Photochemically induced nitration and hydroxylation of organic aromatic compounds in the presence of nitrate or nitrite in ice.
|Název česky||Fotochemicky indukovaná nitrace a hydroxylace aromatických organických sloučenin v přítomnosti dusičnanů a dusitanů v ledu.|
|Druh||Článek v odborném periodiku|
|Časopis / Zdroj||Journal of Photochemistry and Photobiology A: Chemistry|
|Fakulta / Pracoviště MU|
|Klíčová slova||Photochemistry; Ice; Snow; Nitrate; Nitrite; Aromatic compounds; Phenol; Nitration; Oxidation.|
|Popis||The photochemistry of three model aromatic compounds (phenol, anisole, and 4 methoxyphenol; c = 0.001 mol/L) in frozen aqueous solutions containing sodium nitrite or nitrate (from c = 0.01 to 0.1 mol/L) at minus 15 C was investigated. Nitration, hydroxylation, and coupling reactions were found to be the principal chemical processes, presumably taking place in the quasi-liquid layer covering the ice crystal surfaces where both hydrophobic organic and water soluble inorganic compounds were accumulated prior to irradiation. While primary photoproducts were identified at low reaction conversions, exhaustive (quartz or Pyrex filtered) UV irradiation produced a very complex mixture of secondary photoproducts. The photoreactions proceeded predominantly by the nitrite or nitrate photoexcitation but chemistry of the excited organic chromophores was also observed. Phenol and 4 methoxyphenol photolysis afforded the corresponding nitro and hydroxycompounds, as well as biphenyl and diphenylether derivatives. The presence of nitrite or nitrate caused that qualitatively the same photoproducts were produced; therefore both were the source of the NOx or HO radicals. In contrast, irradiation of anisole under the same reaction conditions afforded phenol nearly exclusively. It is demonstrated that the OH group of phenols played an important role in the course of hydroxylation and nitration reactions. The results from this study may support assumptions according to which photolysis of nitrate in the snowpack is responsible for oxidation of organic precursors to their hydroxy or carbonyl derivatives.|