Thermal Decomposition of 3-Bromopropene. A Theoretical Kinetic Investigation

Abstract

A detailed kinetic study of the gas-phase thermal decomposition of 3-bromopropene over wide temperature and pressure ranges was performed. Quantum chemical calculations employing the density functional theory methods B3LYP, BMK, and M06-2X and the CBS-QB3 and G4 ab initio composite models provide the relevant part of the potential energy surfaces and the molecular properties of the species involved in the CH2═CH-CH2Br → CH2═C═CH2 + HBr (1) and CH2═CH-CH2Br → CH2═CH-CH2 + Br (2) reaction channels. Transition-state theory and unimolecular reaction rate theory calculations show that the simple bond fission reaction ( 2 ) is the predominant decomposition channel and that all reported experimental studies are very close to the high-pressure limit of this process. Over the 500-1400 K range a rate constant for the primary dissociation of k2,∞ = 4.8 × 10(14) exp(-55.0 kcal mol(-1)/RT) s(-1) is predicted at the G4 level. The calculated k1,∞ values lie between 50 to 260 times smaller. A value of 10.6 ± 1.5 kcal mol(-1) for the standard enthalpy of formation of 3-bromopropene at 298 K was estimated from G4 thermochemical calculations.

Quantum-Chemical Kinetic Study of the Unimolecular Decomposition Reactions of 1-Bromo-3-Chloropropane

“…Table presents the corresponding reaction enthalpies at 0 and 298 K calculated for reactions to using the standard enthalpy of formation for 1-bromo-3-chloropropane derived here, and reported values for the other involved species (in kcal mol –1 ):–8.47 ± 0.03 (HBr), −22.030 ± 0.001 (HCl), 26.733 ± 0.013 (Br), 28.992 ± 0.001 (Cl), 10.6 ± 1.5 (BrCH 2 CHCH 2 ), and −0.4 ± 1.5 (ClCH 2 CHCH 2 ) . In addition, enthalpies of reaction at 0 and 298 K for reactions to calculated directly from total electronic energies corrected for zero-point energies at the MN15/6-311++G­(3df,3pd) and G4 levels of theory are presented in Table .…”

“…The calculations predict, in both cases, four-center transition states (see Figure ) with comparative barriers values Δ H # 0 (at 0 K) ranging from 52 to 58 kcal mol –1 . Similar structures were previously observed in the transition states corresponding to elimination reactions of 3-bromopropene, 3-cloropropeno, 2-bromopropene, and 2-cloropropeno. − Additionally, geometrical parameters of the products of both elimination reactions are listed in Table S2 of the Supporting Information.…”

“…Thus, channels and are energetically competitive, and both may be plausible reaction channels. The energetics of the subsequent decomposition of CH 2 CHCH 2 Cl and BrCH 2 CHCH 2 have been previously studied. − …”

Role of the Recombination Channel in the Reaction between the HO and HO2 Radicals

“…The procedure to estimate SACM/CT high pressure rate coefficients has been described previously. , It has been demonstrated that the high pressure rate coefficients can be factorized as …”

Thermochemistry and Kinetics of the Thermal Decomposition of 1‐Chlorohexane

“…The kinetics of the thermal decomposition of halogenated compounds has been the subject of different investigations for several decades . Experimental and theoretical studies have been motivated not only by the interest in the environmental impact of these species but also by a desire to understand the reaction mechanisms involved.…”