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Mononuclear Heterocyclic Rearrangements. Effect of the Structure of the Side Chain on the Reactivity. Part 3. Rearrangement of Some N-(5-phenyl-1,2,4-oxadiazol-3-yl)-N'-arylformamidines into 1-Aryl-3-benzoylamino-1,2,4-triazoles in Acetonitrile in the Presence of Triethylamine

The apparent pseudo-first-order rate constants for the title reaction give a curvilinear plot versus tertiary amine concentration, according to the equation kA=(ku+K1k2)/(1+K1).This shows the occurrence of two different reaction pathways; the one, independent of and the other, dependent on , which involves a fast conversion of the substrate into an acid-base adduct or an ion pair followed by its slow conversion into the corresponding triazole.The substituent effects on these reactions have also been studied.

Mononuclear Heterocyclic Rearrangements. Effect of the Structure of the Side Chain on the Reactivity. Part 2. Rearrangement of Some N-(5-Phenyl-1,2,4-oxadiazol-3-yl)-N'-arylformamidines into 1-Aryl-3-benzoylamino-1,2,4-triazoles in Dioxane-Water at Various pS+

In the framework of studies concerning the effect of the structure of the side chain mechanism and the reactivity in mononuclear heterocyclic rearrangements, the reactivity of some N-(5-phenyl-1,2,4-oxadiazol-3-yl)-N'-arylformamidines 3 in dioxane-water in the pS+-range 6.0-15.0 was studied and compared with that of arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole 7 and of 3-arylureido-5-phenyl-1,2,4-oxadiazoles 5.A plot of the logarithms of the rate constants versus pS+ showed the occurrence of an uncatalysed (pS+ -independent) and of a catalysed (pS+ -dependent and then pS+ -independent) range.Kinetic data pointed out that the base catalysis is specific, in accord with the relatively high acidity of the formamidines used.The substituent effects on the reactivity were compared with those observed in other mononuclear heterocyclic rearrangements.