Alternative Reaction Channels and Carbene Intermediates in the Ce-Malonic Acid and Ce-Bromomalonic Acid Reactions. 1. CO Measurements.

The Ce-malonic/bromomalonic acid reactions play an important role in the oscillatory Belousov-Zhabotinsky reaction. In this work CO evolution from these reactions was studied with a sensitive and quantitative method, by converting the CO 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 Ce concentrations. In the latter, formation of more than two CO molecules from one malonic/bromomalonic acid molecule was observed. Novel reaction schemes containing carbenes are proposed for these "high Ce" decarboxylation channels. To check the new mechanism, HPLC measurements are planned as a continuation of the research.