Kinetics of Decarboxylation of Ethylmalonic Adid:A Hundredfold Reactivity of the Acid Molecule over its Mono-anion

摘要

The kinetics of molten and aqueous ethylmalonic acid have been studied. The acid molecule us about 100 times more reactive than its carboxylate ion. while the dicarboxylate ion is unreactive. Increasing pH sharply impedes the reaction due to depletion of the concentration of the active species, viz,the unionized acid molecule. Investigation of solvent effect with water-dioxane system indicates that the reaction is most facile in media containing 75-85% dioxane.This has been explained based on the degree of dissociation of ethylmalonic acid and also on a kinetic solvent effect.The Arrhenius parameters for reactions in molten and aqueous solution have been evaluated. These data fall well in line with those on other malonic acids, and suggest a mechanism involving a concerted-switch of electrons in the intra-molecularly hydrogen-bonded molecule.