Reaction Routes Leading to CO2 and CO in the Briggs−Rauscher Oscillator: Analogies between the Oscillatory BR and BZ Reactions

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• 作者：Norbert Muntean ; Gabriella Szab ; Maria Wittmann ; Thuy Lawson ; Jnos Flp ; Zoltn Noszticzius ; Lavinia Onel
• 刊名：Journal of Physical Chemistry A
• 出版年：2009
• 出版时间：August 13, 2009
• 年：2009
• 卷：113
• 期：32
• 页码：9102-9108
• 全文大小：176K
• 年卷期：v.113,no.32(August 13, 2009)
• ISSN：1520-5215

文摘

With Fenton-type experiments, it is shown that the intense CO₂/CO evolution in the Briggs−Rauscher (BR) reaction is due to decarboxylation/decarbonylation of organic free radicals. The metal ion applied in the Fenton-type experiments was Fe²⁺ or Ti³⁺ or Mn²⁺ combined with H₂O₂ or S₂O₈²⁻ as a peroxide, whereas the organic substrate was malonic acid (MA) or a 1:1 mixture of MA and iodomalonic acid (IMA). Experiments with a complete BR system applying MA or the MA/IMA mixture indicate that practically all CO₂ and CO comes from IMA. The decarboxylation/decarbonylation mechanisms of various iodomalonyl radicals can be analogous to that of the bromomalonyl radicals studied already in the Belousov−Zhabotinsky (BZ) reaction. It is found that an intense CO₂/CO evolution requires the simultaneous presence of H₂O₂, IO₃⁻, Mn²⁺, and IMA. It is suggested that the critical first step of this complex reaction takes place in the coordination sphere of Mn²⁺. That first step can initiate a chain reaction where organic and hydroperoxyl radicals are the chain carriers. A chain reaction was already found in a BZ oscillator as well. Therefore, the analogies between the BR and BZ oscillators are due to the fact that in both mechanisms, free radicals and, in most cases, also transition-metal complexes play an important role.