Science and Technology Production
Article
Authorship
Date
1998
Magazine
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY,
vol. 119
(pp. 9-14)
Summary
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SIGEVA
The kinetics of the dye-sensitized photooxygenation of the monohydroxylated N-heteroaromatic compounds, 2-hydroxypyridine, 3- hydroxypyridine, 4-hydroxypyridine, 4-hydroxyquinoline, 8-hydroxyquinoline, 2-hydroxypyrimidine and 4-hydroxypyrimidine, with the basic structures of some pesticides, has been studied. Rate constants in the range 106-108 M-1 s-1 for both the overall and the reactive singlet molecular oxygen [O2(1Dg)] quenching were determined by time-resolved O2(1Dg) phosphorescence dete...
The kinetics of the dye-sensitized photooxygenation of the monohydroxylated N-heteroaromatic compounds, 2-hydroxypyridine, 3- hydroxypyridine, 4-hydroxypyridine, 4-hydroxyquinoline, 8-hydroxyquinoline, 2-hydroxypyrimidine and 4-hydroxypyrimidine, with the basic structures of some pesticides, has been studied. Rate constants in the range 106-108 M-1 s-1 for both the overall and the reactive singlet molecular oxygen [O2(1Dg)] quenching were determined by time-resolved O2(1Dg) phosphorescence detection and polarographic methods. Photooxidation quantum yields were in the range of 0.01-0.50 in the cases where reaction was observed, with values significantly higher in aqueous media. The hydroxy substituent plays a key role in the photooxidative process. In 2- and 4-hydroxypyridines, 4-hydroxyquinoline and 4-hydroxypyrimidines the predominant, and almost exclusive, presence of the tautomeric oxo form drastically suppresses the interaction with O2(1Dg). In the case of 3-hydroxypyridine and 8-hydroxyquinoline, compounds with hydroxy form, the OH-ionization greatly enhances the photooxidative process. Experimental evidence suggests the participation of a charge-transfer mediated mechanism, involving an initial excited encounter complex.
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