Aqueous atmospheric chemistry: formation of 2,4-dinitrophenol upon nitration of 2-nitrophenol and 4-nitrophenol in solution.
Field studies have shown that the powerful phytotoxic agent 2,4-dinitrophenol is very likely to form in the atmospheric aqueous phase upon nitration of 2-nitrophenol or 4-nitrophenol. However, until now, the nitration pathway and the relative importance of the two mononitrophenols as sources of 2,4-dinitrophenol were not known. The present study shows that 2,4-dinitrophenol formation from mononitrophenols can take place upon photolysis and photooxidation of nitrite/nitrous acid (NO2-/HONO) and that nitrogen dioxide plays a key role in the process. A possible pathway might be the reaction between light-excited mononitrophenols (both 2- and 4-isomers) and nitrogen dioxide, in the presence of oxygen. As an alternative, nitration might involve *NO3 + *NO2. Possible sources of nitrogen dioxide in the atmospheric aqueous phase are dissolution from the gas phase and oxidation of NO2-. In the latter case, however, it is necessary that NO2- oxidation is faster than the oxidation of mononitrophenols. This would happen, for instance, in the presence of hematite under irradiation. Radiation absorption and scattering by hematite would also inhibit the direct photolysis of nitrophenols. The formation rate and the yield of 2,4-dinitrophenol are slightly higher when starting from 2-nitrophenol than those from 4-nitrophenol, but they are compensated by the higher concentration of 4-nitrophenol in the atmospheric aqueous phase.
Vione
Davide
D
Dipartimento di Chimica Analitica, Universita di Torino, Via Pietro Giuria 5, 10125 Torino, Italy. davide.vione@unito.it
Maurino
Valter
V
Minero
Claudio
C
Pelizzetti
Ezio
E
D019297:2,4-Dinitrophenol / Q000138:chemical synthesis*; D001272:Atmosphere / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D009585:Nitrogen Dioxide / Q000737:chemistry; D009596:Nitrophenols / Q000737:chemistry; D010782:Photolysis; D011891:Rain / Q000737:chemistry*; D014466:Ultraviolet Rays
D009596:Nitrophenols; C045573:2-nitrophenol; D019297:2,4-Dinitrophenol; D009585:Nitrogen Dioxide; C024836:4-nitrophenol