Producción CyT
Artículo
Autoría
Fecha
2000
Revista
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY,
vol. 135
(pp. 207-212)
Resumen
Información suministrada por el agente en
SIGEVA
The kinetics of the dye-sensitized photooxidation of 2-amino-4-hydroxy-6-methyl-pyrimidine (AHMPD), a compound with the basic molecular structure of some systemic pyrimidine fungicides, has been studied in solution in water and in the mixture acetonitrile-water 4:1 v/v. Rate constants in the range 9 x 104-2.7 x 107 M-1 s-1 for both the overall and the reactive singlet molecular oxygen [O2(1Dg)] quenching processes were determined by time-resolved O2(1Dg)-phosphorescence detection and polarograp...
The kinetics of the dye-sensitized photooxidation of 2-amino-4-hydroxy-6-methyl-pyrimidine (AHMPD), a compound with the basic molecular structure of some systemic pyrimidine fungicides, has been studied in solution in water and in the mixture acetonitrile-water 4:1 v/v. Rate constants in the range 9 x 104-2.7 x 107 M-1 s-1 for both the overall and the reactive singlet molecular oxygen [O2(1Dg)] quenching processes were determined by time-resolved O2(1Dg)-phosphorescence detection and polarographic methods. Photooxidation quantum yields were in the range 0.005-0.41, with values significantly higher in alkalinized media. On the contrary, pyrimidine, 2-aminopyrimidine, 4-hydroxypyrimidin and 6-methylpyrimidine do not react with O2(1Dg), in neutral or alkalinized D2O solutions. The presence of a 4-hydroxy group in pyrimidines plays a key role in the photooxidative process, because the formation of the tautomeric 4-oxo form, the predominant one in aqueous solution, diminishes or suppresses the interaction with O2(1Dg). However, in the presence of alkali the OH-ionization greatly enhances the photooxidation. The experimental evidence suggests a charge-transfer mediated mechanism involving an initial encounter excited complex. These results also show that the sensitized photooxidation is an alternative pathway for the environmental or programmed degradation of these colorless N-heteroaromatic compounds, in special in OH-ionized form.
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