Journal of the Brazilian Chemical Society
versión impresa ISSN 0103-5053
versión On-line ISSN 1678-4790
CARVALHO, Luciana B. et al. Autoxidation of Ni(II) and Co(II) tetra, penta and hexaglycine complexes accelerated by oxy sulfur radicals. J. Braz. Chem. Soc. [online]. 2006, vol.17, n.7, pp.1400-1408. ISSN 0103-5053. http://dx.doi.org/10.1590/S0103-50532006000700030.
The autoxidation of Ni(II) and Co(II) complexes with tetra, penta and hexaglycine, in borate medium, is accelerated by sulfur(IV) species (H2SO3, HSO3- and SO32-). The formation of Ni(III) and Co(III) complexes was followed spectrophotometrically at 325 and 265 nm, respectively. Electrochemical techniques were also employed to characterize the generation of these complexes. The autoxidation rate increases with S(IV) concentration and is maximum at pH @ 8.5. The process is autocatalytic with Ni(III) or Co(III) acting as initiators, formed by spontaneous oxidation by oxygen. The dependence of the pseudo first order rate constant with sulfite concentration showed evidences of back or parallel reactions with formation of mixed ligand complex prior to the oxidation step.
Palabras clave : nickel; cobalt; pentaglycine; hexaglycine; sulfite.