The reported pH for the precipitation of the quinoline acid ( ) is Congo red (pH 5), which upon decarboxylation and chlorination affords 4,7-dichloroquinoline ( ) with 3-4% of the 4,5dichloroquinoline isomer (12). In this study, we envisaged that, owing to the difference in acidity, the two isomers, or at least the majority thereof, would precipitate at different pH values, and thus be isolable (Figure ). Upon hydrolysis of 9 with NaOH, the resulting mixture is basified to pH 8.2-8.4, instead of pH 4 as reported in the literature. The precipitate is then isolated by filtration and slurry-washed at pH 4 to remove any remaining sodium salt. The resulting quinoline acid is then subjected to decarboxylation and chlorination with POCl3 to afford the target product 4,7-dichloroquinoline ( ) in high purity. We began our investigation by precipitating the quinoline acid (10) at pH 6.5, which afforded the acid in almost quantitative yields (98%, Table , Entry 1). However, GC assay results indicated that the final product is contaminated with the isomer (Figure ).