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

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 k_o 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. [ABSTRACT FROM AUTHOR]