Chemical mechanism of the radical feedback loop in the classical BZ reaction. Malonyl bromite and oxalic acid as flow-through intermediates

High-pressure liquid chromatography (HPLC) and measurements of the CO2 prod uced were performed in the induction period of the classical Belousov-Zhabo tinsky (BZ) reaction (malonic acid-bromate-cerium catalyst in sulfuric acid medium). It was found that oxalic acid is a flow-through intermediate of t he reaction. This was confirmed with an independent qualitative test with t hiobarbituric acid. The concentration of oxalic acid grows in the induction period together with that of bromomalonic acid and dibromomalonic acid int ermediates. It is known that there are two negative feedback loops in the B Z reaction: one is via bromide and the other via organic free radicals. Oxa lic acid and also CO2 are products of this second loop where organic radica ls react with BrO2 radicals. The induction period was chosen for the presen t experimental studies because the above radical-radical reactions are most intense during that time. Based on the experimental results mechanistic pr oposals are made for the radical feedback loop. A method to accumulate mult ivalent organic acids present in very low concentrations in the BZ reaction was also developed. Applying this and a thermal decomposition method ethen etetracarboxylic acid (EETA) was identified as an oxidation product of etha netetracarboxylic acid (ETA).