L. Hegedus et al., Chemical mechanism of the radical feedback loop in the classical BZ reaction. Malonyl bromite and oxalic acid as flow-through intermediates, PHYS CHEM P, 2(18), 2000, pp. 4023-4028
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).