Kinetic study of the oxidation of phenolic derivatives of alpha,alpha,alpha-trifluorotoluene by singlet molecular oxygen [O2(1delta(g)) and hydrogen phosphate radicals.
The oxidation kinetics and mechanism of the phenolic derivatives of alpha,alpha,alpha-trifluorotoluene, 2-trifluoromethylphenol, 3-trifluoromethylphenol (3-TFMP), 4-trifluoromethylphenol and 3,5-bis(trifluoromethyl)phenol, mediated by singlet molecular oxygen, O2(1delta(g)), and hydrogen phosphate radicals were studied, employing time-resolved O2(1delta(g)) phosphorescence detection, polarographic determination of dissolved oxygen and flash photolysis. All the substrates are highly photo-oxidizable through a O2(1delta(g))-mediated mechanism. The phenols show overall quenching constants for O2(1delta(g)) of the order of 10(6) M(-1) s(-1) in D2O, while the values for the phenoxide ions in water range from 1.2 x 10(8) to 3.6 x 10(8) M(-1) s(-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 photo-oxidation 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(-1) s(-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 singlet molecular oxygen and hydrogen phosphate radicals not only react at different rates with the phenols of alpha,alpha,alpha-trifluorotoluene, but the reactions also proceed through different reaction channels.
Rosso
Janina A
JA
Instituto de Investigaciones Fisicoquímica Teóricas y Aplicadas (INIFTA), Universidad Nacional de La Plata, Casilla de Correo 16, Sucursal 4, (1900) La Plata, Argentina.
Criado
Susana
S
Bertolotti
Sonia G
SG
Allegretti
Patricia E
PE
Furlong
Jorge
J
García
Norman A
NA
Gonzalez
Mónica C
MC
Mártire
Daniel O
DO