5.2.5 Kolbe- Schmidt Carboxylation
Phenoxide ions react with CO2(weak electrophile) under pressure at about 100°C to give ortho substitution.
Mechanism
The formation of ortho product predominates which may be due to the stabilizing influence of chelation on the transition state A .
Examples:
However, the Kolbe-Schmidt carboxylation is reversible at about 240°C and the formation of more stable para- isomer predominates.
The reaction conditions are also compatible with heterocyclic compounds. For example, pyrrole undergoes reactions at 120°C to give pyrrole-2-carboxylic acid.