The unimolecular decomposition of dimethoxymethane: channel switching as a function of temperature and pressure

Pazdera, Tobias M; Wenz, Johannes; Olzmann, Matthias

doi:10.1039/d2fd00039c

Cited by 5 publications

(3 citation statements)

References 67 publications

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“…Considering the less than 100 μs residence time of the sample in the heated region of the pyrolysis microreactor, the absolute rate constants are too low to account for the observed conversion of the sample. This is consistent with the findings of Pazdera et al, who calculated dimethoxymethane decomposition rate constants, which also appear to be too low for the reaction to proceed significantly in the heated zone 78 . Photoelectron spectroscopy and dissociative ionization experiments have shown that the rovibrational cooling in the expansion is negligible after the sample leaves the reactor 24 .…”

Section: Resultssupporting

confidence: 90%

“…This is consistent with the findings of Pazdera et al, who calculated dimethoxymethane decomposition rate constants, which also appear to be too low for the reaction to proceed significantly in the heated zone. 78 Photoelectron spectroscopy and dissociative ionization experiments have shown that the rovibrational cooling in the expansion is negligible after the sample leaves the reactor. 24 Therefore, unimolecular reactions may proceed further during the approximately 1 ms collision-free flight time from the reactor exit to the ionization region.…”

Section: Kineticsmentioning

confidence: 99%

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Probing the pyrolysis of ethyl formate in the dilute gas phase by synchrotron radiation and theory

et al. 2023

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The thermal decomposition of the atmospheric constituent ethyl formate was studied by coupling flash pyrolysis with imaging photoelectron photoion coincidence (iPEPICO) spectroscopy using synchrotron vacuum ultraviolet (VUV) radiation at the Swiss Light Source (SLS). iPEPICO allows photoion mass-selected threshold photoelectron spectra (ms-TPES) to be obtained for pyrolysis products. By threshold photoionization and ion imaging, parent ions of neutral pyrolysis products and dissociative photoionization products could be distinguished, and multiple spectral carriers could be identified in several ms-TPES. The TPES and mass-selected TPES for ethyl formate are reported for the first time and appear to correspond to ionization of the lowest energy conformer having a cis (eclipsed) configuration of the O=C(H)-O-C(H 2 )-CH 3 and trans (staggered) configuration of the O=C(H)-O-C(H 2 )-CH 3 dihedral angles. We observed the following ethyl formate pyrolysis products: CH 3 CH 2 OH, CH 3 CHO, C 2 H 6 , C 2 H 4 , HC(O) OH, CH 2 O, CO 2 , and CO, with HC(O)OH and C 2 H 4 pyrolyzing further, forming CO + H 2 O and C 2 H 2 + H 2 . The reaction paths and energetics leading to these products, together with the products of two homolytic bond cleavage reactions, CH 3 CH 2 O + CHO and CH 3 CH 2 + HC(O)O, were studied computationally at the M06-2X-GD3/ aug-cc-pVTZ and SVECV-f12 levels of theory, complemented by further theoretical methods for comparison. The calculated reaction pathways were used to derive Arrhenius parameters for each reaction. The reaction rate constants and branching ratios are discussed in terms of the residence time and newly suggest carbon monoxide as a competitive primary fragmentation product at high temperatures.

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Section: Resultssupporting

confidence: 90%

Section: Kineticsmentioning

confidence: 99%

Probing the pyrolysis of ethyl formate in the dilute gas phase by synchrotron radiation and theory

et al. 2023

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“…We note that this simple picture, which may apply to the pyrolysis of MF (see below), is not generally true. As was shown for the thermal decomposition of dimethoxymethane, complications can arise due to entropic effects, resulting in channel switching from energetically low-lying molecular elimination channels to higher-lying bond dissociation channels with increasing temperature and pressure. We further note that we did not include in our calculations excited electronic states, which were discussed to play a certain role in the combustion chemistry of the OCHO radical. , On the one hand, little is known about the thermochemistry and kinetics of these excited states, and on the other hand, decomposition of OCHO is comparatively fast already in the electronic ground state (see below).…”

Section: Introductionmentioning

confidence: 97%

Pyrolysis of Methyl Formate and the Reaction of Methyl Formate with H Atoms: Shock Tube Experiments and Statistical Rate Theory

et al. 2023

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Methyl formate (MF) is the smallest carboxylic ester and currently considered a promising alternative fuel. It can also serve as a model compound to study the combustion chemistry of the ester group, which is a typical structural feature in many biodiesel components. In the present work, the pyrolysis of MF was investigated behind reflected shock waves at temperatures between 1430 and 2070 K at a nominal pressure of 1.1 bar. Both time-resolved hydrogen atom resonance absorption spectroscopy (H-ARAS) and time-resolved time-of-flight mass spectrometry (TOF-MS) were used for species detection. Additionally, the reaction of MF and perdeuterated MF-d 4 with H atoms was investigated at temperatures between 1000 and 1300 K at nominal pressures of 0.4 and 1.1 bar with H-ARAS. In the latter experiments, ethyl iodide served as precursor for H atoms. Rate coefficients of seven parallel unimolecular decomposition channels of MF and five parallel reaction channels of the MF + H reaction were calculated from statistical rate theory on the basis of molecular and transition state data from quantum chemical calculations. These calculated rate coefficients were implemented into an MF pyrolysis/oxidation mechanism from the literature, and the experimental concentration–time profiles of H (from ARAS) as well as MF, CH3OH, HCHO, and CO (from TOF-MS) were modeled. It turned out that the literature mechanism, which was originally validated against flow-reactor experiments, ignition delay times, and laminar burning velocities, was generally able to fit also the concentration–time profiles from the shock tube experiments reasonably well. The agreement could still be improved by substituting the original rate coefficients, which were estimated from structure–reactivity relationships, by the values calculated from statistical rate theory in the present work. Details of the channel branching are discussed, and the updated mechanism is given, also in machine-readable form.

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The Unimolecular Decomposition Mechanism of Trimethyl Phosphate

Kanayama,

Nakamura,

Maruta

et al. 2024

Chemistry A European J

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Trimethyl phosphate (TMP), an organophosphorus compound (OPC), is a promising fire‐retardant candidate for lithium‐ion battery (LIB) electrolytes to mitigate fire spread. This study aims to understand the mechanism of TMP unimolecular thermal decomposition to support the integration of a TMP chemical kinetic model into a LIB electrolyte surrogate model. Reactive intermediates and products of TMP thermal decomposition were experimentally detected using vacuum ultraviolet (VUV) synchrotron radiation and double imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy. Phosphorus‐containing intermediates such as PO, HPO and HPO2 were identified. Sampling effects could successfully be obviated thanks to photoion imaging, which also showed evidence for isomerization reactions upon wall collisions in the ionization chamber. Quantum chemical calculations performed for the unimolecular decomposition of TMP revealed for the first time that isomerization channels via hydrogen and methyl transfer (barrier heights of 65.9 and 72.6 kcal/mol, respectively) are the lowest‐energy primary steps of TMP decomposition followed by CH3OH/CH3/CH2O or dimethyl ether (DME) production, respectively. We found an analogous DME production channel in the unimolecular decomposition of dimethyl methylphosphonate (DMMP), another important OPC fire‐retardant additive with a similar molecular structure to TMP, which are not included in currently available chemical kinetic models.

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The unimolecular decomposition of dimethoxymethane: channel switching as a function of temperature and pressure

Abstract: Branching ratios of competing unimolecular reactions often exhibit a complicated temperature and pressure dependence that makes modeling of complex reaction systems in the gas phase difficult. In particular, the competition...

Cited by 5 publications

References 67 publications

Probing the pyrolysis of ethyl formate in the dilute gas phase by synchrotron radiation and theory

Probing the pyrolysis of ethyl formate in the dilute gas phase by synchrotron radiation and theory

Pyrolysis of Methyl Formate and the Reaction of Methyl Formate with H Atoms: Shock Tube Experiments and Statistical Rate Theory

The Unimolecular Decomposition Mechanism of Trimethyl Phosphate

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