Alternative reaction channels and carbene intermediates in the Ce4+-malonic acid and Ce4+-bromomalonic acid reactions. 1. CO2 measurements

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 acid quantitative method, by c onverting the CO2 to methane and measuring it with a flame ionization detec tor. It was found that the stoichiometries depend on the initial conditions in batch experiments or on the mixing rate of reagents in a semibatch reac tor. These findings are explained by two main reaction channels: one for re combination and another for decarboxylation. Decarboxylation itself has two separate routes, one is dominant at low while the other at high Ce4+ conce ntrations. In the latter, formation of more than two CO2 molecules from one malonic/bromomalonic acid molecule was observed. Novel reaction schemes co ntaining carbenes are proposed for these "high Ce4+" decarboxylation channe ls. To check the new mechanism, HPLC measurements are planned as a continua tion of the research.