Solubility determination and thermodynamics modeling of n-alkyl-parabens in short-chain alcohols from (288.15 to 318.15) K

The well-established preservative and antimicrobial effect of alkyl parabens result in its wide application in the food, cosmetics, and pharmaceutical industries and motivates the solubility data obtaining. In this work, the solubility of parabens (methyl-, ethyl-, propyl-, and butyl-) in short-chain alcohols (ethanol, n-propanol, and 2propanol) was experimentally determined by the gravimetric method from 288.15 to 318.15 K. Different thermodynamic models (Wilson, NRTL, UNIFAC; and COSMO-SAC models) were applied to correlate the experimental data. In general, the mole fraction of parabens increased with increasing temperature, following the order butyl > propyl > ethyl > methyl parabens in the three investigated solvents. Wilson and NRTL models presented a good correlation, according to the calculated values of mean squared deviation (RMSD) and absolute deviation (AD), while the UNIFAC showed high deviations, which was expected because it is not an adjustable model. The COSMO-SAC model has been compared to experimental data and helped understand the solute-solvent interactions. The sigma profile (a-profile) of the molecules obtained by COSMO-SAC showed that alkyl parabens have similarities to ethanol, n-propanol, and 2-propanol. Additionally, the solubility of the parabens increased with the chain size due to the increase in their lipophilicity. This fact corroborated with the experimental data obtained. The solubility was also favored with the temperature increasing. Thus, a determination of the solubility of parabens in different solvents was collected to obtain complete physicochemical data, contributing to the projection and expansion of industrial applications of these compounds as excipients in liquid formulations.