The Source of the Carbon Monoxide in the Classical Belousov-Zhabotinsky Reaction

Abstract

CO and CO2 evolution was measured in a cerium and in a ferroin-catalyzed Belousov−Zhabotinsky (BZ) reaction. These gases were stripped from the reaction mixture by a N2 carrier gas, mixed with H2, converted to methane on a Ni catalyst, and then measured by a flame ionization detector (FID). CO could be detected separately by absorbing CO2 on a soda lime column. In separate experiments it was proven that CO is produced in a reaction of BrO2• radicals with bromomalonic acid (BrMA). To this end BrO2• radicals were generated in two different ways:  (i) in the reaction HBrO2 + HBrO3 ↔ 2 BrO2• + H2O and (ii) by reducing HBrO3 to BrO2• by Fe2+. It was found that •OH radicals produced by Fenton's reagent can also generate CO from BrMA. We propose that CO can be formed when an inorganic radical (like BrO2• or •OH) reacts with the enol form of BrMA producing an acyl radical which decarbonylates in the next step. Malonic acid (MA)−BrMA mixtures were prepared by a new method modifying Zaikin and Zhabotinsky's original recipe to minimize the production of dibromomalonic acid (Br2MA).