Exploring the Ab Initio Kinetics of Trimethyl Phosphite

Résumé fourni par la source

Trimethyl phosphite (TMPI) is an organophosphorus compound of growing interest in the contexts of fire safety and energetic materials. Yet, its gas-phase combustion kinetics remain largely underexplored. We develop a TMPI kinetic mechanism from first-principles quantum chemistry and master-equation (RRKM/MESS) calculations, supported by reactive molecular dynamics (ReaxFF-MD) to map early time bond activation and product growth. The potential-energy surfaces include C–O and P–O homolysis, hydrogen-atom abstraction (HAA) by Ḣ, ȮH, HȮ 2, ĊH 3, and CH 3 Ȯ, and O 2, intramolecular H-transfer, and key association or isomerization steps. Thermochemistry (ΔHf°, S, c p ) and NASA polynomials are provided for all P-bearing intermediates. The model reproduces the expected Arrhenius behavior of ignition delay times (IDTs) for TMPI/air across a temperature range of 900–1500 K and pressures of 1 and 10 bar, with φ values ranging from 0.5 to 2.0. Increasing temperature and pressure shorten the IDT, with richer mixtures igniting faster. Sensitivity and flux analyses identify high-temperature chain branching (H + O 2 ⇌ O + OH) and control of the HO 2 /OH pools as primary rate-controlling features, while TMPI–radical reactions that convert radicals to stable products inhibit ignition. Flux maps show HAA-initiated TMPI_R as the universal entry to the radical pool and reveal PO 2 as a central hub that feeds PO, HOPO/HOPO 2, and ultimately PO 3 . Hybrid NVT+NVE MD trajectories further indicate an earlier onset of decomposition under adiabatic conditions, consistent with the rapid amplification of radicals once local hot spots are not thermostat-damped. The resulting mechanism and thermochemical set provide a consistent foundation for modeling phosphite oxidation and for comparing phosphite, phosphate, and phosphonate chemistries in fire-inhibition strategies.

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