Mononuclear heterocyclic rearrangements. Part 9. A kinetic study of the rearrangement of the Z-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into 4-benzoylamino-2,5-diphenyl-1,2,3-triazole in methanol, dioxan, ethyl acetate, and acetonitrile

Abstract

The kinetics of the title reactions have been measured at various piperidine concentrations. The results obtained show that in all the solvents studied the rearrangements occur through a bimolecular reaction pathway involving one molecule of piperidine (k_II). However, depending on the solvent used more catalysed steps contribute to the overall reaction. Thus, in methanol, catalysis (k_MeO) by methoxide ion, derived from the basic ionization of piperidine in methanol, has also been observed and in dioxan or in ethyl acetate, besides the uncatalysed (k_u) and k_II steps, the overall mechanism involves a small contribution from catalysis by two molecules of piperidine (k_III). The results obtained in this work together with those previously obtained in benzene allow exclusion of the addition of piperidine to the C(5)–N(4) bond of the 1,2,4-oxadiazole ring. The k_III step is likely to arise from catalysis of catalysis.