Investigation on the photoreactions of nitrate and nitrite ions with selected azaarenes in water

The photoreactions of selected azaarenes with nitrate and nitrite ions were investigated under irradiation at lambda=313 nm. The excitation of both an ions leads to several photochemical reactions forming mainly hydroxyl radic als and nitrogen oxides. The purification capability of natural waters i.e. the oxidation of inorganic and organic substances results from the formati on of hydroxyl radicals. Nitrated isomers of azaarenes were found among the main products of the investigated photoreactions. The nitrogen oxides were responsible for the production of nitrated derivatives which possess a hig h toxic potential. Their formation was explained by the parallel occurance of two mechanism, a molecular and a radical one. The molecular mechanism be came more important with increasing ionisation potentials of the azaarenes. The spectrum of oxidized products corresponded to the one got in the photo reactions of azaarenes with hydrogen peroxide. The formation of several oxi dation and nitration products of the pyridine ring with its low electron de nsity was explained by the reaction of excited states of azaarenes. The pho toreactions with nitrite ions only led to the formation of oxidized and nit rated products. Nitroso products were not formed. The reactivity of nitroge n monoxide is too low for its reaction with the azaarenes. (C) 1998 Elsevie r Science Ltd. All rights reserved.