When toluene is reacted with in the presence of anhydrous in the dark, what type of halogen replacem — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Toluene contains both an aliphatic part (the methyl group) and an aromatic part (the benzene ring). Reaction with $Cl_2$ in the presence of a Lewis acid catalyst like $FeCl_3$ (and absence of UV light) strongly favors heterolytic bond cleavage, generating the chloronium ion electrophile ($Cl^+$). The electron-rich aromatic ring undergoes electrophilic aromatic substitution. Because the methyl group is activating and ortho/para directing via hyperconjugation and inductive effects, the halogens replace hydrogens on the aromatic ring primarily at the ortho and para positions. This is classified as an aromatic halogen replacement. (Note: If the reaction were carried out under UV light or high heat without $FeCl_3$, it would undergo a free-radical mechanism resulting in aliphatic benzylic substitution).