Alternative Reaction Channels and Carbene Intermediates in the Ce⁴⁺-Malonic Acid and Ce⁴⁺-Bromomalonic Acid...

The Ce⁴⁺-malonic/bromomalonic acid reactions play an important role in the oscillatory Belousov-Zhabotinsky reaction. In this work CO₂ evolution from these reactions was studied with a sensitive and quantitative method, by converting the CO₂ to methane and measuring it with a flame ionization detector. It was found that the stoichiometries depend on the initial conditions in batch experiments or on the mixing rate of reagents in a semibatch reactor. These findings are explained by two main reaction channels:  one for recombination and another for decarboxylation. Decarboxylation itself has two separate routes, one is dominant at low while the other at high Ce⁴⁺ concentrations. In the latter, formation of more than two CO₂ molecules from one malonic/bromomalonic acid molecule was observed. Novel reaction schemes containing carbenes are proposed for these "high Ce⁴⁺" decarboxylation channels. To check the new mechanism, HPLC measurements are planned as a continuation of the research.