OrganicAcids Tunably Catalyze Carbonic Acid Decomposition.

Density functional theory calculationspredict that the gas-phasedecomposition of carbonic acid, a high-energy, 1,3-hydrogen atom transferreaction, can be catalyzed by a monocarboxylic acid or a dicarboxylicacid, including carbonic acid itself. Carboxylic acids are found tobe more effective catalysts than water. Among the carboxylic acids,the monocarboxylic acids outperform the dicarboxylic ones whereinthe presence of an intramolecular hydrogen bond hampers the hydrogentransfer. Further, the calculations reveal a direct correlation betweenthe catalytic activity of a monocarboxylic acid and its pKa, in contrast to prior assumptions about carboxylic-acid-catalyzedhydrogen-transfer reactions. The catalytic efficacy of a dicarboxylicacid, on the other hand, is significantly affected by the strengthof an intramolecular hydrogen bond. Transition-state theory estimatesindicate that effective rate constants for the acid-catalyzed decompositionare four orders-of-magnitude larger than those for the water-catalyzedreaction. These results offer new insights into the determinants ofgeneral acid catalysis with potentially broad implications. [ABSTRACT FROM AUTHOR]