31 Halogen Compounds

31.1 Halogen Compounds:

1. Production of Halogenoarenes:
   1. Halogenoarenes are produced through the substitution reaction of an arene (such as benzene) with chlorine (Cl₂) or bromine (Br₂) in the presence of a Lewis acid catalyst, such as aluminum chloride (AlCl₃) or aluminum bromide (AlBr₃).
   2. The reaction is typically conducted under reflux conditions to ensure efficient substitution.
   3. Examples include the production of chlorobenzene from benzene and 2-chloromethylbenzene and 4-chloromethylbenzene from methylbenzene (toluene).
2. Reactivity of Halogenoalkanes vs. Halogenoarenes:
   1. Halogenoalkanes (alkyl halides) and halogenoarenes (aryl halides) exhibit different reactivities due to the nature of their molecular structures.
   2. Halogenoalkanes contain a halogen atom directly bonded to an alkyl group (-R), while halogenoarenes contain a halogen atom directly bonded to an aromatic ring.
   3. Halogenoalkanes are more reactive than halogenoarenes due to the presence of more easily polarizable carbon-halogen bonds, allowing for easier nucleophilic substitution reactions.
   4. In contrast, halogenoarenes are less reactive because the aromatic ring exhibits electron delocalization and provides stability to the molecule, making it less susceptible to nucleophilic attack.