KINETICS AND MECHANISMS OF THE PHOTOLYTIC AND OH-DEGREES RADICAL-INDUCED OXIDATION OF FLUORINATED AROMATIC-COMPOUNDS IN AQUEOUS-SOLUTIONS

Laboratory experiments with H2O2/UV oxidation processes and photolysis at 253.7 nm wavelength have been carried out on dilute aqueous soluti ons (C-0 = 0.1 to 3.0 mM) of trifluorobenzene derivatives (1,3,5-trifl uorobenzene, 1,2,3 and 1,2,4-trifluorobenzene) and of alpha,alpha,alph a-trifluorotoluene in the presence and in the absence of dissolved oxy gen. The analyses of fluoride ions content during the oxidation experi ments showed that the first steps lead to the production of about 2 mo l of F-/mol of trifluorobenzene decomposed and of 1 mol of F-/mol of t rifluorotoluene decomposed. Kinetic studies lead to the determination of the quantum yield for-the photolysis of 1,3,5-trifluorobenzene, 1,2 ,3 and 1,2,4-trifluorobenzene (phi = 0.011, 0.010 and 0.015 respective ly), and of trifluorotoluene (phi = 0.015). The rate constants for the reaction of hydroxyl radicals with these molecules, determined under specific experimental conditions, were found to range from 3.7 10(9) t o 4.9 10(9) M(-1).s(-1)). GC/MS analyses carried out on extracts at di fferent irradiation time (UV, H2O2/UV) lead to the identification of n umerous by-products from trifluorobenzene and trifluorotoluene. They c onsist mostly in hydroxylated and dehalogenated compounds. Dimers have also been observed during photolysis. Moreover, experiments carried o ut under oxygen limiting conditions revealed the formation of other co mpounds. For each case studied, a detailed mechanism involving radical intermediates and the different reaction sequences is proposed.