Structural reactivity relationship and thermokinetic investigation of oxidation of substituted anilines by iridium (IV) in solution media

The oxidation of para- and ortho-substituted anilines with iridium (IV) in aqueous perchloric acid has been investigated. The kinetic study reveals a first-order dependence with respect to both the oxidant and the substrates. The reaction rate increases with the presence of electron-donating groups and decreases with electron-withdrawing groups, which is explained by the linear free energy relationship (LFER) theory according to Hammett's equation. The Hammett reaction constant (ρ) is found to be negative (ρ < 0), and it increases with temperature. Various thermodynamic parameters have been evaluated, and the validity of the isokinetic relationship has been discussed. The isokinetic temperature (β), calculated from the Van't Hoff plot (317 K), Compensation plot (317.4 K), and Arrhenius plot (317 K), is consistent. However, the isokinetic temperature obtained from the Exner plot (439.32 K) exceeds the experimental temperature range (303-323 K), indicating that enthalpy factors likely play a more significant role in controlling the reaction. Based on the kinetic results, a probable reaction mechanism is proposed.