BRAINCAKEHalogen Carriers
Benzene reacts with halogens only in the presence of a catalyst called a halogen carrier. The π-electrons in benzene are delocalised around the ring, so the electron density is too low to polarise a halogen molecule enough for it to attack. (An alkene's localised π-bond can do this, so alkenes react with bromine without a catalyst.)
Common halogen carriers are AlCl3, FeCl3, AlBr3 and FeBr3. Iron filings can also be used, because iron reacts with bromine to form FeBr3 in the reaction mixture. The reaction is carried out at room temperature under anhydrous conditions.
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Key terms in this lesson
- electrophilic substitution
- A reaction mechanism in which an electrophile is attracted to and attacks a region of high electron density, such as the delocalised ring in benzene, displacing a hydrogen atom.
- friedel-crafts reaction
- A halogen-carrier-catalysed reaction that forms a new carbon-carbon bond to a benzene ring, by alkylation or acylation.
More in Benzene
- Electrophilic Substitution Reactions
- Nitration of Benzene
- Halogenation of Benzene
- Phenol
- Friedel-Crafts Alkylation
- Friedel-Crafts Acylation
- Reactivity of Phenol
- Phenol as a Weak Acid
All 16 lessons in Benzene · All OCR A-level Organic Chemistry topics