Decomposition of tetrachloro-1,4-benzoquinone (p-Chloranil) in aqueous solution

Article abstract of DOI:10.1021/es00011a006

p-Chloranil (2,3,5,6-tetrachloro-2,5-cyclohexadiene-1,4-dione; tetrachloro-1,4-benzoquinone) has been observed as an oxidation product in processes used to oxidize pentachlorophenol (PCP), has known biocidal properties, and has been implicated in genotoxic effects associated with PCP. Chloranil undergoes displacement of chloride by hydroxide under highly alkaline conditions, but no previous work on chloranil decomposition has been conducted at environmentally relevant pH. Electrospray mass spectrometry was used in this study to confirm the two-step hydrolysis of chloranil to yield chloranilic acid (2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone), and the kinetics of each step were quantified as a function of pH. The half-life of chloranil at pH 7 is estimated to be slightly over 1 h, while that of its first hydrolysis product (trichlorohydroxyquinone) is about 21 d, Chloranil also reacts with hydrogen peroxide in a pH-dependent manner at rates substantially greater than the rate of spontaneous hydrolysis. The low yield of chloranilic acid from this reaction suggests that other, as yet unidentified, products are formed. Chloranilic acid has lower acute toxicity (BS measured in the Microtox screening assay) than does chloranil, so that promoting the accelerated hydrolysis of chloranil may be advantageous in waste treatment or remediation processes in which it is formed.