Question

Identify 'Z' in the following series of reactions: \[ \text{Butan-2-ol} \xrightarrow{\text{PCl}_3} X \xrightarrow{\text{alc. KOH}} Y \xrightarrow{i) \, \text{H}_2\text{SO}_4, \, ii) \, \text{H}_2\text{O}/\text{heat}} Z \]

• A. Butan-1-ol
• B. 2-chlorobutane
• C. Butan-2-ol
• D. But-2-ene

Hint:

When alcohols react with PCl\(_3\), they form alkyl chlorides. Alcoholic KOH induces elimination to form alkenes.

Answer 1

The Correct Option is D

Step 1: Analyzing the Reaction Sequence.
In the given sequence, the reaction starts with butan-2-ol. - In the first step, when butan-2-ol reacts with phosphorus trichloride (PCl\(_3\)), it undergoes chlorination to form 2-chlorobutane (X). - In the second step, when 2-chlorobutane reacts with alcoholic potassium hydroxide (alc. KOH), it undergoes elimination to form But-2-ene (Y). - In the final step, when But-2-ene is treated with sulfuric acid (H\(_2\)SO\(_4\)) and then heated, it undergoes dehydration to form But-2-ene (Z). Hence, Z is But-2-ene.

Step 2: Analyzing the options.
(A) Butan-1-ol: Incorrect. Butan-1-ol is not formed in this reaction sequence.
(B) 2-chlorobutane: Incorrect. 2-chlorobutane is formed in the first step of the reaction but is not the final product.
(C) Butan-2-ol: Incorrect. Butan-2-ol is the starting material, not the final product.
(D) But-2-ene: Correct. But-2-ene is the final product after the elimination and dehydration steps.

Step 3: Conclusion.
The correct answer is But-2-ene, corresponding to option (D).