Context In this work, the mechanism and kinetics of the p-toluidine + NH2 reaction have been thoroughly investigated. The computed results indicate that H-abstraction channels are significantly more favorable than NH2-addition pathways over the entire temperature range examined. In particular, the route leading to product PR1 (C6H4(CH3)NH•) is the dominant reaction channel, contributing approximately 49–64% to the overall product distribution from 300 to 2000 K. The fate of the main product PR1 is then discussed when reacting with an O2 molecule. Among the addition pathways, the formation of the IS2 (o-C6H4(CH3)(NH2)NH2) adduct is the most competitive, accounting for 19–32% of the products at low temperatures (300–700 K). At higher temperatures (800–2000 K), the H-abstraction channel generating PR4 ((CH2•)C6H4NH2) becomes increasingly important, with branching ratios of 14.5–22.5%. H-abstraction at the ortho and meta positions contributes negligibly at low and intermediate temperatures (T ≤ 1000 K), but their branching ratios rise substantially at elevated temperatures, reaching 4–12% and 5–16%, respectively. All remaining channels exhibit minor contributions (≤ 3%) and do not significantly affect the overall product distribution. A comparison with related systems, namely the m-toluidine + NH2 and p-toluidine + OH reactions, shows that the H-abstraction pattern in this work is similar to that of the m-toluidine + NH2 system, but the dominance of abstraction pathways is less pronounced than in the p-toluidine + OH reaction. Collectively, these findings validate the reliability of the computational methodology and provide valuable kinetic parameters and mechanistic insights for modeling the reactivity of toluidine-derived aromatic amines in both atmospheric and combustion environments. Methods All reactants, transition states, intermediates, and products associated with the p-toluidine + NH2 system were fully optimized at the M06-2X density functional level in combination with the aug-cc-pVTZ basis set. More accurate electronic energies were subsequently obtained from single-point calculations using the CCSD(T) method. Rate constants for the H-abstraction channels were evaluated within the framework of conventional transition-state theory (TST) employing the ChemRate code, whereas the pressure-dependent kinetics of the NH2-addition pathways were determined through RRKM/master-equation simulations carried out with the MESMER program. All electronic structure calculations were performed with the Gaussian 16 suite.

Mechanistic and Kinetic Insights into the Gas-Phase Reaction of p-Toluidine with Amino Radicals: A High-Level Theoretical Study

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发表日期：

2026年2月17日

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Hoang T. T. Trang,
Tue N. Nguyen,
Nghia T. Nguyen,
Tien V. Pham

摘要

Context

In this work, the mechanism and kinetics of the p-toluidine + NH₂ reaction have been thoroughly investigated. The computed results indicate that H-abstraction channels are significantly more favorable than NH₂-addition pathways over the entire temperature range examined. In particular, the route leading to product PR₁ (C₆H₄(CH₃)NH^•) is the dominant reaction channel, contributing approximately 49–64% to the overall product distribution from 300 to 2000 K. The fate of the main product PR₁ is then discussed when reacting with an O₂ molecule. Among the addition pathways, the formation of the IS2 (o-C₆H₄(CH₃)(NH₂)NH₂) adduct is the most competitive, accounting for 19–32% of the products at low temperatures (300–700 K). At higher temperatures (800–2000 K), the H-abstraction channel generating PR₄ ((CH₂^•)C₆H₄NH₂) becomes increasingly important, with branching ratios of 14.5–22.5%. H-abstraction at the ortho and meta positions contributes negligibly at low and intermediate temperatures (T ≤ 1000 K), but their branching ratios rise substantially at elevated temperatures, reaching 4–12% and 5–16%, respectively. All remaining channels exhibit minor contributions (≤ 3%) and do not significantly affect the overall product distribution. A comparison with related systems, namely the m-toluidine + NH₂ and p-toluidine + OH reactions, shows that the H-abstraction pattern in this work is similar to that of the m-toluidine + NH₂ system, but the dominance of abstraction pathways is less pronounced than in the p-toluidine + OH reaction. Collectively, these findings validate the reliability of the computational methodology and provide valuable kinetic parameters and mechanistic insights for modeling the reactivity of toluidine-derived aromatic amines in both atmospheric and combustion environments.

Methods

All reactants, transition states, intermediates, and products associated with the p-toluidine + NH₂ system were fully optimized at the M06-2X density functional level in combination with the aug-cc-pVTZ basis set. More accurate electronic energies were subsequently obtained from single-point calculations using the CCSD(T) method. Rate constants for the H-abstraction channels were evaluated within the framework of conventional transition-state theory (TST) employing the ChemRate code, whereas the pressure-dependent kinetics of the NH₂-addition pathways were determined through RRKM/master-equation simulations carried out with the MESMER program. All electronic structure calculations were performed with the Gaussian 16 suite.