Theoretical study of hydrogen abstraction by small radicals from cyclohexane-carbonyl-hydroperoxide

Abstract

Hydrogen abstraction from carbonyl-hydroperoxide is a new reaction class in the low-temperature oxidation of hydrocarbons. In this work, a comprehensive study to the kinetics for the hydrogen abstraction from cyclohexane-carbonyl-hydroperoxide (CCHP) is investigated using the CBS-QB3 composite method. Five small active radicals (H, CH3, O (3P), OH and HO2) are selected as the extracting agents, and the corresponding barrier heights are computed. Guided by the reaction barriers, the preferable path on hydrogen abstraction from CCHP is identified. The two-transition-state model is employed to obtain the overall rate constant when HO2 and OH act as the extracting agents due to the formation of reactant and product complexes. High-pressure-limit rate constants for 25 elementary reactions are reported in the modified Arrhenius form. Branching ratios for the site-specific hydrogen abstraction reactions ranging from 300 to 2500 K are illustrated to show the temperature dependence of preferable path. Compared with the theoretical rate constants obtained in this work, the values estimated by using analogy rules have obvious deviations at low temperature. The obtained hydrogen abstraction reactions are added to the JetSurF2.0 mechanism, thereby improving its kinetic modeling results for cyclohexane oxidation. Present work provides accurate kinetic parameters for this new type of reaction class which can be helpful to improve the predictive capability for hydrocarbon mechanism.