Question

In the given sequence of reactions, identify ‘P’, ‘Q’ and ‘S’ respectively:

• A. Br₂, Alc, KOH, NaOH, Al₂O₃
• B. HBr, Alc, KOH, CaC₂, KMnO₄
• C. HBr, Alc, KOH, NaNH₂, Red hot iron tube
• D. Br₂, Alc, KOH, NaNH₂, Red hot iron tube

Hint:

The sequence transforms starting materials into benzene through bromination, elimination, and cyclization.

Answer 1

The Correct Option is D

Given the sequence of reactions, we need to identify the reagents 'P', 'Q', and 'S'. The reaction sequence is:

1. The first step involves converting an alkene to a dibromo compound. This reaction is typically performed using bromine in the presence of an inert solvent. Hence, P is \(\text{Br}_{2}, \text{Alc}\). 
2. The second step involves dehydrohalogenation to form a terminal alkyne. This requires a strong base. Thus, Q involves \(\text{KOH}\ (\text{alc})\), which is used for elimination to form an alkyne from a dibromo compound.
3. The alkyne reacts further to form the aromatic compound benzene. This step (S) generally requires a strong base followed by a red-hot iron tube for the conversion of alkynes to benzene; hence, S is \(\text{NaNH}_{2}\) and a red-hot iron tube.

Therefore, the correct sequence of reagents is: Br₂, Alc, KOH, NaNH₂, Red hot iron tube.

This matches with the correct answer choice provided: Br₂, Alc, KOH, NaNH₂, Red hot iron tube.