Solubility Behavior, Hansen Solubility Parameters, and Thermodynamic Modeling of <sc>l</sc>-Leucine in 12 Monosolvents from 283.15 to 323.15 K

The solubility and solvent effects of l-leucine in monosolvent systems (water, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, acetonitrile, 1,4-dioxane, acetone, methyl acetate, and ethyl acetate) were investigated by the static gravimetric method in the temperature range from 283.15 to 323.15 K (with 5 K intervals). The solubility increased expectedly with the increase in temperature in all solvents. The solubility order of l-leucine in monosolvents was ranked as water > methanol > ethyl acetate > isopropanol > methyl acetate > isobutanol > ethanol > n-propanol > acetone >1,4-dioxane > acetonitrile > n-butanol. The polymorph of l-leucine was investigated by powder X-ray diffraction. Experiments confirmed that the crystal form did not change during the determination of solubility. The solubility of l-leucine in 12 monosolvents was analyzed by Dimroth and Reichardt's polarity parameters [E- T(30)], hydrogen bonds, cohesive energy density, molecular structures, viscosity, and Hansen solubility parameters. Solubility in these monosolvents was well correlated by the modified Apelblat model and the Yaws model. According to the Akaike information criterion and Akaike weight analysis, the modified Apelblat model achieves relatively better fitting results..