Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

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 k_obs have been adopted to construct the kinetic acidity function H_KM 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 σ_p^- 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 B_Ac2 - the latter appears to be more probable, the splitting of tetrahedral intermediate being its limiting step.