Catalytic Activity of Palladium(II) and Osmium(VIII) on the Oxidation of Chloramphenicol by Copper(III) Periodate Complex in Aqueous Alkaline Medium-A Comparative Kinetic and Mechanistic Approach

Chloramphenicol is considered a prototypical broad band spectrum antibiotic, alongside the tetracyclines, and finds extensive applications in pharmaceuticals. Hence, its oxidation kinetic study is of much significance in understanding the mechanistic profile in biological systems. In this regard, a systematic study of oxidation of chloramphenicol (CHP) by diperiodatocuprate(III) (DPC) in the presence of micro amounts (10(-8) mol/dm(3)) of Pd(II) and Os(VIII) catalysts has been investigated spectrophotometrically in aqueous alkaline medium at a constant ionic strength of 0.10 mol dm(-3). The reaction between CHP and DPC in alkaline medium exhibits 1:2 stoichiometry in both catalyzed reactions (CHP:DPC). The oxidation products in both reactions were found to be the same and were identified and confirmed by IR, GC-MS, and H-1 NMR. The order with respect to DPC concentration was unity, while the order with respect to CHP concentration varied from first order to zero order as the concentration of CHP increased. The rates increased with increase in [OH-] and decreased with increase in [IO4-]. The order with respect to [Pd(II)] and [Os(VIII)] was unity. It is observed that the catalytic efficiency for the title reaction is in the order of Pd(II) > Os(VIII). The catalytic constant was also determined at different temperatures for both reactions. The proposed mechanisms and the derived rate laws are in concurrence with the observed kinetics. The activation parameters with respect to the limiting step of the mechanism were calculated, and the thermodynamic quantities were also determined. Kinetic experiments suggest that [Cu(H2IO6)(H2O)(2)], [Pd(OH)(2)Cl-2](2-), and [OsO4(OH)(2)](2-) are the reactive oxidizing species of Cu(III), Pd(II), and Os(VIII).