Solubility Measurements and Thermodynamic Modeling of Salen Ligand and Organoaluminum-Salen Complex in Selected Solvents

Solvent selection plays a significant role in the purification process and homogeneous reaction. Solubility data is the most intuitive data to reflect the dissolution effect. The solubility of N, N′ - bis - (salicylaldehyde) ethylenediamine (1) (SalenH2) and N, N′ - ethylenebis (salicylideneiminato) methylaluminum (2) (SalenAlMe) in selected solvents was measured from 268.15 K to 318.15 K under an inert atmosphere. All the operations were carried out using standard Schlenk line techniques or in a glove box. The difference in solubility can be attributed to cohesive energy density, polarity, steric hindrance, as well as intermolecular interactions. Van't Hoff equation, Apelblat model, Polynomial equation, NRTL model, Wilson model, and UNIQUAC model were applied for correlating the experimental solubility data. These thermodynamic models were evaluated by the average relative deviation (ARD). Among those, the Apelblat model had wide applicability with an average ARD < 2%. The NRTL model showed the best correlation results for compound 1 in aprotic solvents with an average ARD of 0.74%, and the correlation of the Polynomial equation was significantly greater for compound 2 with an average ARD of 0.71%. The results of model correlation can be used to predict the solubility of compounds 1 and 2. Furthermore, apparent thermodynamic functions were calculated. It was proved that the dissolution process was entropy-increasing endothermic under the experimental conditions. The experiment data would be essential for optimizing purification and recrystallization processes, as well as the design of homogeneous catalysis for compounds 1 and 2 in industry.