title: Photodegradation mechanisms of 1-nitropyrene, an environmental pollutant: the effect of organic solvents, water, oxygen, phenols, and polycyclic aromatics on the destruction and product yields.
abstract: This work describes studies of the photodegradation mechanism of 1-nitropyrene (1-NO(2)Py) in a chemical model system consisting of an organic solvent and known constituents of an aerosol particle. Photoproducts such as 1-hydroxypyrene (1-OHPy), 1-hydroxy-x-nitropyrenes (1-OH-x-NO(2)Py), 1-nitrosopyrene, and 1,6- and 1,8-pyrenediones were identified by high-performance liquid chromatography (HPLC) and HPLC/mass spectrometry (HPLC/MS) techniques, and their quantum yields show a significant dependence on the type of solvent. The photodegradation quantum yield of 1-NO(2)Py, φ((-1-NO2Py)), was larger in toluene, benzene, and polar protic solvents (10(-3)) in comparison with nonpolar and polar aprotic solvents, where the yield is on the order of 10(-4). In solvents with an abstractable hydrogen atom, the products formed in higher yields were 1-OHPy and 1-OH-x-NO(2)Py. These represent 60-80% of the photodestruction yield and result from abstraction and recombination reactions of the pyrenoxy radical, an intermediate postulated to be formed as a result of a nitro-nitrite rearrangement in nitroaromatics. The small O(2) effect in the photodegradation yield and the quenching experiments with azulene demonstrate the small contribution of the (3)(π,π*) state in the 1-NO(2)Py photoreaction. The nitrosopyrene product was not observed under these conditions, demonstrating the participation of the (3)(π,π*) state in its formation. In the presence various phenol aerosol constituents, the photodegradation yield increased by 10-fold in all solvents. This effect is partly ascribed to the reaction of the (3)(π,π*) state with the phenol. The effect of water resulted in the reduction of the 1-NO(2)Py photodegradation yield and of its photoproducts. The phototodegradation of 1-NO(2)Py was also studied in a viscous solvent, hexadecane, and it was determined that this medium does not inhibit its photodecay.
authors.affiliation: Department of Chemistry, University of Puerto Rico, Río Piedras Campus, San Juan, Puerto Rico, 00931-3346.
authors.forename: Zulma I
authors.initials: ZI
authors.lastname: García-Berríos
authors.forename: Rafael
authors.initials: R
authors.lastname: Arce
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004785:Environmental Pollutants / Q000737:chemistry*; D013058:Mass Spectrometry; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D010782:Photolysis; D011721:Pyrenes / Q000737:chemistry*; D011789:Quantum Theory; D012997:Solvents; D013696:Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry*
chemical_list: D004785:Environmental Pollutants; D010636:Phenols; D011721:Pyrenes; D012997:Solvents; D014867:Water; C044707:1-nitrosopyrene; C031174:1,6-pyrenequinone; C033146:1-hydroxypyrene; C031175:1,8-pyrenequinone; D010100:Oxygen; C032668:1-nitropyrene