• Halogenoarenes?are arenes which are bonded to?halogen?atoms
• They can be prepared from?substitution reactions?of arenes with chlorine or bromine in the presence of an anhydrous catalyst

Substitution of benzene to form halogenoarenes

• Chlorine gas is bubbled into benzene at room temperature and in the presence of an anhydrous AlCl₃?catalyst to form?chlorobenzene
• The AlCl₃?catalyst is also called a?halogen carrier?and is required to generate the?electrophile?(Cl⁺)
• This electrophile?attacks?the electron-rich benzene ring in the?first stage?of the reaction which?disrupts?the delocalised π system in the ring
• To restore the?aromatic stabilization,?a hydrogen atom is removed in the?second stage?of the electrophilic substitution reaction to form chlorobenzene
• When this happens, the delocalised π system of the ring is?restored
• The same reaction occurs with benzene and bromine in the presence of an AlBr₃?catalyst to form?bromobenzene

Halogenoarenes can be formed from the electrophilic substitution reaction of arenes with halogens

Substitution of methylbenzene to form halogenoarenes

• The?electrophilic substitution?of?methylbenzene?with halogens results in the formation of multiple halogenoarenes as products
• This is because the methyl group (which is an?alkyl?group) in methylbenzene is?electron-donating?and pushes?electron density?into the benzene ring
• This makes the benzene ring?more?reactive?towards electrophilic substitution reactions
• The methly group is said to be 2,3-directing and as a result, the?2?and?4?positions?are?activated
• Electrophilic substitution of methylbenzene with chlorine and anhydrous AlCl₃?catalyst, therefore, gives?2-chloromethylbenzene?and?4-chloromethylbenzene
• The reaction mechanism is?the same?as the substitution mechanism of benzene

The methyl group on methylbenzene directs the incoming halogen on the 2 and 4 positio

• In the presence of?excess?chlorine, substitution on the?6 position?will also occur