Kinetic Study of the Reactions of Singlet Molecular Oxygen [O2(1īg)] and Hydrogen Phosphate Radicals with Phenolic Derivatives of Ą, Ą, Ą- Trifluorotoluene

J. A. ROSSO; S. CRIADO; S. G. BERTOLOTTI; P. ALLEGRETTI; J. FURLONG; N. A. GARCÍA; M. C. GONZALEZ; D. O. MÁRTIRE

Photochemical and Photobiological Sciences

ROYAL SOC CHEMISTRY

Año: 2003 p. 882 - 887

1474-905X

The oxidation kinetics and mechanism of the phenolic derivatives of α,α,α-trifluorotoluene, 2-trifluoromethylphenol, 3-trifluoromethylphenol (3-TFMP), 4-trifluoromethylphenol and 3,5-bis(trifluoromethyl)phenol, mediated by singlet molecular oxygen, O2(1∆g), and hydrogen phosphate radicals were studied, employing time-resolved O2(1∆g) phosphorescence detection, polarographic determination of dissolved oxygen and flash photolysis. All the substrates are highly photo-oxidizable through a O2(1∆g)-mediated mechanism. The phenols show overall quenching constants for O2(1∆g) of the order of 106 M1 s1 in D2O, while the values for the phenoxide ions in water range from 1.2 × 108α,α,α-trifluorotoluene, 2-trifluoromethylphenol, 3-trifluoromethylphenol (3-TFMP), 4-trifluoromethylphenol and 3,5-bis(trifluoromethyl)phenol, mediated by singlet molecular oxygen, O2(1∆g), and hydrogen phosphate radicals were studied, employing time-resolved O2(1∆g) phosphorescence detection, polarographic determination of dissolved oxygen and flash photolysis. All the substrates are highly photo-oxidizable through a O2(1∆g)-mediated mechanism. The phenols show overall quenching constants for O2(1∆g) of the order of 106 M1 s1 in D2O, while the values for the phenoxide ions in water range from 1.2 × 108fluoromethylphenol (3-TFMP), 4-trifluoromethylphenol and 3,5-bis(trifluoromethyl)phenol, mediated by singlet molecular oxygen, O2(1∆g), and hydrogen phosphate radicals were studied, employing time-resolved O2(1∆g) phosphorescence detection, polarographic determination of dissolved oxygen and flash photolysis. All the substrates are highly photo-oxidizable through a O2(1∆g)-mediated mechanism. The phenols show overall quenching constants for O2(1∆g) of the order of 106 M1 s1 in D2O, while the values for the phenoxide ions in water range from 1.2 × 1082(1∆g), and hydrogen phosphate radicals were studied, employing time-resolved O2(1∆g) phosphorescence detection, polarographic determination of dissolved oxygen and flash photolysis. All the substrates are highly photo-oxidizable through a O2(1∆g)-mediated mechanism. The phenols show overall quenching constants for O2(1∆g) of the order of 106 M1 s1 in D2O, while the values for the phenoxide ions in water range from 1.2 × 108flash photolysis. All the substrates are highly photo-oxidizable through a O2(1∆g)-mediated mechanism. The phenols show overall quenching constants for O2(1∆g) of the order of 106 M1 s1 in D2O, while the values for the phenoxide ions in water range from 1.2 × 1082(1∆g)-mediated mechanism. The phenols show overall quenching constants for O2(1∆g) of the order of 106 M1 s1 in D2O, while the values for the phenoxide ions in water range from 1.2 × 1082(1∆g) of the order of 106 M1 s1 in D2O, while the values for the phenoxide ions in water range from 1.2 × 108 to 3.6 × 108 M1 s1. 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 HPO48 M1 s1. 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 HPO4fluoromethyl-1,4-benzoquinone is suspected to be the main photooxidation product for the substrate 3-TFMP. The absolute rate constants for the reactions of HPO44 with the substrates range from 4 × 108 to 1 × 109 M1 s1. The 3-trifluoromethylphenoxyl radical was observed as the organic intermediate formed after reaction of 3-TFMP with HPO4 with the substrates range from 4 × 108 to 1 × 109 M1 s1. The 3-trifluoromethylphenoxyl radical was observed as the organic intermediate formed after reaction of 3-TFMP with HPO48 to 1 × 109 M1 s1. The 3-trifluoromethylphenoxyl radical was observed as the organic intermediate formed after reaction of 3-TFMP with HPO44 , yielding 2,2-bis(fluorohydroxymethyl)biphenyl-4,4- diol as the end product. The observed results indicate that singlet molecular oxygen and hydrogen phosphate radicals not only react at different rates with the phenols of α,α,α-trifluorotoluene, but the reactions also proceed through different reaction channels., yielding 2,2-bis(fluorohydroxymethyl)biphenyl-4,4- diol as the end product. The observed results indicate that singlet molecular oxygen and hydrogen phosphate radicals not only react at different rates with the phenols of α,α,α-trifluorotoluene, but the reactions also proceed through different reaction channels.fferent rates with the phenols of α,α,α-trifluorotoluene, but the reactions also proceed through different reaction channels.fferent reaction channels.