Abstract |
The use of prechlorination in drinking water treatment results in contact of free chlorine with activated carbon which has been added to remove organic compounds from water. The chlorine then reacts with the carbon and adsorbed compounds. Free chlorine reacts readily with a group of phenolic compounds (phenol, guaiacol, catechol, 2,6-dimethoxyphenol, and p-chlorophenol) in dilute aqueous solutions (.00001 M) to produce mono-, di-, or trichloro derivatives, but when it reacts with phenols adsorbed on granular activated carbon (GAC), many additional products are formed. GAC exposed to chlorine becomes capable of promoting reactions such as hydroxylation of the aromatic ring, oxidation to quinones, chlorine substitution, carboxylation, and oxidative coupling (dimer formation). The formation of chloro-hydroxybiphenyls (hydroxylated PCBs) (in vivo metabolites of PCBs) is particularly important because of their potential toxicity. Such compounds are the main reaction products from chlorophenols, but they are also formed in smaller amounts from nonchlorinated phenols (phenol and guaiacol). (Copyright (c) 1985, American Chemical Society.) |