Final answer:
Benzylic halogenation occurs when a hydrogen atom on a benzene ring is replaced by a halogen in the presence of a halogen and an iron catalyst, resulting in an aryl halide.
Step-by-step explanation:
Benzylic halogenation takes place under conditions where a hydrogen attached to a carbon atom that is in turn attached to an aromatic ring, like benzene, is replaced by a halogen atom. This type of reaction falls under the category of electrophilic aromatic substitution reactions. The benzene molecule is fairly stable and unreactive due to the electron delocalization within the six-membered ring structure. However, in the presence of a halogen and an iron catalyst, typically ferric chloride (FeCl3), the substitution reaction can occur, replacing one of the hydrogen atoms with a halogen atom to form an aryl halide.
In the typical reaction, halogenation of benzene leads to the substitution of a hydrogen atom with a halogen atom. This process requires a halogen like chlorine or bromine and an iron halide catalyst. The resulting aryl halide is a derivative of benzene where a halogen is directly attached to the aromatic ring, such as chlorobenzene or bromobenzene.