Collect. Czech. Chem. Commun. 1990, 55, 2468-2474

Synthesis and cyclization kinetics and mechanism of 1-(2-ethoxycarbonylphenyl)-3-aryltriazenes. Kinetic acidity function of sodium methoxide in methanol

Oldřich Pytela and Vladimír Dlouhý

Department of Organic Chemistry, Institute of Chemical Technology, 532 10 Pardubice


Eight 1-(2-ethoxycarbonylphenyl)-3-aryltriazenes have been synthetized and the rate constants of their sodium-methoxide-catalyzed cyclization have been measured in methanol at 25 °C. The experimental rate constants kobs have been adopted to construct the kinetic acidity function HKM which has been shown to be identical with the -log[CH3O-] values. Two mathematical procedures have been used to determine the catalytic rate constants and their dependence on the Hammett substituent constants. A closer dependence is obtained with the σ values than with the σp- values. The ρ value found (0.3) indicates a compensation of the substituent effects upon the dissociation of the starting triazene and upon the subsequent reaction of the conjugated base. Out of the two mechanistic alternatives - E1cB and BAc2 - the latter appears to be more probable, the splitting of tetrahedral intermediate being its limiting step.