PHOTOOXIDATION OF ORGANIC AND INORGANIC SUBSTRATES DURING UV PHOTOLYSIS OF NITRITE ANION IN AQUEOUS-SOLUTION

The UV photolysis (360 nm) of nitrite anion has been investigated in aqueous solution in the presence of organic and inorganic substrates: alcohols, 1,4-dioxane, sodium ascorbate, Me2CO, Me2SO, HCOONa, NaSCN, NaN3, Na2S, and Na2SO3. The hydroxyl radical, the primary photodissociation product of NO2-, was observed by electron spin resonance (EPR) using the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO). With nitromethane (NM) in alkaline solution as a spin trapping agent, we observed NO2. which is a product of HO. self-scavenging by nitrite. In the presence of organic/inorganic substrates, the HO. radical gives rise to secondary radicals which we trapped and identified as DMPO or NM adducts; the respective EPR spectra are presented. Secondary carbon radicals react with oxygen in solution increasing the yield of oxygen consumption 10-1000 times over the control level. The quantum yield of O2 consumption increases with increasing molar ratio of the substrate/NO2-, usually following the plot of oxygen solubility in solution. Besides HO. radicals, nitrogen oxides and inorganic nitrogen peroxides may also contribute to oxidation by nitrite. We also detected weak singlet oxygen phosphorescence during UV irradiation of NO2- in deuterium oxide.