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Chapter 24: Phenols |  |
Acylation of Phenols
| Reaction type: | C-acylation = electrophilic aromatic substitution |
| O-acylation = nucleophilic acyl substitution |
- Phenols are examples of bidentate nucleophiles, meaning that they can react at two positions:
- on the aromatic ring giving an aryl ketone via C-acylation, a Friedel-Crafts reaction or,
- on the phenolic oxygen giving an ester via O-acylation, an esterification
- Reagents :
| C-acylation : acylating agent (acyl chloride or anhydride) and AlCl3 |
| O-acylation : acylating agent (acyl chloride or anhydride) |
- The product of C-acylation is more stable and predominates under conditions of thermodynamic control (i.e. when AlCl3 is present).
- The product of O-acylation forms faster and predominates under conditions of kinetic control
- O-acylation can be promoted by either:
- acid catalysis via protonation of the acylating agent, increasing its' electrophilicity or
- base catalysis via deprotonation of the phenol, increasing its' nucleophilicity.
- It is also known that aryl esters readily rearrange to aryl ketones in the presence of AlCl3, a reaction known as the Fries rearrangement:
Related reactions
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© Dr. Ian Hunt, Department of Chemistry |  |