Effect of dimethyl sulfoxide and dimethylformamide on the stability of 4-halo-8-quinolinols

Polyhalo-8-quinolinols with chlorine or bromine in position 4 were not stable in DMSO or DMF. The degradation product from 4,5-dichloro-8-quinolinol was 5-chloro-4,8-quinolindiol and the major product from 4,5-dibromo-8-quinolinol was 3,5-dibromo-4,8-quinolindiol. 4,5,7-Trichloro- and 4,5,7-tribromo-8-quinolinols yielded similar hydrolytic products, and for the bromo compound, a rebrominated product in DMSO. In DMF rebromination did not occur. In pyridine-d(5) these reactions did not take place, indicating a special ability of DMSO and DMF to cause such hydrolysis at position 4 of 4-halo-8-quinolinols.