POTENTIOMETRIC DETERMINATION OF THE APPARENT DISSOCIATION-CONSTANTS OF SOME DICARBOXYLIC-ACIDS IN VARIOUS HYDROORGANIC MEDIA

The apparent dissociation constants of malic acid (hydroxybutanedioic acid), tartaric acid (2,3-dihydroxybutanedioic acid), phthalic acid (1 ,2-benzenedicarboxylic acid), and succinic acid (butane-1,4-dioic acid ) were determined at 25 degrees C and ionic strength I - 0.10 mol dm(- 3) KNO3 by potentiometric pH titration in pure water and water + metha nol, water + ethanol, water + N,N-dimethylformamide, water + dimethyl sulfoxide, and water + acetonitrile, pK(a) values increase with an inc rease in the concentration of the organic solvents. These results are discussed in terms of solvent characteristics. Solvent basicity and st abilization of the conjugate acid free base by hydrogen-bonding intera ctions in hydroorganic solvent media relative to pure aqueous media as well as proton-solvent interaction play an important role in the acid dissociation equilibrium.