Experimental Measurement and Correlation of Solubility Data and Thermodynamic Properties of Protocatechuic Acid in Four Organic Solvents

Using a thermostated reactor and UV/vis spectrophotometer analysis, the solubility of protocatechuic acid (PA) in ethanol, methanol, methyl acetate, and ethyl acetate was measured from (293.15 to 318.15) K at atmospheric pressure. The effect of solvent type and temperature on the solubility are discussed. The relative solubility of protocatechuic acid in different solvents was determined in descending order to be x methanol > x ethanol > x methyl > x ethyl . The experimental solubility data of the solutes (PA) in four pure solvents was correlated with the modified Apelblat equation and semiempirical Buchowski–Ksiazczak λh equation. Dissolution standard molar enthalpy Δ sol H ° (kJ·mol –1 ), Gibbs energy Δ sol G ° (kJ·mol –1 ), and entropy Δ sol S ° (J·mol –1 ·K –1 ) of protocatechuic acid were estimated using the solubility data: