Which sequence of reaction conditions should be used to produce the compound below from benzene?
Correct answer: A. AlCl3 / Cl2 ; H2 / Rh / C
- A. AlCl3 / Cl2 ; H2 / Rh / C
- B. Cl2 / UV light ; H2 / Rh / C
- C. H2 / Rh / C ; AlCl3 / Cl2
- D. HCl ; H2 / Rh / C
Explanation
A would be the answer as we have electrophilic substitution taking place involving the formation of a Cl+ ion which is formed via the interaction of AlCl3 catalyst and Cl2 gas producing (AlCl4)- and Cl+. The Cl+ replaces Hydrogen from the benzene ring. Once chlorobenzene is formed, it is reduced by H2 gas and rhodium catalyst. Reducing the benzene ring first would form a cycloalkane and then, using AlCl3 + Cl2 would do nothing.
This question appeared on the NUMS 2018 paper, which you can sit online with every answer explained.
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About Benzene and Aromatic Compounds
Benzene has a planar ring of delocalised π electrons, giving aromatic stability and equal carbon-carbon bond lengths. The topic covers resonance, electrophilic substitution reactions such as nitration, halogenation, sulphonation and Friedel-Crafts reactions, along with substituent effects and the distinction between substitution in benzene and addition in ordinary alkenes.
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