Measurement and Correlation of Solubilities of 4-Methylbenzoic Acid and Terephthalic Acid in Eight Organic Solvents

In this study, the solubility of 4-methylbenzoic acid and terephthalic acid in N-methylformamide, 1,3-dimethyl-2-imidazolidinone, N-methylformanilide, 2-ethyl-1-hexanol, tetrahydrofuran, cyclohexanone, acetophenone, and ethylene glycol diethyl ether was measured using the laser dynamic method under 101.3 kPa at the temperature ranging from 293.65 to 344.35 K. The measured results showed that the solubility of 4-methylbenzoic acid and terephthalic acid increased with the increasing temperature. The solubility of 4-methylbenzoic acid is greater than that of terephthalic acid in the same solvents. The modified Apelblat model and the modified nonrandom two-liquid (NRTL) activity coefficient model were utilized to correlate the solubility of 4-methylbenzoic acid and terephthalic acid in each solvent. The calculated solubility agreed satisfactorily with the measured results with 1.67/1.91% averaged relative deviation (ARD) for terephthalic acid and 0.62/0.69% for 4-methylbenzoic acid in the modified NRTL/Apelblat model, respectively. The result of the Akaike Information Criterion (AIC) analysis showed that the modified Apelblat model was better at correlating the solubility of 4-methylbenzoic acid in 1,3-dimethyl-2-imidazolidinone, ethylene glycol diethyl ether, tetrahydrofuran, acetophenone, N-methylformamide, acetophenone, and terephthalic acid in 1,3-dimethyl-2-imidazolidinone; the modified NRTL model performs better in correlating the solubility of 4-methylbenzoic acid in N-methylformanilide, N-methylformamide, 2-ethyl-1-hexanol, and terephthalic acid in 2-ethyl-1-hexanol, 2-ethyl-1-hexanol, and cyclohexanone N-methylformanilide.