Question

Identify the reagents to be used to complete the given reaction.

• A. \( \text{Br}_2 / \text{CCl}_4 \) \( B = \text{aq. KOH} \) \( C = \text{NaNH}_2 \) \( D = \text{Red hot Fe tube} \)
• B. \( \text{NaBr} \) \( B = \text{aq. KOH} \) \( C = \text{CaC}_2 \) \( D = \text{Red hot Ni tube} \)
• C. \( \text{CH}_3\text{Br} \) \( B = \text{aq. KOH} \) \( C = \text{Conc. HCl} \) \( D = \text{Red hot Pd tube} \)
• D. \( \text{Br}_2 / \text{CCl}_4 \) \( B = \text{aq. KOH} \) \( C = \text{Conc. H}_2\text{SO}_4 \) \( D = \text{Red hot Cu tube} \)

Hint:

In organic reactions, halogenation with \( \text{Br}_2/\text{CCl}_4 \), followed by elimination using sodium amide, and further reduction with a red-hot metal tube can lead to the formation of aromatic compounds like benzene.

Answer 1

The Correct Option is A

Step 1: Analyze the first step of the reaction.
The reaction starts with \( C_2H_5I \) (ethyl iodide), which undergoes nucleophilic substitution in the presence of an alkali (\( \text{aq. KOH} \)) to form ethene (\( C_2H_4 \)) and an alcohol (ethanol). This indicates that the reagent [A] is \( \text{Br}_2/\text{CCl}_4 \), which is used for halogenation and prepares the compound for the next step of reaction.

Step 2: Analyze the second step of the reaction.
In the second step, the reaction of ethene (\( C_2H_4 \)) with \( \text{NaNH}_2 \) (sodium amide) results in the formation of an alkyne. The alkyne then undergoes elimination in the presence of a red-hot metal tube (such as red-hot Fe) to form benzene (\( C_6H_6 \)).

Step 3: Confirm the reagents and conditions.
The reagents used are consistent with the Finkelstein reaction and elimination mechanisms:
- \( \text{Br}_2 / \text{CCl}_4 \) is used for halogenation.
- \( \text{aq. KOH} \) is used to prepare ethene.
- \( \text{NaNH}_2 \) is used to form the alkyne intermediate.
- \( \text{Red hot Fe tube} \) is used to complete the reaction and form the final product, benzene.

Step 4: Conclusion.
Thus, the correct reagents for the given reaction are as described in option (A). The correct answer is option (A).