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The kinetics of the reactions of the symmetric dimethyl-substituted-2,2′bipyridine with the ion of Ni(II) in methanol

1979; Pergamon Press; Volume: 41; Issue: 6 Linguagem: Inglês

10.1016/0022-1902(79)80276-6

1878-1225

Dagoberto Pacheco A., Ricardo H. Romero, J. D. Medina, V. De Santis, J. L. CALDERON,

Advanced NMR Techniques and Applications

The kinetics of formation of the complexes of the symmetric dimethyl-substituted-2,2′bipyridines with the Ni(II) ion in methanol were studied by the stopped-flow spectrophotometric method under pseudo-first order conditions ([Ni(II)] ⪢ [Lig]). Reaction-rates were measured at different temperatures and the activation parameters were calculated. The stability constants of the complexes were estimated by spectrophotometric method at 25.0°C. The results show that for ligands 4,4′-, 5,5′- and 6,6′-dimethyl-2,2′bipyridine the order of the reactions are composite of first-order with respect to the ligand concentration and first-order with respect to the nickel ion concentration, while for ligand 3,3′-dimethyl-2,2′bipyridine it was found to be first order with respect to the ligand concentration and to the square root of the nickel ion concentration. The second-order rate constant of the reaction of 6,6′-dimethyl-2,2′bipyridine is smaller than those 4,4′- and 5,5′-dimethyl-2,2′-bipyridines. Direct comparison of the rate of reaction of the 3,3′-dimethyl-2,2′bipyridine with the others is not possible due to the fact that the back-side crowding effect of the methyl groups does not allow the formation of the 1:1 complex.