Kinetics of Pyrolysis of a Coal Model Compound, 2-Picoline, the Nitrogen Heteroaromatic Analogue of Toluene. 2. The 2-Picolyl Radical and Kinetic Modeling

Article abstract of DOI:10.1021/j100204a045

The pyrolysis of 2-picoline, investigated experimentally in our previous paper, has been successfully modeled using a 70-reaction free-radical mechanism.The mechanism includes decomposition pathways for o-pyridyl and 2-picolyl, both of which are formed through the principal initiation reactions of 2-picoline.The proposed mechanism for 2-picolyl decomposition involves the direct ring opening of the 2-picolyl radical.Further reactions of the open chain isomer of 2-picolyl resulted in the formation of the major products HCN and acetylene and the minor products 1-cyanocyclopentadiene and cyclopentadiene.Kinetic modeling confirmed the feasability of this mechanism by predicting the observed profiles of these species.Optimizing of the heat of formation of 2-picolyl through kinetic modeling resulted in a value of 68 (+/-5) kcal mol^-1.This value suggests a lower level of resonance stabilization for 2-picolyl compared to benzyl.This interference is supported by the "normal" value of the rate constant for 2-picolyl + H recombination found by modeling to be in the range 1x10^-13-6x10^-13 cm³ mol^-1 s^-1.The reactant and product profiles predicted by the kinetic model were found to be very sensitive to the rate of the initiation reaction yielding methyl and o-pyridyl radicals, allowing the heat of formation of the o-pyridyl radical to be determined.The optimized rate constant for this initiation reaction was found to be 10^16.1(+/-0.2) exp (-91.5 (+/-2) kcal mol^-1/RT) s^-1, corresponding to a heat of formation for the o-pyridyl radical of 84.1 (+/-2) kcal mol^-1.