Investigation of the Halogenate–Hydrogen Peroxide Reactions Using the Electron Paramagnetic Resonance Spin Trapping Technique

Abstract

The differences in the mechanism of the halogenate reactions with the same oxidizing/reducing agent, such as H 2 O 2 contribute to the better understanding of versatile halogen chemistry. The reaction between iodate, bromate, and chlorate with hydrogen peroxide in acidic medium at 60 °C is investigated by using the electron paramagnetic resonance (EPR) spin trapping technique. Essential differences in the chemistry of iodate, bromate, and chlorate in their reactions with hydrogen peroxide have been evidenced by finding different radicals as governing intermediates. The reaction between KIO 3 and H 2 O 2 is supposed to be the source of IO 2• radicals. The KBrO 3 and H 2 O 2 reaction did not produce any EPR signal, whereas the KClO 3 −H 2 O 2 system was found to be a source of HO • radical. Moreover, KClO 3 dissolved in sulfuric acid without hydrogen peroxide produced HO • radical as well. The minimal-core models explaining the origin of obtained EPR signals are proposed. Current findings suggested the inclusion of IO 2• and HOO • radicals, and ClO 2• and HO • radicals in the particular kinetic models of iodate−hydrogen peroxide and chlorate−hydrogen peroxide systems, as well as possible exclusion of BrO 2• radical from the kinetic scheme of the bromate−hydrogen peroxide system. Obtained results may pave the way for understanding more complex, nonlinear reactions of these halogen-containing species.

Transition from Low to High Iodide and Iodine Concentration States in the Briggs–Rauscher Reaction: Evidence on Crazy Clock Behavior

“…30,32 Consequently, thermodynamical considerations for reaction (eq 14), E 0 r (HOO • /H 2 O 2 ) = 1.436 V, 30 suggest a favorable process and an additional production of HOO • . The hydroperoxyl radical HOO • formed is known to be a good reducing agent (E 0 r (O 2 /HOO • ) = −0.186 V), 30,33 and it can effectively reduce iodomalonic and diiodomalonic acid to appropriate organic radical species, and further, produces chain carriers for radicals. Thus, eqs 13 and 14 underline the important role of metal catalyst and hydrogenperoxide in the later stage of BR reaction, when the strong oxidizing agent KIO 3 is completely consumed, and the oxidation product of malonic acid (iodomalonic acid and diiodomalonic acid) is formed.…”

Oscillatory reaction as a system detector for doped and undoped phosphate tungsten bronzes

“…Smatra se da se reakcije koje inhibitorno utiču na oscilatornu dinamiku, uglavnom odigravaju sa prisutnim HOO• radikalima generisanim u BR reakciji. Ovo, naravno, treba uzeti sa rezervom jer je BR reakcija potencijalni generator i drugih radikalskih vrsta (IO2•, I•, HO•, MAH•, IMA•, poslednja dva su radikali nastali iz malonske kiseline (MA) i jodomalonske kiseline (IMA)), ali i neradikalskih vrsta kao što su HIO2, HIO, I2, I - [33][34][35][36][37][38]. Izazvane promene u oscilatornoj dinamici dodatkom aktivnog analita/aditiva, se uspešno koriste za određivanje koncentracije aktivnog analita, ali i njegove potencijalne antioksidativne/antiradikalske aktivnosti [30].…”

Spontaneous Symmetry Breaking: The Case of Crazy Clock and Beyond

“…Substitutions of chemicals are possible; different acids, organic substrates, and ions, such as Ce(III) instead of Mn(II) catalyst, can be used to generate BR oscillations [7][8][9][10]. However, the oscillatory behavior is not the only one that attracted the attention of non-linear scientists in the Briggs-Rauscher reaction [11][12][13][14][15].…”