Gas‐phase thermolysis of benzotriazole derivatives: part 1—synthesis of α‐<i>N</i>(1)‐ and<i>N</i>(2)‐benzotriazolyl ketones and kinetics and mechanism of their gas‐phase pyrolysis

Abstract

Abstract 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 © 2004 John Wiley &amp; Sons, Ltd.