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The equilibrium constant in dioxane between azido and tétrazole isomers has been obtained for five heterocyclic azides (2-azido thiazoles, benzothiazole, benzoxazole, and 3-azido isoxazole) by proton nmr and dipole moment- studies. The last method involves a comparison between experimental and calculated (INDO, CNDO/2, CNDO/S) dipole moments. The CNDO/S method gives the best equilibrium constants and entropy factor (ΔS ∼ 50 J K−1 mol−1). A value of 114° for the C—N—N angle is found to account satisfactorily for certain properties (energy, dipole moment, photoelectron spectra) of aromatic azides. The heterocyclic azidoimines prefer the Z conformation.

The reaction of a reducing agent with a transition-metal salt provides a good method for obtaining hydrogenation catalysts. The reducing agent may be a metal with an oxidation potential lower than of the transition metal,1-7 a hydride such as LiAlH4,8 NaBH4,9-1l and SiHR3,12,13 or the associations NaH-t-BuOH14 or NaH-t-AmOH.15The purpose of this work is to study the reduction, in organic media, of nickel halide with low-oxidation-potential metals. This procedure allows one to obtain a finely divided pure metal, exhibiting, in general, catalytic activity greater than commercial Raney nickel.