Identify ' $\mathrm{A}$ ' in the following reaction.
Identify ' $\mathrm{A}$ ' in the following reaction.
Benzene
Chlorobenzene
Toluene
Phenol
Solution
This is an example of a Friedel-Crafts Alkylation reaction. In this reaction:
- An alkyl group \(\left(-\mathrm{CH}_3\right)\) is introduced into an aromatic compound in the presence of a catalyst like anhydrous \(\mathrm{AlCl}_3\).
- The products are ortho- and para- substituted chlorotoluenes (2-Chlorotoluene and 4Chlorotoluene).
From the products (2-Chlorotoluene and 4-Chlorotoluene), it is evident that the starting compound A must already contain a chlorine atom on the benzene ring (a chlorobenzene).
Reaction:
\(\text {Chlorobenzene }+\mathrm{CH}_3 \mathrm{Cl} \xrightarrow{\mathrm{AlCl}_3} \text { 2-Chlorotoluene + 4-Chlorotoluene }\)
Mechanism:
1. The \(\mathrm{CH}_3^{+}\)(methyl cation) is generated by the action of \(\mathrm{CH}_3 \mathrm{Cl}\) and \(\mathrm{AlCl}_3\).
2. Electrophilic substitution occurs on chlorobenzene at the ortho and para positions due to the electron-donating resonance effect of the chlorine atom.
Correct Answer: (2) Chlorobenzene
