Pyrolysis of Aryl Azides.X. Effects of Azide Concentration on Rate Constants and Product Yields

Abstract

First-order rate constants (k₁) have been measured for pyrolysis of azidobenzenes in decalin solution, in the presence of a free-radical chain inhibitor to prevent any induced decomposition. The new values of k₁ for the spontaneous unimolecular thermolysis are lower than previously reported ones, and require revision of published neighbouring group effects. Product yields ( azo compound and primary amine) vary with initial concentration of azide in ways which suggest the species responsible for induced decomposition is not triplet arylnitrene , but a solvent-derived free radical. There is no evidence for induced decomposition when nitrobenzene is the solvent.

For aryl azides with no neighbouring group effects operating in their pyrolysis, the Arrhenius parameters E_act and ΔS_actobey a precise linear relationship.