The photochemistry of an aryl pentazole in liquid solutions: The anionic 4-oxidophenylpentazole (OPP)

Abstract This paper reports a study on the photolysis of an aryl pentazole in solution. 4-Oxidophenylpentazole (OPP) was irradiated in water and in acetonitrile at its first absorption band (320 and 370 nm, respectively) and at 193 nm. 4-Oxidophenylazide (OPA) was also investigated under similar conditions for comparison. NMR and UV–vis absorption spectroscopies of the products show that the major stable products of OPP photolysis in acetonitrile are OPA (which is also a thermal product), 4,4′-dihydroxyazobenzene, and 4-aminophenol while in water the main products are OPA and indophenol. The final product distribution obtained upon 193 nm irradiation is essentially the same as that found for the longer wavelength sources used. In these experiments some of the products are formed upon cleavage of the CN bond connecting the phenyl and the pentazole rings. These reactions are due to secondary collisional processes and not to a primary photochemical event. A mechanism accounting for the results is proposed.