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NEET CHEMISTRYMedium

Using anhydrous AlCl3\text{AlCl}_3 as a catalyst, which one of the following reactions produces ethylbenzene (PhEt)?

A

CH3-CH=CH2+C6H6\text{CH}_3\text{-CH=CH}_2 + \text{C}_6\text{H}_6

B

H2C=CH2+C6H6\text{H}_2\text{C=CH}_2 + \text{C}_6\text{H}_6

C

H3C-CH3+C6H6\text{H}_3\text{C-CH}_3 + \text{C}_6\text{H}_6

D

H3C-CH2OH+C6H6\text{H}_3\text{C-CH}_2\text{OH} + \text{C}_6\text{H}_6

Step-by-Step Solution

Ethylbenzene can be prepared by the Friedel-Crafts alkylation of benzene. While alkyl halides are typically used, alkenes can also serve as the alkylating agent in the presence of a Lewis acid catalyst such as anhydrous AlCl3\text{AlCl}_3 (often with a trace of HCl\text{HCl} to generate the initial electrophile). Thus, the reaction of benzene (C6H6\text{C}_6\text{H}_6) with ethene (H2C=CH2\text{H}_2\text{C=CH}_2) produces ethylbenzene.

  • Option A: Reaction with propene (CH3-CH=CH2\text{CH}_3\text{-CH=CH}_2) would yield isopropylbenzene (cumene) .
  • Option C: Alkanes like ethane (H3C-CH3\text{H}_3\text{C-CH}_3) do not undergo this reaction.
  • Option D: While alcohols can act as alkylating agents, they typically require a protic acid like H2SO4\text{H}_2\text{SO}_4, as the water byproduct would complex with and deactivate a Lewis acid like AlCl3\text{AlCl}_3.
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