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 × 1014 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.