The halogenation/chlorination of Toluene can occur in 2 methods of electrophilic substitution: The Chlorine either substitutes itself with a Hydrogen atom in the phenyl ring, or it substitutes with a Hydrogen atom in the Methyl group (side chain reaction) to form variants of Chloromethylbenzene/Benzyl Chloride (C6H5CH2Cl).
Electrophilic substitution/Chlorination into the ring
AlCl3 in dry ether/Fe to act as catalyst
Absence of UV light
Heat (around 50C)
Formation of 2-chloromethylbenzene through ring substitution of Toluene
Formation of 4-chloromethylbenzene through ring substitution of Toluene.
Photochemical free-radical substitution of Cl into the Methyl group:
Cl2 → 2Cl•
Cl2 gas undergoes homolytic fission in the presence of UV light to form 2 Chlorine radicals.
Hydrogen leaves Methyl group in Toluene to bond with a Chlorine radical to form Hydrochloric acid (HCl). Methyl group in Toluene is left radicalised (CH2•).
Additional Chlorine gas undergoes homolytic fission in the presence of UV light and bonds with the radicalised Toluene to form final product of Benzal Chloride (C7H7Cl).
2Cl• → Cl2
Excess Chlorine radicals bond together to reform Cl2 gas. Reaction is complete.
While hydrolysis of Benzal Chloride (C7H6Cl2) product will be Benzaldehyde.