Computational Tests of Models for Kinetic Parameters of Unimolecular Reactions of Organophosphorus and Organosulfur Compounds

Hahn, David K.; RaghuVeer, Krishans S.; Ortiz, J. V.

doi:10.1021/jp206344r

Cited by 6 publications

(6 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To begin, it has been proposed experimentally and theoretically that the primary pyrolytic destruction step for DIMP and other similar molecules is a unimolecular decomposition to IMP and propene via a six-membered ring transition state. ,− Moreover, propene production has been observed under a variety of high-temperature conditions, beginning with temperatures as low as 700 K, which is lower than the ablation range studied here. , In vacuum studies, propene is also produced as a result of dissociative adsorption of DIMP. , Essentially, many studies agree that a major step in DIMP destruction involves the formation of propene. On the other hand, few studies have identified direct mechanisms that yield smaller substituted products from DIMP’s initial dissociation (and indeed no single initial bond scission is enough to yield a two-carbon product from DIMP directly).…”

Section: Results and Discussionmentioning

confidence: 73%

Rapid Laser-Induced Temperature Jump Decomposition of the Nerve Agent Simulant Diisopropyl Methylphosphonate under Atmospheric Conditions

et al. 2019

View full text Add to dashboard Cite

We present work detailing the destruction of the nerve agent simulant diisopropyl methylphosphonate (DIMP) via rapid laser heating under atmospheric conditions. Following Nd:YAG laser ablation of liquid DIMP deposited on a graphite substrate, both parent and product fragments are transmitted via capillary from an atmospheric chamber to a vacuum chamber containing a high-resolution mass spectrometer. This allows for real-time measurements of product distributions under a variety of temperature and atmospheric conditions. Ex situ Fourier transform infrared (FTIR) spectroscopy analysis of the same chamber contents provides complementary information about product identities and fragmentation pathways. Results demonstrate that product distributions depend on heating rate, surface temperature, and atmospheric oxygen content. In the destruction of the DIMP, the relative yields of alkene products depends significantly on laser power; smaller products are relatively more abundant at higher ablation temperatures. We also show that in the absence of atmospheric oxygen, the concentration of oxygenated products decreases sharply relative to alkene and alkane products. This suggests that under high-temperature conditions, atmospheric oxygen is incorporated directly into the products of the fragmented simulant. This project extends significantly our understanding of the fundamental chemistry of these dangerous compounds under atmospheric and rapidly changing thermal conditions. The results have critical implications for the development of effective chemical warfare agent decontamination and destruction strategies.

show abstract

Section: Results and Discussionmentioning

confidence: 73%

Rapid Laser-Induced Temperature Jump Decomposition of the Nerve Agent Simulant Diisopropyl Methylphosphonate under Atmospheric Conditions

et al. 2019

View full text Add to dashboard Cite

show abstract

“…Zegers and Fisher measured this unimolecular decomposition by following decay of TEP during its pyrolysis in a flow reactor within a narrow T range of 706–854 K. On the basis of Zegers and Fisher’s experimental measurement and using analogy with ester and DEMP decomposition reactions that involve same kind of transition state, Glaude et al , estimated the rate in LLNL kinetic model (given in Table ). More recently, Hahn et al used ab initio calculations to compute kinetic parameters for the reaction at temperature of 570–940 K using two levels of theory, namely, CVT/SCT and VTST-ISPE/SCT. Results from CVT/SCT calculations were more in agreement with experiment/estimated values ( k cal / k expt at 700 K < 6.2) than VTST-ISPE/SCT calculations ( k cal / k expt > 20).…”

Section: Resultsmentioning

confidence: 99%

Shock Tube/Laser Absorption and Kinetic Modeling Study of Triethyl Phosphate Combustion

et al. 2018

View full text Add to dashboard Cite

Pyrolysis and oxidation of triethyl phosphate (TEP) were performed in the reflected shock region at temperatures of 1462-1673 K and 1213-1508 K, respectively, and at pressures near 1.3 atm. CO concentration time histories during the experiments were measured using laser absorption spectroscopy at 4580.4 nm. Experimental CO yields were compared with model predictions using the detailed organophosphorus compounds (OPC) incineration mechanism from the Lawrence Livermore National Lab (LLNL). The mechanism significantly underpredicts CO yield in TEP pyrolysis. During TEP oxidation, predicted rate of CO formation was significantly slower than the experimental results. Therefore, a new improved kinetic model for TEP combustion was developed, which was built upon the AramcoMech2.0 mechanism for C-C chemistry and the existing LLNL submechanism for phosphorus chemistry. Thermochemical data of 40 phosphorus (P)-containing species were reevaluated, either using recently published group values for P-containing species or by quantum chemical calculations (CBS-QB3). The new improved model is in better agreement with the experimental CO time histories within the temperature and pressure conditions tested in this study. Sensitivity analysis was used to identify important reactions affecting CO formation, and future experimental/theoretical studies on kinetic parameters of these reactions were suggested to further improve the model. To the best of our knowledge, this is the first study of TEP kinetics in a shock tube under these conditions and the first time-resolved laser-based species time history data during its pyrolysis and oxidation.

show abstract

“…Quantum chemical calculations have been used to determine mainly thermochemical properties [17,18], but also rate constants of molecular systems containing trivalent or pentavalent phosphorus [19]. Sullivan et al [20] investigated the combustion of methylphosphonic acid (MPA) at the CBS-Q level of theory and evaluated several elementary reactions, such as the unimolecular decomposition of MPA and the hydrogen abstraction from MPA by OH radicals.…”

Section: Introductionmentioning

confidence: 99%

The decisive role of pericyclic reactions in the thermal decomposition of organophosphorus compounds

Lizardo-Huerta

Sirjean

Verdier³

et al. 2021

Proceedings of the Combustion Institute

View full text Add to dashboard Cite

The understanding of the thermal decomposition chemistry of chemical warfare nerve agents is largely limited by the scarcity of kinetic data. Because of the high toxicity of these molecules, experimental determination of their chemical properties is very difficult. In the present work, a comprehensive detailed kinetic model for the decomposition of sarin and some simulants, i.e. di-isopropyl methyl phosphonate (DIMP), diethyl methylphosphonate (DEMP), and triethyl phosphate (TEP) were developed, containing possible molecular and radical pathways. The importance of unimolecular pericyclic decomposition led to evaluate precisely the rate constants of these reactions with high level theoretical calculations. The QCISD(T)/cc-PV∞QZ//B2PLYPD3/6-311+G(2d,d,p) level of theory was selected after a benchmark. The contribution of hindered rotors was included with the 1D-HR-U approach.Tunneling was taken into account for H-atom transfer. Transition state theory was used to calculate high-pressure limit rate constants and pressure dependent rate constants were calculated using Master Equation modelling. The model was validated against experimental pyrolysis and oxidation experimental data available in literature. Flux analyses showed that whatever the conditions are, the first step of decomposition of the studied phosphorus compounds are pericyclic eliminations leading to successive decompositions, whereas bondbreaking or H-atom abstraction remain negligible, even at high temperature.

show abstract

Computational Tests of Models for Kinetic Parameters of Unimolecular Reactions of Organophosphorus and Organosulfur Compounds

Cited by 6 publications

References 33 publications

Rapid Laser-Induced Temperature Jump Decomposition of the Nerve Agent Simulant Diisopropyl Methylphosphonate under Atmospheric Conditions

Rapid Laser-Induced Temperature Jump Decomposition of the Nerve Agent Simulant Diisopropyl Methylphosphonate under Atmospheric Conditions

Shock Tube/Laser Absorption and Kinetic Modeling Study of Triethyl Phosphate Combustion

The decisive role of pericyclic reactions in the thermal decomposition of organophosphorus compounds

Contact Info

Product

Resources

About