EFFECT OF ACIDIC, NEUTRAL AND BASIC pH ON SOLUBILITY AND PARTITION-COEFFICIENT OF BENZOIC ACID BETWEEN WATER-BENZENE SYSTEM

Solubilization is depends on solute-solvent interaction, dissociation of solute in solvent into ionic form, temperature, pressure, hydrogen bonding, dielectric constant, polarity and non-polarity of substance, pH, etc. Partition coefficient was determined in two immiscible solvents in aqueous and organic layer. Benzoic acid was selected for present study for its solubilization in different pH buffer solutions (acidic, neutral and basic) and for partition coefficient study at room temperature. Solubility of benzoic acid in different pH buffer solutions was analyzed by titration method. Most common two immiscible solvent such as water as hydrophilic solvent and benzene as hydrophobic solvent were selected for partition coefficient study. The drug benzoic acid was partitioned between these solvent by shake-flask method and analyzed the concentration of drug in both solvents by acid-base titration method. Solubility and distribution of benzoic acid between benzene-buffer solution of pH 4.0, 7.0, 9.0 and distilled water have been determined. It was observed that the benzoic acid remains un-dissociated monomer molecular form in aqueous layer and as dimer associated form in organic layer. Solubility of benzoic acid in distilled water was found to be 0.142 + 0.033 g/100 g of water and at different pH 4.0, pH 7.0 and pH 9.0 was found to be 0.153+0.01, 0.148+0.708 and 0.186 +0.145 respectively. Graphically it was observed that solubility in pH buffer solutions in acidic medium was slightly higher than basic pH. The partition coefficient of benzoic acid in benzene-water system was found to be 0.636 and in buffer solutions of pH 4.0, pH 7.0 and pH 9.0 were 0.841, 0.624 and 0.589 respectively. Graphically it was observed that partition coefficient of benzoic acid in acidic pH was higher than neutral and basic medium.