Density functional theory study on the reaction mechanism of 1-nitroanthraquinone synthesis by nitration of anthraquinone mixed acid

The nitration reaction of anthraquinone to produce 1-nitroanthraquinone is a key transformation process in industrial production. However, the reaction mechanism and product selectivity of this process remain unclear, which has long been a challenge in this field. This study employs density functional theory calculations combined with an implicit solvent model for the first time, fully revealing the atomic-level mechanism of this reaction under mixed acid conditions. By innovatively integrating kinetic and thermodynamic analyses, we conclusively established a classical two-step electrophilic aromatic substitution pathway. The rate-determining step was identified as the attack of the N-nitroso ion on the C1 position, forming the Wheland intermediate (energy barrier: 7.327 kcal/mol), followed by a kinetically favorable deprotonation reaction (energy barrier: 2.896 kcal/mol). Through Fukui function and frontier molecular orbital analysis, we rigorously elucidated the origin of the highly site-selective C1 reaction. Beyond conventional mechanism elucidation, this study pioneered thermodynamic analysis of the transition state, confirming that its Gibbs free energy decreases significantly with increasing temperature, thereby providing a robust thermodynamic driving force. Furthermore, the study reveals temperature-dependent behavior in specific heat capacity, directly reflecting profound changes in electronic structure from aromatic to sp³ hybridized states and back during the reaction trajectory. This research provides theoretical data supporting the established synergistic insights between kinetics and thermodynamics, paving the way for designing safer, more efficient, and continuous nitration processes