A Photoelectron Spectroscopic Study of the 2-Azidopyridine ⇋ Tetrazolo [1.5-α]Pyridine Equilibrium between 391 and 533 K

The azido/tetrazole equilibrium has been widely examined1,2,3 but most of the studies concern the solid state and the solution. The publications dealing with the vapour phase are rare and contain only qualitative information obtained either by IR or MS. However, it is clearly established that the azido form is stabilized at high temperatures. In the particular case of 2-azidopyridine I, according to 1H NMR and IR data, the equilibrium lies strongly on the side of the tetrazole II in solution.3,4 In the vapour phase at high temperature, mass spectrometry,5 IR,6 and the nature of compounds obtained by gas phase pyrolysis7,8 of tetrazolo [1,5-α]pyridines, shown that the azide form is favoured in those conditions.