Gas-phase thermolysis of benzotriazole derivatives:: part 1 -: synthesis of α-N(1)- and N(2)-benzotriazolyl ketones and kinetics and mechanism of their gas-phase pyrolysis

1-(Benzotriazol-1-yl)propan-2-one (1) and 3-(benzotriazol-1-yl)butan-2-one (2), and their respective phenyl analogues 2-(benzotriazol-1-yl)-1-phenylethanone (3) and 2-(benzotriazol-1-yl)-1-phenylpropan-1-one (4), together with 1-cyanobenzotriazole (5) and 1-(benzotriazol-2-yl)propan-2-one (6), were synthesized and then subjected to gas-phase thermolysis. The products of complete pyrolysis of 1-4 were found to be aniline in addition to either 2-substituted indoles or 2,3-disubstituted indoles. The kinetics of the gas-phase thermal elimination reactions of the present compounds were also studied, the first such investigation on benzotriazoles. The Arrhenius pre-exponential factor (A/s(-1)) and activation energy (E-a/kJ mol(-1)) are, respectively: 10.03 and 156.7 for (1), 9.93 and 158.0 for (2), 12.68 and 169.9 for (3), 9.45 and 144.4 for (4) and 15.40 and 163.6 for (5). Compound 6 appeared to have isomerized by a thermally allowed 1,5-group migration into 1 prior to thermolysis. The results of the kinetic and product analysis are rationalized with reference to a mechanism involving extrusion of a stable (N-2) molecule and formation of a reactive 1,3-biradical intermediate, which in turn rearranges into the final products of reaction. Copyright (C) 2004 John Wiley Sons, Ltd.