ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Kinetics and mechanism of oxidation of 2,4-pentanedione by manganese(III) ions

M. Mrákavová and Ľ. Treindl

Department of Physical Chemistry, Faculty of Natural Sciences, Komenský University, 842 15Bratislava

Abstract:  The oxidation of 2,4-pentanedione by the Mn(III) ions in the solution of sulfuric acid is an inner-sphere reaction which proceeds via intermediary complexes. The reaction is a first-order reaction with respect to concentration of the Мп(III) ions even if the concentrations of both reactants are equal. The experimental rate constant k_exp/s^-1 increases initially linearly and subsequently nonlinearly with concentration of the substrate, reaches the maximum value and afterwards it decreases. A plausible reaction mechanism was proposed according to which the slow and rate-determining step is an intramolecular redox reaction of the intermediary Mn—Enol complex or of the less reactive Mn—(Enol)₂ complex. The temperature dependence of the experimental rate constant was used for evaluating the activation parameters, i.e. activation enthalpy and activation entropy which were also dependend on temperature. On the basis of tempera­ture dependence of these parameters, the activation heat capacities ΔC^≠_p =— 1.4 kJ mol^-1 K^-1 in the presence of oxygen and ΔC^≠_p= -2.2 kJ mol^-1 K^-1 in nitrogen atmosphere were calculated.

Full paper in Portable Document Format: 366a785.pdf

Chemical Papers 36 (6) 785–790 (1982)