Question

In the following reaction, condition 'A' is -

• A. Reduction with Zinc dust
• B. Dehydration with \(\text{H}_2\text{SO}_4\) / 443 K
• C. Treatment with \(\text{CS}_2\) / low temperture
• D. Oxidation with \(\text{CrO}_3\)

Hint:

Phenol is oxidised to p-benzoquinone by chromic acid.

Answer 1

The Correct Option is D

Step 1: Approach
Compare the starting material and the product atom by atom.

Step 2: Comparison
Start: one OH and five ring carbons with hydrogen. End: two C=O groups at the 1 and 4 positions, with two C=C bonds left in the ring. Oxygen has been added and hydrogen removed, which means oxidation.

Step 3: Reagent
A strong oxidising agent such as chromic acid (CrO$_3$) does this. Zinc dust is reducing, concentrated sulfuric acid at 443 K is a dehydrating condition, and carbon disulfide is a solvent for bromination.

Step 4: Conclusion
Condition A is oxidation with $\text{CrO}_3$, option (D).

Final Answer:
Phenol is oxidised by chromic acid to p-benzoquinone, option (D). \[ \boxed{\text{Oxidation with CrO}_3} \]