A Comparative Kinetic, Mechanistic, and Computational Analysis of the Oxidation of Cinnamyl Alcohol by Thallium(III) in Aqueous Medium with or without Ruthenium(III) Catalyst

Extensive research has been conducted for the oxidation of cinnamyl alcohol by thallium(III) in aqueous acidic medium with or without ruthenium(III) catalyst through an integrated kinetic, mechanistic, and computational (DFT) approach to explore the effect of catalyst in the oxidation rate. Kinetic investigations indicate that, without a catalyst, the reaction exhibits a first-order dependence on both cinnamyl alcohol and thallium(III), as well as an inverse dependence on hydrogen ion concentration. This implies the participation of a neutral or deprotonated form of the alcohol, and the bimolecular interaction between TlOH2+ and cinnamyl alcohol constitutes the rate-limiting step. But in the presence of the ruthenium(III) catalyst, the system exhibits first-order dependency on both thallium(III) and the ruthenium(III) while demonstrating a variable order concerning cinnamyl alcohol, suggesting a dual-pathway mechanism that incorporates both catalyzed and uncatalyzed processes. The changing order in alcohol indicates the formation of a pre-equilibrium complex between the alcohol and the catalyst. The observed results signify the concurrent participation of all three species in the rate-determining phase. This exemplifies a ternary transition state, in which cinnamyl alcohol establishes a temporary coordination complex with Ru(III), thereafter interacting with thallium(III) to promote electron transfer. The activation parameters derived from Eyring plots for each reaction imply different mechanistic pathways. The catalyzed pathway exhibits increased reactivity and diminished activation barriers, whereas the uncatalyzed route proceeds at a slower rate. Density Functional Theory investigation signifies the existence of a termolecular transition state involving cinnamyl alcohol, thallium(III), and the ruthenium catalyst, accentuating the catalyst’s role as a redox mediator that expedites electron transfer. The novelty of the research lies in the detailed mechanistic understanding of thallium(III)-catalyzed cinnamyl alcohol oxidations in aqueous media with or without ruthenium(III) catalyst supported by the computational analysis and in describing the substantial impact of catalytic intervention on activation parameters and reaction pathways and providing essential insights for the development of effective catalytic oxidation systems.