Comparative studies on the oxidative dechlorination of chlorophenols by a superoxide complex

Abstract

The chlorophenols (CPs), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP), are potent environmental hazards. They can be dechlorinated to safer products by reacting them with the Co(III)-bound superoxo complex [(NH3)5Co(µ-O2)Co(NH3)5]5+ (1). In acidic media, the redox reactions between 1 and all three CPs follow a first-order process and the observed rate constant ko values increase with increasing concentrations of CPs and pH of the medium. Our observations suggest that the deprotonated forms of the CPs are ~ 105 times more reactive than the protonated forms, and the reactions proceed via a common free radical mechanism. Initially, the CP molecules undergo 2-e− oxidations by complex 1 to generate phenolic radicals, which then form unstable quinones. Through the aromatic ring opening, the latter intermediates finally degrade to different products. The reactivity order for these CPs is 4-CP ≈ 2,4,6-TCP > 2,4-DCP.