Estudos cineticos da reação dos derivados benzila da cobaloxima com Hg (C104)2

AUTOR(ES)

Nadia Regina Quilici

DATA DE PUBLICAÇÃO

1992

RESUMO

In this work, the kinetics of the reactions of benzyl derivatives of cobaloxime and Hg(ClO4)2 in aqueous HClO4 vere investigated. The kinetic measurements were made under pseudo-first order conditions, with Hg(ClO4)2 always in excess. The study included eleven complexes, with the temperature constant at 25,0°C. The concentrations of cobaloxime, of mercury(II) perchlorate and acid were varied, one at a time, fixing the others and maintaining the ionic strength constant. A study of the effect of the ionic strength was also made, fixing the concentrations and varying the ionic strength using perchlorate salts of lithium, sodium, barium, calcium and magnesium. The kinetics were determined using a spectrophotometer and analyzed using a microcomputer. From these data, one concludes that the reaction procedes in two steps. By varying the concentration of the cobaloxime, it was confirmed that the conditions used in this study are the pseudo-first order and that the order of the cobaloxime is one. The variation of the concentrations of Hg(ClO4)2 verified that the reaction is first order in Hg(II) and the second order rate constants were also determined in the specific conditions for this study. By varying the concentration of the acid, it was found that the two species of cobaloxime, protonated and non-protonated, present in the solution, react differently. For the first step, the protonated species generally reacts faster, while, for the second step, the non-protonated species reacts preferencially. By varying the ionic strength, it was observed that the rate of the reaction increases with an increase in the ionic strength. A specific ion charge effect for the first step also was evident. Finally, a mechanism for the reaction was proposed based on the obtained results. The mechanism can be treated as "two parallel consecutive reactions".

ASSUNTO(S)

bioquimica quimica bioinorganica

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