Reactivity of mucohalic acids in water.

One group of disinfection byproducts of increasing interest are the halogenated furanones, which are formed in the chlorination of drinking water. Among these halofuranones is mucochloric acid (MCA, 3,4-dichloro-5-hydroxyfuran-2(5H)-one), and mucobromic acid (MBA, 3,4-dibromo-5-hydroxyfuran-2(5H)-one). Both mucohalic acids (MXA) are direct genotoxins and potential carcinogens, with the capacity to alkylate the DNA bases guanosine, adenosine and cytosine, and they have been measured in concentrations ranging up to 700 ng/l in tap water. MCA and MBA react in basic aqueous medium to form mucoxyhalic acids (4-halo-3,5-hydroxyfuran-2(5H)-one). Since: i) this reaction may represent the first step in the abiotic decomposition of mucohalic acids, ii) mucoxyhalic acids have been proposed as possible intermediates in the reaction of MXA with DNA, a kinetic study of the reaction mechanism is of interest. Here, the following conclusions were drawn: a) At moderately basic pH, the reaction of mucohalic acids with OH(-) to form mucoxyhalic acids is kinetically significant. b) The nucleophilic attack of hydroxide ions on MXA occurs through a combination of two paths: one of them is first-order in hydroxide whereas the other is second-order and are proposed to occur through the deprotonation of the hydrate of MXA. c) The hydration constants of mucohalic acids -0.23 and 0.17 for MCA and MBA respectively - corresponds to the very significant hydrate concentrations. Since hydrates are not electrophilic, these values imply a decrease in the alkylating capacity of mucohalic acids.