Gas-phase pyrolysis of 2-heteroaromatic-1-dimethylaminoethylenes: Kinetic and mechanistic study

Gas-phase pyrolysis reactions of 4(2'-dimethylaminoethenyl)-2-oxo-2H-benzo[ b] pyran-3-carbonitrile (1), 4(2'-dimethylaminoethenyl)-2-oxo-2H-naphtho[1, 2-b]pyran-3-carbonitrile (2), 1,6-dihydro-4-(2'-dimethylaminoethenyl)-6-oxo -1-phenylpyridazine-3,5-dicarbonitrile (3), 2-cyano-5-dimethylamino-3-pheny l-2,4-pentadienonitrile (4), 2-cyano-5-dimethlyamimo-3-(2-thienyl)-2,4-pent adienonitrile (5), 1,2-dihydro-4-(2'-dimethylaminoethenyl)-oxo-quinoline-4- carbonitrile (6), 6-(ethylthio)-4-(2'-dimethylaminoethenyl)-2-phenylpyrimid ine-5-carbonitrile (7) (Scheme 1) have been carried out. The rates of gas-p hase pyrolytic reactions of compounds 3, 4, 5, and 7 have been measured and found to correspond to unimolecular first-order reactions. Product analyse s together with kinetic data were used to outline a feasible pathway for th e pyrolytic reactions of the compounds under study. (C) 2001 John Wiley & S ons, Inc.