CIE A Level Chemistry

Revision Notes

Syllabus Edition

First teaching 2020

Last exams 2024

|

7.3.1 Production of Halogenoarenes

Test Yourself

Production of Halogenoarenes

  • 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

Halogen Compounds - Formation of Chlorobenzene, downloadable AS & A Level Chemistry revision notes

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 2,4-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

Halogen Compounds - Formation of 2- and 4-Chloromethylbenzene, downloadable AS & A Level Chemistry revision notes

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

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

You've read 0 of your 0 free revision notes

Get unlimited access

to absolutely everything:

  • Downloadable PDFs
  • Unlimited Revision Notes
  • Topic Questions
  • Past Papers
  • Model Answers
  • Videos (Maths and Science)

Join the 80,663 Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Francesca

Author: Francesca

Fran studied for a BSc in Chemistry with Forensic Science, and since graduating taught A level Chemistry in the UK for over 11 years. She studied for an MBA in Senior Leadership, and has held a number of roles during her time in Education, including Head of Chemistry, Head of Science and most recently as an Assistant Headteacher. In this role, she used her passion for education to drive improvement and success for staff and students across a number of subjects in addition to Science, supporting them to achieve their full potential. Fran has co-written Science textbooks, delivered CPD for teachers, and worked as an examiner for a number of UK exam boards.