Kinetic study of the oxidation of phenolic derivatives of Alfa,Alfa,Alfa- trifluorotoluene by singlet molecular oxygen [O2(1g)] and hydrogen phosphate radicals.

Producción CyT

Artículo

Autoría

CRIADO, SUSANA NOEMI

Fecha

2003

Editorial y Lugar de Edición

RSC Publishing

Revista

Photochemical and Photobiological Sciences, vol. 2 (pp. 882-887) RSC Publishing

Resumen Información suministrada por el agente en SIGEVA

The oxidation kinetics and mechanism of the phenolic derivatives of a,a,a-trifluorotolueno, 2-trifluoromethylphenol, 3-trifluoromethylphenol, (3-TFMP), 4-trifluoromethylphenol and 3,5-bis (trifluoromethyl)phenol, mediated by singlet molecular oxygen, O2(1Dg), and hydrogen phosphate radicals were studied, employing time-resolved O2(1Dg) phosphorescence detection, polarographic determination of dissolved oxygen and flash photolysis. All the substrates are highly photo-oxidizable through a O2(1Dg)... The oxidation kinetics and mechanism of the phenolic derivatives of a,a,a-trifluorotolueno, 2-trifluoromethylphenol, 3-trifluoromethylphenol, (3-TFMP), 4-trifluoromethylphenol and 3,5-bis (trifluoromethyl)phenol, mediated by singlet molecular oxygen, O2(1Dg), and hydrogen phosphate radicals were studied, employing time-resolved O2(1Dg) phosphorescence detection, polarographic determination of dissolved oxygen and flash photolysis. All the substrates are highly photo-oxidizable through a O2(1Dg)-mediated mechanism. The phenols show overall quenching constants for O2(1Dg) of the order of 10 6 M-1s-1 in D2O, while the values for the phenoxide ions in water range from 1.2 x 10 8 to 3.6 x 108 M-1s-1. The effects of the pH and polarity of the medium on the kinetics of the photo-oxidative process suggest a charge-transfer mechanism. 2-Trifluoromethyl-1,4-benzoquinone is suspected to be the main photooxidation product for the substrate 3-TFMP. The absolute rate constants for the reactions of HPO4.- with the substrates range from 4 x 10 8 to 1 x 10 9 M-1s-1. The 3-trifluoromethylphenoxyl radical was observed as the organic intermediate formed after reaction of 3-TFMP with HPO4.-, yielding 2,2’-bis (fluorohydroxymethyl)biphenyl-4,4’-diol as the end product. The observed results indicate that the singlet molecular oxygen and hydrogen phosphate radicals not only react at different rates with the phenols a,a,a-trifluorotolueno, but the reactions also proceed through different reaction channels

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Palabras Clave

SINGLET MOLECULAR OXYGENPHENOLIC COMPOUNDSPHOSPHATE RADICALSOXIDATION