Direct Dynamics Study of the Dissociation and Elimination Channels in the Thermal Decomposition of Methyl Nitrite

Combustion and Pyrolysis Kinetics of Chloropicrin

Chloropicrin (CCl₃NO₂) is widely used in agriculture as a pesticide, weed-killer, fungicide or nematicide. It has also been used as a chemical agent during World War I. The precise understanding of its combustion chemistry for destruction processes or in the event of accidental fire of stored reserves is a major safety issue. A detailed chemical kinetic model for the combustion and pyrolysis of chloropicrin is proposed for the first time. A large number of thermo-kinetic parameters were calculated using quantum chemistry and reaction rate theory. The model was validated against experimental pyrolysis data available in the literature. It was shown that the degradation of chloropicrin is ruled by the breaking of the C-N bond followed by the oxidation of the trichloromethyl radical by NO₂ through the formation of the adduct CCl₃ONO, which can decompose to NO, chlorine atom, and phosgene. Phosgene is much more stable than chloropicrin and its decomposition starts at much higher temperatures. Combustion and pyrolysis simulations were also compared and demonstrated that the addition of oxygen has very little effect on the reactivity or product distribution due to the absence of hydrogen atoms in chloropicrin.

A Signature of Roaming Dynamics in the Thermal Decomposition of Ethyl Nitrite: Chirped-Pulse Rotational Spectroscopy and Kinetic Modeling

Chirped-pulse (CP) Fourier transform rotational spectroscopy is uniquely suited for near-universal quantitative detection and structural characterization of mixtures that contain multiple molecular and radical species. In this work, we employ CP spectroscopy to measure product branching and extract information about the reaction mechanism, guided by kinetic modeling. Pyrolysis of ethyl nitrite, CH3CH2ONO, is studied in a Chen type flash pyrolysis reactor at temperatures of 1000-1800 K. The branching between HNO, CH2O, and CH3CHO products is measured and compared to the kinetic models generated by the Reaction Mechanism Generator software. We find that roaming CH3CH2ONO → CH3CHO + HNO plays an important role in the thermal decomposition of ethyl nitrite, with its rate, at 1000 K, comparable to that of the radical elimination channel CH3CH2ONO → CH3CH2O + NO. HNO is a signature of roaming in this system.

A quantum mechanical study on the formation of PCDD/Fs from 2-chlorophenol as precursor

The most direct route to the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in combustion and thermal processes is the gas-phase reaction of chemical precursors such as chlorinated phenols. Detailed insight into the mechanism and kinetics properties is a prerequisite for understanding the formation of PCDD/Fs. In this paper, we carried out molecular orbital theory calculations for the homogeneous gas-phase formation of PCDD/Fs from 2-chlorophenol (2-CP). The profiles of the potential energy surface were constructed, and the possible formation pathways are discussed. The single-point energy calculation was carried out at the MPWB1K/ 6-311+G(3f,2p) level. Several energetically favorable formation pathways were revealed for the first time. The rate constants of crucial elementary steps were deduced over a wide temperature range of 600 approximately 1200 K using canonical variational transition-state theory (CVT) with small curvature tunneling contribution (SCT). The rate-temperature formulas were fitted. The ratio of PCDD to PCDF formed shows strong dependency on the reaction temperature and chlorophenoxy radicals (CPRs) concentration.