Comparative kinetic analysis of oxidation reactions of Piperidone derivatives by Mn(III), Mn(IV), and Mn(VII) in acidic media

Transition metal ions, particularly manganese in its multiple oxidation states, play a pivotal role in redox chemistry due to their variable valencies and rich coordination behavior. Manganese-based oxidants such as Mn(III), Mn(IV), and Mn(VII) are extensively utilized in organic synthesis and environmental remediation. Their oxidation reactions, especially in acidic media, are of substantial importance for understanding fundamental mechanisms that govern electron transfer processes, complex formation, and reaction kinetics. This study presents a comprehensive comparative kinetic analysis of the oxidation of piperidone derivatives-specifically, 2,6-diphenylpiperidine-4-one and 3-methyl-2,6-diphenylpiperidine-4-one-by Mn(III), Mn(IV), and Mn(VII) ions in acidic environments. The reactions were conducted in sulphuric acid media with ionic strength maintained at 1.8 M using sodium sulphate, while kinetic measurements were carried out spectrophotometrically at different temperatures (25 °C to 55 °C). Pseudo-first-order conditions were established by maintaining a large excess of substrate over the oxidant. The reaction order with respect to each species was determined, and the effects of acidity, temperature, and substrate structure were examined. This research paper reveal that Mn(IV) exhibits the highest oxidizing power, followed by Mn(III) and Mn(VII). The oxidation rate was consistently higher for 2,6-diphenylpiperidine-4-one compared to its 3-methyl-substituted analogue, indicating that the presence of a methyl group at the 3-position reduces the reactivity due to increased steric hindrance and electronic effects. The activation parameters-enthalpy (?H*), entropy (?S*), and free energy (?G*)-were calculated, showing that the reactions are endothermic and proceed through well-defined transition states. Notably, the negative entropy values for some reactions imply a more ordered transition state, particularly in Mn(VII) systems. Solvent polarity and dielectric constant were found to significantly affect the rate constants, supporting the ionic nature of the reactants. Product analysis via GC-MS indicated the formation of either pyrrolidine-3-carboxylic acid or amino-dicarboxylic acid, with intermediate formation pathways proposed. This study provides mechanistic clarity and quantitative insight into how oxidation state, substrate structure, and solvent dynamics collectively influence reaction kinetics. The outcomes not only advance the theoretical understanding of manganese-based oxidation systems but also serve as a foundational reference for designing selective and efficient oxidation protocols in synthetic organic and industrial chemistry.