Final answer:
Ethylbenzene is prepared by acetylation of benzene followed by reduction to avoid polysubstitution, which is common when directly alkylating benzene due to the alkyl group activating the benzene ring.
Step-by-step explanation:
Ethylbenzene is typically prepared by the acetylation of benzene, followed by reduction rather than by the direct alkylation of benzene. This is predominantly due to control over the product distribution. When benzene is alkylated using an alkyl halide with a catalyst like aluminum chloride, there is a high possibility of obtaining polysubstituted products, such as diethylbenzene or even more substituted compounds, because the alkyl group is activating and directs further substitution to the ortho and para positions of the benzene ring.
However, by firstly acetylating benzene to form acetophenone and then reducing it to ethylbenzene, chemists can avoid the issues associated with polyalkylation and have better control over the stoichiometry and the final product. The reduction step typically uses a metal catalyst such as palladium on carbon (Pd/C) and hydrogen gas, which preferentially reduces the carbonyl group of the acetophenone to an ethyl group attached to the benzene ring, giving a high yield of ethylbenzene.
This method is more practical for industrial applications, even though it might seem more indirect than direct alkylation. It's like using a detour that's free of traffic to reliably get to your destination on time, rather than taking a more direct route that's often congested.