Substitution Reactions in the Pyrolysis of Acetone Revealed through a Modeling, Experiment, Theory Paradigm

Abstract

The development of high-fidelity mechanisms for chemically reactive systems is a challenging process that requires the compilation of rate descriptions for a large and somewhat ill-defined set of reactions. The present unified combination of modeling, experiment, and theory provides a paradigm for improving such mechanism development efforts. Here we combine broadband rotational spectroscopy with detailed chemical modeling based on rate constants obtained from automated ab initio transition state theory-based master equation calculations and high-level thermochemical parametrizations. Broadband rotational spectroscopy offers quantitative and isomer-specific detection by which branching ratios of polar reaction products may be obtained. Using this technique, we observe and characterize products arising from H atom substitution reactions in the flash pyrolysis of acetone (CH 3 C(O)CH 3 ) at a nominal temperature of 1800 K. The major product observed is ketene (CH 2 CO). Minor products identified include acetaldehyde (CH 3 CHO), propyne (CH 3 CCH), propene (CH 2 CHCH 3 ), and water (HDO). Literature mechanisms for the pyrolysis of acetone do not adequately describe the minor products. The inclusion of a variety of substitution reactions, with rate constants and thermochemistry obtained from automated ab initio kinetics predictions and Active Thermochemical Tables analyses, demonstrates an important role for such processes. The pathway to acetaldehyde is shown to be a direct result of substitution of acetone's methyl group by a free H atom, while propene formation arises from OH substitution in the enol form of acetone by a free H atom.

Reactions of NO<sub>3</sub> with aromatic aldehydes: gas-phase kinetics and insights into the mechanism of the reaction

“…Methyl methacrylate, MMA, was used as the reference compound in this work because the rate coefficient at 298 K for its reaction with the NO 3 radical has been measured in the same chamber using the same method as used here (Zhou et al, 2017) to be k MMA = (2.98±0.35)×10 −15 cm 3 molec. −1 s −1 .…”

“…The method used to analyze the temporal profiles of NO 3 and N 2 O 5 to obtain k 1 -k 7 has been described by Zhou et al (2017Zhou et al ( , 2019. Figure 2 shows an example of the temporal profiles of NO 3 and N 2 O 5 for Reaction (R1) from which the rate coefficient k 1 was derived.…”

“…The kinetics and products were studied in a 7300 L indoor simulation chamber described in detail previously (Zhou et al, 2017); therefore, it is described only briefly here. The chamber was made of Teflon foil.…”

“…Experiments were conducted in the same 7300 L simulation chamber described in the previous section. The temporal profiles of NO 3 and N 2 O 5 were measured using CRDS in an excess of each aromatic aldehyde (Zhou et al, 2017). They were simultaneously fit to a reaction scheme (see below) to extract the reaction rate coefficient as described by Zhou et al (2017).…”

“…The temporal profiles of NO 3 and N 2 O 5 were measured using CRDS in an excess of each aromatic aldehyde (Zhou et al, 2017). They were simultaneously fit to a reaction scheme (see below) to extract the reaction rate coefficient as described by Zhou et al (2017). The typical experimental procedure consisted of the following steps:…”