Benzene is treated with oleum to produce compound (X) which when further heated with molten sodium hydroxide followed by acidification produces compound (Y).The compound Y is treated with zinc metal to produce compound (Z). Identify the structure of compound (Z) from the following option.
Option corresponding to structure (1)
Option corresponding to structure (2)
Option corresponding to structure (3)
Option corresponding to structure (4)
Correct answer:B
Standard Method
Given: Benzene is treated with oleum to form compound (X). Compound (X) on heating with molten sodium hydroxide followed by acidification gives compound (Y). Compound (Y) is then treated with zinc metal to form compound (Z).
Find: The structure of compound (Z).
Benzene reacts with oleum to give benzene sulfonic acid, so (X) is benzene sulfonic acid.
On heating benzene sulfonic acid with molten sodium hydroxide followed by acidification, the sulfonic acid group is replaced by hydroxyl, giving phenol. Therefore (Y) is phenol.
Phenol on treatment with zinc dust is reduced to benzene.
Therefore, compound (Z) is benzene.
The correct option is B.
Using the Reaction Sequence
Follow the reaction sequence step by step:
Thus the final product is benzene, which matches option B.
There is a discrepancy in the provided second approach solution, which states phenol gives cyclohexanol. That statement is incorrect for this reaction sequence. The first solution and the stated correct option B are consistent with the correct chemistry.
Assuming oleum adds an group directly to benzene. This is wrong because oleum causes sulfonation, forming benzene sulfonic acid first. Track the functional group introduced in each step carefully.
Thinking molten sodium hydroxide leaves the sulfonic acid group unchanged. This is incorrect because alkaline fusion converts the sulfonic acid derivative into phenol after acidification. Use the standard conversion of aryl sulfonic acid to phenol.
Confusing the action of zinc dust on phenol with hydrogenation. Zinc dust removes oxygen from phenol to regenerate benzene; it does not form cyclohexanol. Distinguish reduction by zinc dust from catalytic hydrogenation.
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