title: The first kinetic evidence for acid catalysis in a monocyclic rearrangement of heterocycles: conversion of the Z-phenylhydrazone of 5-amino-3-benzoyl-1,2,4-oxadiazole into N,5-diphenyl-2H-1,2,3-triazol-4-ylurea.
abstract: The title reaction has been studied in dioxane/water in a large (0.1-14.9) pS+ range, evidencing, together with an uncatalyzed process at intermediate (3.5-8.0) pS+ values, the occurrence of a catalyzed pathway both in the acidic (pS+ 0.1-3.5) and in the basic region (pS+ 8.0-14.9): specific-acid catalysis and general-base catalysis, respectively, have been found to take place by means of kinetic investigations at different buffer concentrations. Mechanisms for the three pathways have been advanced on the grounds of structural features. In a comparison with previous data particular attention has been paid to the acid-catalyzed pathway, herein observed for the first time in an azole-to-azole interconversion. The mechanistic hypotheses seem well supported by ab initio calculations.
authors.affiliation: Dipartimento di Chimica Organica "A. Mangini", Università di Bologna, Via S. Donato 15, I-40127 Bologna, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Cosimelli
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Frenna
authors.forename: Susanna
authors.initials: S
authors.lastname: Guernelli
authors.forename: Camilla Zaira
authors.initials: CZ
authors.lastname: Lanza
authors.forename: Gabriella
authors.initials: G
authors.lastname: Macaluso
authors.forename: Giovanni
authors.initials: G
authors.lastname: Petrillo
authors.forename: Domenico
authors.initials: D
authors.lastname: Spinelli