Dissolution Behavior of 1H-Indole-3-carbaldehyde in 15 Monosolvents: Solubility, Hansen Solubility Parameters, and Mixing Thermodynamic Properties

The molar fraction solubility of 1H-indole-3-carbaldehyde (IAld) was obtained by static gravimetric method in acetone, acetonitrile, methyl acetate, ethyl acetate, n -propyl acetate, isopropyl acetate, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, isobutanol, 2-butanol, 1-pentanol, and 2-methyl-2-butanol from 283.15 to 323.15 K. Of the selected solvents, at 298.15 K, acetone has the largest molar fraction solubility (2.0119 × 10 –2 ), while isopropyl acetate has the least (0.5228 × 10 –2 ). Two empirical equations (λh and modified Apelblat equation) and two activity coefficient models (Wilson model and NRTL model) were used to correlate with the experimental data, with the modified Apelblat equation showing the optimal fitness (average relative deviation ARD: 1.492%, root-mean-square deviation RMSD: 0.018%). The Spearman rank correlation coefficient of the solvent shows that the hydrogen bond (0.62) is more significant than polarity (−0.14) and cohesive energy density (0.26). The Hansen Solubility Parameters analysis, jointly with the intermolecular interaction energy calculated by COSMO-RS and the molecular electrostatic potential (MEP), indicates that the molecular structure of the solvents could also affect the dissolution process. Moreover, the mixing thermodynamic properties reveal that the mixing process is driven by entropy and is spontaneous.