THE PYROLYSIS OF 3-PICOLINE - AB-INITIO QUANTUM-CHEMICAL AND EXPERIMENTAL (SHOCK-TUBE) KINETIC-STUDIES

The pyrolysis of 3-picoline dilute in argon was investigated using a s ingle-pulse shock tube over the temperature range of 1400-1650 K and t otal pressures of 12-13 atm. The principal products observed were HCN, acetylene, benzene, cyanoacetylene, methane, and pyridine. Assuming t hat 3-picoline decomposes according to first-order kinetics, the rate constant for its overall disappearance was determined to be k(dis) = 1 0(16.9(+/- 0.8)) exp[-99 (+/- 6) kcal mol(-1)/RT] s(-1). The principal initial decomposition routes were found to be via the formation of th e 3-picolyl and m-pyridyl radicals whose subsequent ring-opening led t o the observed products. A 68-step kinetic model was developed that su ccessfully fits the experimental data. The dominant reactions, i.e., t he formation of picolyl and pyridyl radicals and their subsequent chai n-opening reactions, were studied using ab initio quantum chemical tec hniques. The ab initio data were also incorporated into the kinetic mo del in the form of energies and A-factors for reactions for which no k inetic or thermochemical data were previously available. Optimization of the kinetic model yields a value of 64 +/- (3) kcal mol(-1) for the heat of formation of 3-picolyl, a value lower than that for 2-picolyl , suggesting that the decomposition of 3-picoline more closely resembl es that of toluene, rather than its isomer 2-picoline.