanol to ethene is not favored, making this reaction non-feasible. Thus, the correct answer is option (2).

Answer 2

To determine feasibility, let's analyze the dehydration reaction shown in the image.

The reaction involves:
CH₃–CH₂–CH₂–CH₂–OH (butan-1-ol)
with 75% H₂SO₄ at 300 K (approx. 27°C), producing:
CH₃–CH₂–CH=CH₂ (but-1-ene)

Dehydration of alcohols to alkenes using H₂SO₄ typically requires around 443 K (170°C).
But here, the temperature is only 300 K, which is not sufficient for effective dehydration to take place.

Hence, this reaction is not feasible under the given conditions.

Correct Answer: The dehydration of butan-1-ol to but-1-ene at 300 K is not feasible.