Ionic dissociation of 4-substituted 2,6-dimethylphenols

Abstract

The pK values of 4-X-2,6-dimethylphenols (X = Me, MeO, H, F, Br, MeCO, CN, CHO, NO2, and NO) have been measured in water, at 25°, by potentiometric titration. For dissociation of 2,6-dimethylphenols, ρ is 21% larger than the value for phenols, and this is attributed to steric inhibition of solvation in the 2,6-dimethylphenoxide anions. The pK value of 4-nitroso-2,6-dimethylphenol suggests that it exists in aqueous solution as the monoxime of 2,6-dimethylbenzoquinone.