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Carboxylation of Phenols (Kolbe-Schmitt reaction)

reaction of a phenolate with CO2

Reaction type: Electrophilic Aromatic Substitution


  • Heating the nucleophilic phenolate salt with carbon dioxide under high pressure / temperature results in regioselective ortho-substitution.
  • This process is also known as the Kolbe-Schmitt synthesis.
  • o-hydroxybenzoic acid is more commonly known as salicyclic acid.
hydrogen bonding in salicylate
Check out the CHIME image for the intramolecular hydrogen bond by looking the the postion of the shared H atom with respect to the two oxygen atoms


  • Aspirin is the acetyl ester of salicylic acid (hence ASA),  how would you make aspirin from salicylic acid ? ANSWER
  • Can you think of other reactions of nucleophilic species with carbon dioxide ? ANSWER
Study Tip:
Consider the phenolate to be an enolate, hence reactions at the a-C are typically favoured. 
Step 1:
The nucleophilic phenolate (reacting like an enolate) reacts with the electrophilic carbon of carbon dioxide in the ortho position (compare this with an Aldol reaction)
mechanism of the carboxylation of a phenolate
Step 2:
The non-aromatic cyclohexadienonecarboxylate intermediate tautomerises to the more stable aromatic enol which is further stabilised by an intramolecular hydrogen bond.  An acidic work-up will generate the carboxylic acid.

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organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary