Kinetic modeling of mixed-acid nitration: From measurable rate constants to transferable parameters

Nitration in mixed acids, the ternary HNO 3 -H 2 SO 4 -H 2 O system, is among the most industrially important and hazardous reaction classes in organic chemistry, yet its kinetic behavior remains incompletely rationalized after more than a century of investigation. The central difficulty is not merely experimental: it is structural. In a strongly non-ideal medium where the concentration of the active electrophile, the nitronium ion (NO 2 + ), depends nonlinearly on acid composition, temperature, and water activity, any kinetic parameter measured under one set of conditions carries limited predictive value under another. This review examines the problem of kinetic modeling in mixed-acid nitration from a framework perspective, organizing the available approaches, i.e. empirical rate laws, activity-corrected mechanistic models, thermodynamic-kinetic coupled descriptions, computational pre-screening, and data-driven methods, according to their underlying assumptions, data requirements, and transferability. The Marziano acidity function ( M a ) and the related transformation of observed rate constants (k obs ) into intrinsic rate constants (k*) are identified as the most powerful currently available tools for obtaining kinetic parameters that are independent of acid composition and transferable across substrates and reactor configurations. The role of continuous flow microreactor technology as an enabling platform for reliable kinetic determination is critically assessed. Persistent gaps, including the absence of standardized protocols, the scarcity of validated thermodynamic models for ionic species, and the limited coverage of non-aromatic substrates, are identified, and directions toward a unified, multiscale kinetic framework for mixed-acid nitration are outlined.