Autoxidation of Ni(II) and Co(II) tetra, penta and hexaglycine complexes accelerated by oxy sulfur radicals

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 SO3(2-)). 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 <FONT FACE=Symbol>@</FONT> 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.

Bibliographic Details

Main Authors:	Carvalho,Luciana B., Alipázaga,María V., Lowinsohn,Denise, Bertotti,Mauro, Coichev,Nina
Format:	Digital revista
Language:	English
Published:	Sociedade Brasileira de Química 2006
Online Access:	http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532006000700030
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