Evidence of malonyl radical controlled oscillations in the Belousov-Zhabotinskii reaction (malonic acid-bromate-cerium system)

Contribution of Malonyl Radical Control in the Classical Belousov-Zhabotinsky Reaction

“…There is evidence for this reaction because Br0 2 can be identified as an intermediate in strongly acidic bromate solutions [9]. By increasing the concentration of sulfuric acid from 1 M to 10 M a very high concentration of BrOj (about 9 x 10" 5 M) can be obtained ( Figure 5).…”

“…The experimental setup and the evaluation of the data are the same as described earlier [4,9,10]. For the potential measurements a homemade molten AgBr electrode [13] was used, which turned out to be not sensitive to Ce 4 + , contrary to commercially available electrodes.…”

“…Additionally, a jump of the electrode potential occurs towards a higher potential, apparently due to the formation of HOBr after the start of the autocatalytic oxidation of Ce 3+ by bromate. Using the same argument as discussed in [9], it can be derived from the behaviour of the electrode that the inhibition of the autocatalytic reaction is not due to the formation of bromide. Moreover, it is unreasonable to believe that bromide can be formed during the very short time period between the addition of Ce 4+ and the observed jump of the Ce 4+ concentration.…”

“…From this point of view it seems reasonable to include malonyl radicals as possible control intermediates in the BZ reaction. Indeed, oscillations can be observed in some BZ systems with a high malonic acid/bromate ratio and 3 M sulfuric acid as a reaction medium, which are apparently controlled by malonyl radicals [9]. Moreover, by the addition of chloride into BZ systems in 1 M sulfuric acid, oscillations without any induction period can be induced; in this case a synergetic process involving both chloride ions and malonyl radicals is assumed to be responsible for the onset of oscillations [10].…”

“…Moreover, by the addition of chloride into BZ systems in 1 M sulfuric acid, oscillations without any induction period can be induced; in this case a synergetic process involving both chloride ions and malonyl radicals is assumed to be responsible for the onset of oscillations [10]. A model based on radical control ("Radicalator") accounts for the observed phenomena [9], [10], It is well known [11,12] that one single oscillation occurs in some BZ systems (1 M sulfuric acid medium, starting the reaction by addition of Ce 4 + ) immediately after mixing the compounds. Oxygen can be considered as a scavenger of malonyl radicals, and in fact the single oscillation does not appear in solutions permanently saturated with pure oxygen.…”