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

Abstract

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 1 H 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 [IO 4 − ]. 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(H 2 IO 6 )(H 2 O) 2 ], [Pd(OH) 2 Cl 2 ] 2− , and [OsO 4 (OH) 2 ] 2− are the reactive oxidizing species of Cu(III), Pd(II), and Os(VIII).

Reaction mechanism of chloramphenicol with hydroxyl radicals for advanced oxidation processes using DFT calculations

“…10 Free energy profiles for the oxidation of CAP by •OH in path B length between the cleavage bonds is longer than the length of the transition states between the transfer atoms in the hydrogen abstraction reactions, and the energy barriers during the bond-breaking process are so small that they seem no obstacle encountered during these processes. This result is in agreement with the experimental conclusion that the C-C bond in a free radical undergoes fast radical reaction to form one intermediate product and another free radical [41].…”

A DFT Mechanistic Study of the trans-[OsVIO2(OH)4]2– and [OsVIIIO4(OH)n]n− (n = 1, 2 cis) Comproportionation Proton-Coupled Electron Transfer Reaction

“…This will, among others, tie together our previously reported experimental and computational results concerning eq . − In doing so, we aim to (i) determine the most likely and most favorable PCET reaction pathway, (ii) uncover the reason(s) for the experimentally observed negative Δ ‡ H dis , and (iii) validate our DFT-calculated results and interpretations thereof by comparing with experimental data. These lines of enquiry expand current understanding of inorganic PCET reactions from a theoretical point of view, and considering that Os VIII species are widely used as a redox catalyst, eq must be taken into consideration when interpreting results. − …”

A DFT study to unravel the ligand exchange kinetics and thermodynamics of OsVIIIoxo/hydroxido/aqua complexes in aqueous matrices

“…There is extensive literature dealing with the use of Os VIII O 4 as a homogeneous catalyst for the oxidation of several organic compounds in a variety of acidic and basic aqueous solutions. [1][2][3][4][5][6][7][8] However, when Os VIII O 4 is extracted from CCl 4 into an aqueous hydroxide solution several possible Os VIII oxo/ hydroxido/aqua complexes can form. [1][2][3][9][10][11][12] To date, only the Os VIII O 4 13 and the cis-[Os VIII O 4 (OH) 2 ] 2− species [14][15][16] have been experimentally characterised, by means of X-ray diffraction spectrometry.…”