Conversion of Phenylmethyl ketone to Ethylbenzene

Introduction:
Phenylmethyl ketone, also known as acetophenone, can be converted into ethylbenzene through a one-step reaction using specific reagents. This conversion involves reducing the carbonyl group of the ketone to an alcohol and then further reducing it to a hydrocarbon.

Reagents:
The correct reagent for this one-step conversion is option 'B', which is Zn-Hg/HCl.

Explanation:
The Zn-Hg/HCl reagent is commonly referred to as Clemmensen reduction. It is a powerful reducing agent that is capable of converting carbonyl groups (such as ketones) into hydrocarbons.

Reaction mechanism:
The conversion of phenylmethyl ketone to ethylbenzene using Zn-Hg/HCl reagent can be explained through the following reaction mechanism:

1. Deprotonation:
The Zn-Hg/HCl reagent serves as a source of H- ions. In the presence of acidic conditions (HCl), the H- ions are generated, which can abstract a proton from the ketone.

2. Formation of carbanion:
The deprotonation of the ketone leads to the formation of a carbanion intermediate. This carbanion is stabilized by resonance with the aromatic ring.

3. Addition of Zn-Hg:
The carbanion intermediate then adds to the Zn-Hg, forming a new carbon-carbon bond. This step results in the formation of an alkyl zinc intermediate.

4. Acidic workup:
The alkyl zinc intermediate is then treated with an acidic workup, which involves the addition of HCl. This acidic environment helps in the removal of the zinc atom and the formation of the desired product, ethylbenzene.

Overall reaction:
The overall reaction can be summarized as follows:
Phenylmethyl ketone + Zn-Hg/HCl → Ethylbenzene

Conclusion:
In conclusion, the conversion of phenylmethyl ketone to ethylbenzene can be achieved in one step using Zn-Hg/HCl reagent. This reagent acts as a powerful reducing agent, allowing for the transformation of the carbonyl group into a hydrocarbon.