Determination of l-Valine Solubility in 12 Monosolvent Systems at Multiple Temperatures from 283.15 to 323.15 K

The solubility data of l-valine were measured by the static gravimetric method in 12 pure solvents (water, methanol, acetonitrile, 1,4-dioxane, n-propanol, isopropanol, ethanol, acetone, methyl acetate, ethyl acetate, n-butanol, and isobutanol) at 283.15–323.15 K (except for 1,4-dioxane at 288.15–328.15 K) and 101.2 kPa. The increasing temperature shows a positive effect on l-valine solubility in all the solvents. In addition, the solubility sequence of l-valine at 298.15 K is water > methanol > ethanol >1,4-dioxane > isobutanol > acetone > n-butanol > ethyl acetate > acetonitrile > methyl acetate > isopropanol > n-propanol. The polymorphism of l-valine was investigated by the powder X-ray diffraction test, and the patterns show that there is no crystal transformation in the process of solubility measurement. The main factors influencing the solubility behavior include solvent polarity (ET(30)), hydrogen bond, cohesive energy density, and Hansen solubility parameters (HSPs). Two mathematical models, i.e., the modified Apelblat model and the Yaws model, were applied to correlate the measured solubility data. The ARDs, RMSDs, AIC, and Akaike weights were calculated to evaluate the fitting results.