Introduction
The reaction of toluene (C6H5CH3) with chlorine (Cl2) in the presence of iron(III) chloride (FeCl3) is an example of electrophilic aromatic substitution. This process typically leads to the chlorination of the aromatic ring of toluene.
Mechanism of Reaction
- The presence of FeCl3 acts as a Lewis acid, facilitating the generation of the electrophile, Cl+.
- The electrophilic attack occurs primarily on the aromatic ring of toluene, due to its electron-donating methyl group, which activates the ring towards electrophilic substitution.
Predominant Product
- The major product of this reaction is p-chlorotoluene.
Reasons for Predominance of p-Chlorotoluene
- Activating Effect of Methyl Group: The methyl group (–CH3) is an electron-donating group, which stabilizes the carbocation intermediate formed during the reaction.
- Ortho/Para Orientation: The methyl group directs new substituents predominantly to the ortho and para positions due to steric and electronic factors. However, steric hindrance at the ortho position makes the para position more favorable for substitution.
Minor Products
- Ortho-Chlorotoluene: Although some ortho substitution occurs, it is less favored due to steric hindrance.
- Dichlorinated Products: If excess Cl2 is present, further chlorination may lead to products like 2,4-dichlorotoluene.
Conclusion
In summary, the reaction of toluene with Cl2 in the presence of FeCl3 predominantly yields p-chlorotoluene, with the reaction mechanism favoring this product due to the directing effects of the methyl group on the aromatic ring.