The halogenation reactions of 1,3-dihydroxyaromatic compounds and simple methyl ketones in dilute aqueous solution have been investigated in order to elucidate the mechanism of analogous processes involving naturally occurring humic material. The 1,3-dihydroxyaromatic model compounds were most reactive with maximum yields of CHC13 (>90%) and CHBr3 (>70%) at pH 8-10 with substrate concentrations of 10"® M and halogen concentrations of 10"5-10"4 M. At high chlorine concentrations, substantial yields of a variety of Cl-substituted carboxylic acids were detected, whereas at low [Cl2] values, a number of important polyhalogenated reaction intermediates were identified. Halogenation of resorcinol-2-13C produced 13CHC13 and 13CHBr3 with isotopic enrichments equivalent to that of the labeled precursor. The experimental data are generally consistent with a dominant haloform-type reaction mechanism, but some details of these results strongly suggest that several competitive pathways are also involved.

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1,3‐cyclohexanedione‐2‐13C was prepared by intramolecular Claisen condensation of methyl 5‐oxohexanote‐6‐13C with sodium methoxide. Formation of the ketoester starting material involved treatment of a mixed dicarboxylic anhydride with an isotopicallylabelled Grignard reagent, methyl‐13C magnesium iodide. Dehydrogenation of carbon‐13 labelled cyclohexanedione over a palladium/carbon catalyst produced 1,3‐dihydroxybenzene‐2‐13C. Chlorination and bromination of dihydroxybenzene in aqueous solution yielded isotopically‐labelled chloroform and bromoform, each having enriched carbon‐13 contents equivalent to that of the organic substrate.