Solvent and temperature effects on the solubility of syringic, vanillic or veratric acids: Experimental, modeling and solid phase studies

Abstract

The solubility of syringic acid, vanillic acid and veratric acid was measured in pure water and eleven organic solvents (methanol, ethanol, 1-propanol, 2-propanol, 2-butanone, ethyl acetate, acetonitrile, dimethylformamide, 1,2-propanediol, 1,3-propanediol and 1,3-butanediol), at 298.2 K and 313.2 K. Besides the solubility data, the melting temperatures and enthalpies of the solutes were determined by differential scanning calorimetry, while powder and single X-ray diffraction were used to resolve the solute solid structure, before and after the solubility studies. For modeling purposes, the NRTL-SAC model, also combined with the Reference Solvent Approach (RSA), and the Abraham solvation model were applied to describe the solid-liquid equilibria of the binary systems. A set of solvents was used to estimate the model parameters and afterwards, solubility predictions were carried out for binary systems not included in the correlation step. Better results were obtained using the Abraham solvation model with average relative deviations (ARD) of 15% for the correlation set and 26% for the predictions, which are more satisfactory than the results found with the NRTL-SAC model (33% for the correlation and 59% for the predictions) or the NRTL-SAC model combined with RSA (30% for the correlation and 59% for the predictions).

Solid-liquid phase equilibrium of trans-cinnamic acid, p-coumaric acid and ferulic acid in water and organic solvents: Experimental and modelling studies

“…In all cases, the solubility increases as the temperature increases, being larger in alcohols and 2-butanone and considerably smaller in water. This behavior was observed in previous works with benzoic acid derivatives [27,28]. Among the solutes studied, transcinnamic acid is the most soluble solute in all the organic solvents, whereas ferulic acid and p-coumaric acid have similar solubilities.…”

“…The results above show that both NRTL-SAC and NRTL-SAC þ RSA approaches adequately describe the solubilities of the studied compounds, presenting ARDs varying from 23% to 38%, which are satisfactory for this semi-predictive model and close to values obtained previously for similar binary systems [23,24,27,28]. Attempts to estimate the NRTL-SAC segment descriptors of transcinnamic and ferulic acids using the RSA were performed, but no significant improvements in the global ARDs were accomplished.…”

“…In previous works [27,28,41], the composition of the samples was quantified by gravimetry. However, tests showed that transcinnamic acid was thermally unstable, once it presented a weight loss of 6.3%, after remaining at 343.2 K for one week inside an oven, and a weight loss of 1.3% after one month at 303.2 K (along with significant color change in both cases).…”

“…( 5)). From our previous experience with benzoic acid derivatives [27,28], the robustness of the parameters relies in the number and diversity of systems included in the correlation. For instance, the inclusion of experimental solubility data in dimethylformamide (DMF) in the correlation set, considerably improved the overall predictions [28].…”

“…From our previous experience with benzoic acid derivatives [27,28], the robustness of the parameters relies in the number and diversity of systems included in the correlation. For instance, the inclusion of experimental solubility data in dimethylformamide (DMF) in the correlation set, considerably improved the overall predictions [28]. Therefore, data reported by Bradley et al [8] and Shakeel et al [14] for the solubility of trans-cinnamic acid and ferulic acid in another polar aprotic solvent, dimethyl sulfoxide (DMSO), were added to the same correlation set already used with the NRTL-SAC model.…”