KINETICS OF PYROLYSIS OF A COAL MODEL-COMPOUND, 2-PICOLINE, THE NITROGEN HETEROAROMATIC ANALOG TO TOLUENE .2. THE 2-PICOLYL RADICAL AND KINETIC MODELING

The pyrolysis of 2-picoline, investigated experimentally in our previous paper,1 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 feasibility of this mechanism by predicting the observed profiles for 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 inference is supported by the "normal" value of the rate constant for 2-picolyl + H recombination found by modeling to be in the range 1 x 10(13)-6 x 10(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.