Collect. Czech. Chem. Commun. 1985, 50, 2722-2729

Cyclization of O-benzoylbenzamidoxime derivatives in water-alcohol media

František Grambal and Jan Lasovský

Department of Inorganic and Physical Chemistry, Palacký University, 772 00 Olomouc


O-Benzoylated benzamidoximes give 1,2,4-oxadiazoles (yields above 90%) in water-alcoholic media of pH = 2.45 to 6.20. The cyclization rate has been studied with 28 derivatives containing different substituents. The reaction is accelerated by electron-donor substituents at 4-position of benzamidoxime and by electron-acceptor substituents at 4'-position of benzoyl. The dependence of the rate constants vs σ values of the substituents fulfils the two-parameter Hammett equation at a 99% probability level. The activation parameters have been determined, and effects of polarity of medium, kinetic isotopic effect, and the reaction mechanism are discussed.