Kinetic Evidence for the Formation of Azene (Electron-deficient Nitrogen) Intermediates from Aryl Azides

Abstract

The kinetics of the thermal decomposition of a group of phenyl and 2-biphenylyl azides bearing halogen, nitro, methyl or methoxy substituents have been measured at several temperatures and in different solvents. The variation of rate with substitution is small; the enthalpies and entropies of activation show a linear relation. None of these functions can be correlated satisfactorily by the Hammett equation; M-substituents have little effect on the activation enthalpies, but psubstituents have an effect that follows the order of the values of Δ (= σp - σm). There is little effect of solvent on the rates other than a weak acceleration, by hydroxylic solvents. The over-all behavior is best accounted for by initial cleavage to an aryl azene intermediate, Ar-N:. © 1962, American Chemical Society. All rights reserved.