I(+1) transfer from diiodomalonic acid to malonic acid and a complete inhibition of the CO and CO2 evolution in the Briggs-Rauscher reaction by resorcinol

HOI versus HOIO selectivity of a molten-type AgI electrode

AgI electrode is often applied not only to determine iodine concentration but also to follow oscillations in the weakly acidic medium of the Bray-Liebhafsky and Briggs-Rauscher reactions where it partly follows the hypoiodous acid (HOI) concentration. It is known that HOI attacks its matrix in the corrosion reaction: AgI + HOI + H(+) ⇆ Ag(+) + I2 + H2O and the AgI electrode measures the silver ion concentration produced in that reaction. The signal of the electrode can be the basis of sensitive and selective HOI concentration measurements only supposing that an analogous corrosive reaction between AgI and iodous acid (HOIO) can be neglected. To prove that assumption, the authors calibrated a molten-type AgI electrode for I(-), Ag(+), HOI, and HOIO in 1 M sulfuric acid and measured the electrode potential in the disproportionation of HOIO, which is relatively slow in that medium. Measured and simulated electrode potential versus time diagrams showed good agreement, assuming that the electrode potential is determined by the HOI concentration exclusively and the contribution of HOIO is negligible. An independent and more direct experiment was also performed giving the same result. HOIO was produced with a new improved recipe.

CONCLUSION

an AgI electrode can be applied to measure the HOI concentration selectively above the so-called solubility limit potential.

Reactions of iodomalonic acid, diiodomalonic acid, and other organics in the Briggs-Rauscher oscillating system

It was found that oxalic acid is one of the main products in the Briggs-Rauscher oscillating reaction. In nonoscillating solutions, oxidation of iodomalonic acid and/or diiodomalonic acid by Fenton-type reactions also produced oxalic acid as well as I(2). Mesoxalic acid yielded oxalic acid under similar conditions. Tartronic acid was nearly inert to Fenton-type reactions; however, tartronic acid was oxidized by iodate and iodine to mesoxalic acid, which in turn could form oxalic acid in the presence of H(2)O(2) plus catalyst. Iodotartronic acid appeared to be a short-lived but significant intermediate, thus both tartronic acid and mesoxalic acid are possible intermediates. Glycolic acid and glyoxylic acid are not intermediates in the oxidation of iodomalonic acid, since they in turn produce formic acid under similar nonoscillating conditions.