In this study, the solubility of phthalic acid and o-toluic acid in propionic acid, N-methylformamide, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), and acetonitrile are measured under atmospheric pressure (101.3 kPa) by the method of laser dynamics. The experimental temperature range is 286.35 to 338.75 K. The measured data shows that the solubility of phthalic acid and o-toluic acid increases with increasing temperature in the temperature range studied. The experimental data are correlated by the Apelblat model, the λh model, and the modified nonrandom two liquid activity coefficient model, and the calculated solubility is in agreement satisfactorily with the measured results. Akaike information criterion analysis results show that the Apelblat model was the most suitable model to correlate the solubility of phthalic acid in propionic acid, N-methylformamide, and DMSO and the solubility of o-toluic acid in propionic acid, DMSO, and NMP; the λh model was the most suitable model to correlate the solubility of phthalic acid in DMF and DMAC and the solubility of o-toluic acid in N-methylformamide and DMF; and the modified NRTL model was the most suitable model to correlate the solubility of phthalic acid in NMP and acetonitrile and the solubility of o-toluic acid in DMAC and acetonitrile.

In this work, with the available solid–liquid equilibrium (SLE) data of six aromatic carboxylic acids, aromatic dicarboxylic acid isomers (terephthalic acid (TPA), isophthalic acid (IPA), and phthalic acid (PA)), and methyl benzoic acid isomers (m-toluic acid (m-TA), o-toluic acid (o-TA), and p-toluic acid (p-TA)) in acetic acid (HOAc) + water (H2O) solvent mixtures, the relationship between the molecular structure of the above aromatic carboxylic acids and the solubility of them in HOAc + H2O solvent mixtures is discussed. It could be found that among the aromatic dicarboxylic acid isomers and methyl benzoic acid isomers, TPA and p-TA have the lowest solubility in the same solvent and temperature, respectively. Meanwhile, three new groups, p-ArCOOH, m-ArCOOH, and o-ArCOOH, in the UNIFAC (Dortmund) model were first defined to distinguish the influence of the positions of ArCOOH on the thermodynamic properties of aromatic carboxylic acid isomers, which indicates that ArCOOH is located in the para, meta, and ortho positions of the ArCOOH or ArCH3 groups, respectively. Then, the interaction parameters of ArCOOH, p-ArCOOH, m-ArCOOH, and o-ArCOOH with other involved groups in the solvent systems are first obtained by regressing these available SLE data. By using the new defined group, the UNIFAC (Dortmund) model was used to correlate SLE data for the above ternary systems, and trimesic acid + HOAc + H2O systems agree with the experimentally measured results satisfactorily.