Photoassisted dehalogenation and mineralization of chloro/fluoro-benzoic acid derivatives in aqueous media

The photoassisted dehalogenation and mineralization of chloro/fluoro-benzoic acid derivatives occurring at the TiO2/H2O interface under oxygen-saturated and UV-light exposure were examined by UV absorption spectroscopy, ion chromatography and time-of-flight (TOF) mass spectrometry to identify intermediate products. Contrary to defluorination, dechlorination occurred readily, presumably because of the weaker CCl bond relative to the CF bond. Photodegradation through aromatic ring cleavage also occurred fairly rapidly followed by the ultimate evolution of CO2 gas through prior formation of formate and bicarbonate species. When negative inductive effect groups, such as the chloro and fluoro groups, are positioned ortho and para to the carboxylic acid group, as in the 2Cl–4F–BA, 2Cl–6F–BA, and 4Cl–2F–BA derivatives, dechlorination was faster than when the chloro group was meta to the carboxylic acid group. Theoretically calculated frontier election densities and point charges of all the atoms in the Cl/F–BA derivatives are given. Plausible steps in the photo-degradation/-mineralization of these substrates are discussed.