skip to main content

SciTech ConnectSciTech Connect

Title: Ab initio study of the kinetics of hydrogen abstraction reactions on toluene and tetralin

Hydrogen abstraction reactions play a key role in many thermal and catalytic processes involved in the production of fuels and chemicals. In this paper, the reaction barriers and rate constants for the hydrogen abstraction reactions on toluene and tetralin by the benzyl radical are calculated by ab initio methods. These reactions are representatives of similar reactions occurring in the thermolysis of lignin model compounds containing the phenethyl phenyl ether (PPE) structural moiety. Thermolysis of PPE occurs by a free radical chain mechanism in which the product selectivity arises from competitive hydrogen abstraction at the benzylic and nonbenzylic methylen sites by chain carrying benzyl and phenoxyl radicals. The title reactions serve to calibrate the theoretical methods to be used in the study of PPE through comparison of the rate constants and the reaction enthalpies with reliable experimental values. In this study, we used two different hybrid density functionals (BHandHLYP, B3LYP) and second-order perturbation theory to obtain equilibrium and transition state geometries. Multiple transition states were found for both reactions. BHandHLYP underestimates and second-order perturbation theory overestimates the reaction barriers; B3LYP energy barriers agree well with experiment. Absolute and relative rate constants were calculated using transition state theory. We found that themore » relative rate constant using the B3LYP functional agrees within a factor of 2.0 with experiment at the experimental temperature of 333 K, indicating that the B3LYP functional will be successful in predicting relative rate constants for hydrogen abstraction reactions participating in the pyrolysis of PPE.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [1]
  1. ORNL
Publication Date:
OSTI Identifier:
930762
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Molecular Structure (Theochem); Journal Volume: 851; Journal Issue: 1-3
Research Org:
Oak Ridge National Laboratory (ORNL); Center for Computational Sciences
Sponsoring Org:
SC USDOE - Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 09 BIOMASS FUELS; BENZYL RADICALS; CHAINS; FUNCTIONALS; HYDROGEN; KINETICS; LIGNIN; PERTURBATION THEORY; PHENYL ETHER; PRODUCTION; PYROLYSIS; RADICALS; TETRALIN; TOLUENE