Mechanistic Insights into m-T oluic Acid Nitration in Nitric Acid under Intrinsic Kinetic and Dissolution-Diffusion Controlled Regimes

3-Methyl-2-nitrobenzoic acid, a key intermediate in the synthesis of the broad-spectrum insecticide chlorantraniliprole, is predominantly produced via the nitration of m -toluic acid in a nitric acid medium. However, nitric acid is characterized by relatively low acidity, limited availability of the nitronium ion (NO 2 + ), and low solubility of m -toluic acid, leading to complex and poorly understood interactions between reaction kinetics and mass-transfer that significantly constrain industrial production and application. In this study, a unified kinetic framework was established that systematically integrated medium thermodynamics, intrinsic reaction kinetics, and mass-transfer behavior for m -toluic acid nitration in nitric acid. By incorporating acidity function and water activity, the intrinsic nitration kinetics were determined for the first time under rigorous conditions that eliminated mass-transfer limitations. The acidity function was calculated from dissolution enthalpy data using the van’t Hoff equation, while water activity was evaluated using the Pitzer model. Both dissolution and shrinking-core models were evaluated, with the dissolution model more accurately capturing the reaction behavior of large-flake particles. Furthermore, a reaction-diffusion coupling model was developed, and its predictions showed excellent agreement with experimental data. This work provides critical guidance for reactor design, process intensification and optimization, and the safe scale-up of m -toluic acid nitration in nitric acid.