Stability of aryl azides

Many molecules with a high nitrogen content are potentially explosive. Low molecular weight aryl azides are generally stable but as undiluted solids or liquids they should be handled with respect, especially if they are prepared in gram amounts. For example, distillations should be done under 

It was concluded that dithiols should not be used in photoaffinity labeling experiments with aryl azides and monothiols should be used with caution. The reduction reaction can often be monitored spectrophotome-trically, e.g. 2-nitro-4-azidoanilines which are red-orange (Xmax 480 nm in H20) are converted to purple diamines (Xmax 550 nm). TLC and IR spectroscopy are also useful (Staros et al., 1978). 

Obviously the investigator should also be aware of any ground state reactions peculiar to the system under study. For example 2-azidopyridines isomerize to tetrazoles which are usually less sensitive than the azide to irradiation (Fig. 3.1). The position of the equilibrium is both temperature, solvent and pH dependent. Even if the equilibrium constant for such an isomerization in solution is known the situation in a ligand binding site cannot be predicted. Azide-tetrazole isomerization was an important consideration in experiments using 2-azidoadenine derivatives which have recently been described by MacFarlane et al. (1982). 

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