Reactions of HO2 with n-propylbenzene and its phenylpropyl radicals

Abstract

Abstraction of an H atom from the propyl side chain by hydroperoxyl radicals (HO 2 ) constitutes a central reaction in the low-temperature oxidation of n-propylbenzene (nPB).Herein, we calculate reaction rate constants for H abstraction from primary, secondary and benzylic sites in nPB. Rate of abstraction of a benzylic H atom dominates that of a secondary H atom with negligible abstraction of the primary H atom at T ≥ 600 K. We present the reaction enthalpies for 1-phenyl-1-propyl (R1), 1-phenyl-2-propyl (R2) and 1-phenyl-3-propyl (R3) radicals, and compare the computed reaction rate constants and bond dissociation enthalpies with analogous scarce literature values. Addition of HO 2 radicals to radical sites in R1, R2 and R3 proceeds in a highly exothermic process and results in the formation of HO 2 -phenylpropyl adducts. Mapped potential energy surfaces illustrate all plausible exit channels of the three HO 2 -phenylpropyl adducts. Master equation calculations for the three phenylpropyl + HO 2 reactions indicate that direct O-OH bond fission and water elimination control the fate of the adducts leading to the formation of ketonic-type structures. Results from this study should be useful to update kinetic models for the low-temperature oxidation of alkylbenzenes in general.

Oxidation of Polyethylene under Corrosive NOx Atmosphere

“…As it is the case for alkanes, reactions of H/O radicals with PE may also generate free alkyl sites. At lower temperatures, hydroperoxyl radicals play a crucial role in driving the low-temperature oxidation cycle. , In subsequent steps, hydroxyl and hydroperoxyl radicals could add to vacant radical sites in the PE chain. Consequently, oxidation of PE produces three main radical-type species; namely, alkyl, hydroxyalkyl and hydroperoxyalkyl .…”

Reaction of Hydroperoxy Radicals with Primary C1–5 Alcohols: A Profound Effect on Ignition Delay Times

“…15 Likewise, we have utilized density functional theory (DFT) calculations and chemistry models to compute rate constants for H abstraction by HO 2 from a large array of compounds including methanol, 18 benzene, 19 mercaptans, 20 and alkylated benzenes. 21,22 Despite the progress on the theoretical side, the literature presents a rather limited account of kinetics data germane to H abstraction by HO 2 from an important fuel's category, that is, alcohols. Alcohols are important non-petroleum fuels on their own right or when blended with other hydrocarbon fuels.…”

High-Pressure-Limit and Pressure-Dependent Rate Rules for Unimolecular Reactions Related to Hydroperoxy Alkyl Radicals in Normal Alkyl Cyclohexane Combustion. 1. Concerted HO2 Elimination Reaction Class and β-Scission Reaction Class

“…All the electronic structure (i.e., reactants, products, and transition states) calculations are performed by using the CBS-QB3 composite method as implemented in the Gaussian 09 program . CBS-QB3 calculations have been shown to predict enthalpies of formation for a large test set of molecules with an accuracy of about 1.5 kcal mol –1 , and they have been successfully applied in numerous kinetic studies. − The CBS-QB3 method is based on geometry optimization as well as vibrational frequency analysis of molecules at the B3LYP/CBSB7 level of theory, and the Cartesian coordinates of all optimized structures in this work are provided in Supporting Information-I. Transition states are verified by the presence of a single imaginary frequency corresponding to the reaction path and intrinsic reaction coordinate calculations performed at the same level of theory.…”