Solubility Behavior and Polymorphism of N-Acetyl-l-proline in 16 Individual Solvents from 283.15 to 323.15 K

The mole fraction solubility data of N-acetyl-l-proline in 16 neat solvents (water, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, n-pentanol, acetone, 2-butanone, acetonitrile, dichloromethane, methyl acetate, ethyl acetate, and 1,4-dioxane) covering a temperature range of 283.15–323.15 K were measured by the static gravimetric method. The polymorphism of N-acetyl-l-proline was investigated by the powder X-ray diffraction test and the patterns show that there are two polymorphs within the studied solid–liquid equilibrium systems. The increasing temperature shows a positive effect on N-acetyl-l-proline solubility in all of the solvents and the largest increasing rate is observed in acetonitrile with an increase of 16-fold. The solubility behavior was found to be influenced by five factors including polarity, hydrogen bonding, solvent–solvent interactions, molecular construction, and viscosity. Two thermodynamic models, i.e., the modified Apelblat model and the Yaws model, were used for the correlation of solubility data. To evaluate the fitting results, the average relative deviation (ARD) and root-mean-square deviation (RMSD), as well as the Akaike information criterion (AIC) and Akaike weights, were computed for each model.