Protonated carbonic acid and reactive intermediates in the acidic decarboxylation of indolecarboxylic acids

J Org Chem. 2012 Aug 3;77(15):6505-9. doi: 10.1021/jo301032f. Epub 2012 Jul 24.


Elucidation of the mechanism for decarboxylation of indolecarboxylic acids over a wide range of solution acidity reveals the importance of protonated carbonic acid (PCA) as a reaction intermediate. In concentrated acid, the initial addition of water to the carboxyl group of the indolecarboxylic acid leads to a hydrated species that is capable of releasing PCA upon rate-determining carbon-carbon bond cleavage. The overall process is catalytic in water and acid, implicating PCA as a potential carboxylating reagent in the microscopic reverse reaction.

MeSH terms

  • Carbonic Acid / chemistry*
  • Carboxylic Acids
  • Decarboxylation
  • Hydrogen-Ion Concentration
  • Indoles / chemistry*
  • Molecular Structure
  • Protons*


  • Carboxylic Acids
  • Indoles
  • Protons
  • indole-2-carboxylic acid
  • Carbonic Acid
  • indole-3-carboxylic acid