Kinetic and Thermodynamic Stability of Intermediate Complexes in the Reactions of Oxidation of Some Heterocyclic Compounds with Cerium(IV)

Resumo

The kinetic and thermodynamic characteristics of intermediate cerium(IV) complexes with 8-oxyquinoline, 7-iodo-8-hydroxy-quinoline-5-sulfonic acid, and 1-phenyl-2,3-dimethyl-4-dimethylaminopyrazolone-5, which are formed at the first stage of oxidation of these heterocyclic compounds with cerium(IV), are studied by spectrophotometry, photometry, and pH-metry at ionic strength I = 2 in sulfuric acid solutions (pH 0.5–3.0) at 285.15–297.15 K. The composition of the complexes and the form in which the organic ligand is present in them are determined. The stability constants and rate constants of their intramolecular redox decomposition are identified. The general equation of the rate of redox process observed in the systems is obtained and the respective reaction model is proposed. The type of linear correlations between the thermodynamic and kinetic stability of intermediate complexes discussed in this study can be used in coordination chemistry for quantitative description of the reactions of oxidation of organic compounds with transition metal ions.