RESUMO
Co(II) complexes and Co(H2O)6(2+) are used as catalysts in advanced oxidation processes. Therefore it was decided to study the kinetics of reaction of Co(H2O)6(2+) with H2O2. Surprisingly, the kinetic results point out that the process involves three consecutive reactions, each of them requiring an H2O2 molecule, i.e. three H2O2 molecules ligate to the central cobalt cation prior to the formation of radicals. DFT analysis suggests that the transient (H2O)3Co(II)(OOH)2(H2O2) decomposes via: (H2O)3Co(II)(OOH)2(H2O2) â (H2O)3Co(II)(OOH)(ËOOH)(OH) + ËOH ΔG(0) = -5.975 kcal mol(-1), with no evidence for the formation of a Co(III) transient. It is proposed that analogous mechanisms are involved whenever the redox potential of the central cation is too high to enable the reaction: M(H2O)6(n+) + H2O2 â M((n+1)+)aq + ËOH + OH(-).
Assuntos
Química/métodos , Cobalto/química , Peróxido de Hidrogênio/química , Ferro/química , Soluções Tampão , Cátions , Elétrons , Concentração de Íons de Hidrogênio , Iodetos/química , Ligantes , Metais/química , Distribuição Normal , Oxirredução , Oxigênio/química , Peróxidos/química , Software , Espectrometria de Massas por Ionização por Electrospray , Temperatura , TermodinâmicaRESUMO
Kinetic and DFT results for the carbonate catalysed Co(H2O)6(2+) + H2O2 Fenton-like reaction suggest a mechanism involving the formation of a cyclic transient, cyclic-(CO4)Co(II)(OOH)(H2O)2(-) that decomposes into Co(II)(H2O)(OOH)(OH)2 + CO3Ë(-), i.e. no OHË radicals are involved. Plausible biological implications are pointed out.