Kinetic studies of the oxidation of L-ascorbic acid by tris(oxalate)cobaltate in the presence of CDTA metal ion complexes

It was investigated the kinetic of the reduction reaction of tris(oxalate)cobaltate by L-ascorbic acid, H2A, at different acidity. The Co(III) complex was monitored at 600 nm, under pseudo-first-order conditions: [H2A] = 3.0 x 10-2 mol L-1, [Co(C2O4)3]3- = 3.0 x 10-3 mol L-1, in the presence of CDTA (3.0 x 10-3 mol L-1) and ionic strength 1.0 mol L-1, (NaCl) at 25.0±0.1 ºC. The catalytic activity of CDTA metal ion complexes of Fe(III), Ni(II), Cu(II), Cr(III) and Mn(II) was also examined. The pseudo-first-order rate constant was proportional to the concentration of Fe(III)/CDTA, which is the best catalyst, in the range of (1-10) x 10-5 mol L-1.Realizaram-se estudos cinéticos envolvendo a reação de redução de tris(oxalato)cobaltato por L-ácido ascórbico, em diferentes valores de pH. A variação da concentração do complexo de Co(III) foi acompanhada pela absorbância em 600 nm, em condições de pseudo-primeira ordem: [H2A] = 3,0 x 10-2 mol L-1, [Co(C2O4)3]3- = 3,0 x 10-3 mol L-1, na presença de CDTA (3,0 x 10-3 mol L-1), em I = 1,0 mol L-1 (NaCl) e a 25,0±0,1 ºC. Foram investigadas as atividades catalíticas dos complexos de CDTA com Fe(III), Ni(II), Cu(II), Cr(III) e Mn(II). Para Fe(III)/CDTA, o melhor catalisador, os valores de constantes de velocidade observada de pseudo-primeira ordem foram proporcionais à concentração de ferro (1-10) x 10-5 mol L-1