Determination of ionization constants of nitro-,dinitro hydroxyphenylphthalides & related 2,6-dinitro-4-substituted phenols

Abstract

The ionization constants of 2,6-dinitro-4-methylphenol, 2,6-dinitro- 4-<i>t</i>-butylphenol, 3-(3-nitro-4-hydroxyphenyl)phthalide and 3-(3,5- dinitro-4-hydroxyphenyl)phthalide have been determined. The 3- (3-nitro-4-hydroxyphenyl)phthaJide is found to be weaker acid than <i>o</i>-nitrophenol, whereas 3-(3,5-dinitro-4-hydroxyphenyl) phthalide is a stronger acid than 2,6-dinitrophenol. The strength of acidity of phthalides is most probably affected by steric effect between the charged oxygen of the nitro group and that of lactonic moiety and to the size of solvation sphere of the phenoxide ion.