Oxidation of phenyl trifluoromethyl sulphide: A pulse radiolysis and theoretical study

Pulse radiolysis technique and quantum chemical calculations have been employed to study the pH dependent reaction of the OH radical with phenyl trifluoro methyl sulphide (PTFMS). The transient absorption spectrum in neutral conditions with maximum at 330–340 nm (ɛ340 = 2750 dm3(mol cm)−1) consisted of the OH addition product and its yield decreased at pH 1 with 15% OH contributing to the formation of the monomeric sulphur radical cation. The yield and the lifetime of the radical cation were observed to increase with acid concentration reaching 100% at 6.8 mol dm−3 HClO4 with molar absorptivity values of 11,500 and 6150 dm3(mol cm)−1 at 320 and 560 nm respectively. Quantum chemical studies at MP2 level with PTFMS and phenyl methyl sulphide (PMS) revealed that the OH radical adds to the aromatic ring and not to S atom. The para OH adduct of PTFMS is the most stable (binding energy = 22.41 kcal mol−1) whereas the ipso addition product is less stable (5.10 kcal mol−1). The optimized geometries of PMS and PTFMS monomeric sulphur radical cations have shown the charge distribution mostly on the S atom in the former but was extended to the aromatic ring in the latter. Neither the oxidation of PTFMS by pulse radiolysis (Cl2−, Br2− or SO4−) nor by cyclic voltammetry was observed.