Electrophilic aromatic halogenation
A halogen replaces a hydrogen on an aromatic ring, releasing the hydrogen halide.
What it needs, and what it gives
- Reaction class
- Electrophilic aromatic substitution
- A Lewis acid carrier such as FeCl3 or FeBr3; the halogen alone is not electrophilic enough for benzene. Where the ring already carries a group, that group decides which positions react.
- balanced — the co-products are written out, not dropped
- Mechanism
- Electrophilic aromatic substitution, 2 steps
- Elemental halogens are corrosive and toxic by inhalation.
These notes are flags, not a risk assessment. Read the primary source and your own institution's rules before working at the bench.
How it is thought to happen
The ring gives up its aromaticity for one step to attack the electrophile, then loses a proton to get it back.
- The ring attacks the electrophile
- A base takes the proton and the ring comes back
Try it on your own structures
Enter your reactants in the Reaction Lab. If this transformation matches what you drew, it is applied and the outcome is shown next to the records that back it — with the count of documented reactions doing the same thing on substrates like yours, rather than a confidence score.
Other electrophilic aromatic substitution transformations
Friedel-Crafts acylation
A Lewis acid pulls the halide off an acyl halide, and the aromatic ring attacks the acyl group. The groups already on the ring decide which carbon reacts.
Friedel-Crafts acylation with an anhydride
The same reaction with an anhydride as the acyl donor, releasing the carboxylic acid.