Solid–Liquid Phase Equilibrium Characteristics and Thermodynamic Analysis of Asymmetric Schiff Base Ligands and Their Organic Phenol-Aluminum Compounds

In this work, a static analysis method was used to measure the solubility of nine compounds: C1 and C2 in three solvents, C3 in four solvents, and C4–C7 in four pure solvents, with temperatures ranging from 268.15 to 328.15 K (measurements in p-xylene were performed over the temperature interval of 288.15 to 328.15 K, whereas for other systems, the experimental temperature range was maintained between 268.15 and 308.15 K). Experimental results demonstrate enhanced solubility for all compounds at selected temperatures. Solubility data were correlated using seven thermodynamic models: Yaws, polynomial, van’t Hoff, λh, Wilson, NRTL, and UNIQUAC, yielding superior fits characterized by an average absolute relative deviation (ARD) below 5% and root-mean-square deviation (RMSD) under 0.2%. Among these, the polynomial model exhibited optimal performance for empirical correlations, whereas the NRTL model provided the best fit among activity coefficient models. Solvent-dependent solubility variations were further elucidated through Hansen solubility parameters. Thermodynamic calculations confirmed dissolution to be endothermic and entropy-driven in most systems. The measured solubility and fusion enthalpy data establish fundamental references for optimizing homogeneous catalysis and crystallization processes of organic aluminum compounds.