THERMODYNAMIC MODELING OF SYSTEMS WITH BENZOIC ACID AS MODEL SYSTEMS FOR PHARMACEUTICALS

In this article, experimental investigation and thermodynamic modelling of benzoic acid (BA) solubility in organic solvents was made. Phase diagrams of binary systems of benzoic acid – benzophenone and benzoic acid – benzil were investigated by the thermal analysis methods. Phase diagrams are studied and eutectic coordinates in these systems were determinated. Eutectic point temperature (310.3 K) and composition of benzoic acid (18 mol. %) for benzoic acid – benzophenone system and eutectic point temperature (348.5 K) and mole fraction of benzoic acid (35 mol. %) for benzoic acid – benzil system were found. In the form of a linear relationship solubility curves of benzoic acid ln X = a – b/T, X – mole fraction BA, T – temperature in K in methyl acetate (a = 2.7748, b = 1389.7), ethyl acetate (a = 1.8099, b = 1102.6), n-propyl acetate (a = 0.9580, b = 854.2), n-butyl acetate (a = 1.2178, b = 902.0), n-pentyl acetate (a = 1.0719, b = 836.0), 1,4-dioxane (a = 0.0164, b = 406.0), chlorobenzene (a = 8.2765, b = 3268.4), n-decane (a = 12.332, b = 4916.9), n-dodecane (a = 14.623, b = 5808.1) were introduced. The solubility of benzoic acid in solvents at 298 K were calculated using the Hildebrand and Hansen solubility parameters. Comparison of the experimental and literature data was hold. Dependence of benzoic acid solubility on difference of the solubility parameters and the reduced radius was established. Models for the thermodynamic description of the solubility of substances in organic solvents are considered using benzoic acid as an example. Regular solution models with Hansen solubility parameters for express calculate solubility method of benzoic acid in organic solvents were recommended.