Aqueous oxidation of bisphenol analogues by ozone: Relevance of substituents on reactivity

In recent years, bisphenol A has been progressively replaced by other bisphenol analogues, leading to an increase of their occurrence in aquatic environments. However, limited data is available regarding their removal through oxidation treatments, such as ozonation. In this work, the reactivity of ozone with seven novel bisphenol A substitutes (bisphenol E, bisphenol B, bisphenol AF, bisphenol C, bisphenol AP, bisphenol Z and bisphenol C-Cl) was studied over a wide range of pH by competition kinetics. The second-order rate constants of ozone were determined for their protonated species (k1, k2 and k3), together with their pH-dependent reactivity profile. High and similar reactivity of ozone with all bisphenols was distinguished at basic pH (k3 = 8.83 x 108 - 1.39 x 109 M-1 s-1). This reactivity decreased at neutral pH, although it remained comparable for all bisphenols (kapp = 2 x 106 - 5 x 106 M-1 s-1). In contrast, the even lower reactivity observed at acidic pH exhibited significant variations between them (k1 = 1.54 x 102 - 1.22 x 105 M-1 s-1), due to the influence of the different functional groups, as their behaviour as electron-donating or electron-withdrawing moieties strongly govern their reactivity with ozone. Additionally, the oxidation products resulting from the reaction of ozone with bisphenols at neutral pH were also assessed. The generation of catechol derivatives was suggested as the primary degradation pathway for the majority of bisphenols. Other oxidation products were also commonly detected, such as ortho-quinone derivatives, ring opening products and simple phenolic fragments.