RADICAL PATHWAYS IN THE THERMAL-DECOMPOSITION OF PYRIDINE AND DIAZINES - A LASER PYROLYSIS AND SEMIEMPIRICAL STUDY

The mechanisms of thermal decomposition of pyridine and the three isom eric diazines have been investigated by IR laser pyrolysis in conjunct ion with stable end-product analysis by FTIR, NMR and GC-MS, and radic al detection by EPR spectroscopy, Calculations at semi-empirical and a b initio levels have provided confirmation of potential reaction pathw ays, For pyridine, reaction is initiated by formation of pyridyl radic als, as indicated by extensive isotope exchange with added deuterium, Experiments with bromopyridines show that open chain radicals arising from ring opening of 2-pyridyl and 3-pyridyl radicals each lead to sta ble gaseous produces, while 4-pyridyl radicals produce solid deposits, and may be the principal agents in soot formation, The evidence sugge sts that 1,2-diazine decomposes via a molecular route leading to stoic hiometric production of HCN and C2H2, while 1,3- and 1,4-diazine follo w a pattern of H loss and ring radical opening analogous to that of py ridine.