Browsing by Author "Alves, Rebeca S."
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- Contributions to the selection of solvents in the extraction of phenolic acidsPublication . Alves, Rebeca S.; Ferreira, Olga; Pinho, Simão; Campos, Leila Maria AguileraNaturally occurring phenolic acids are well-known and studied for their bioactive properties and wide distribution in plants, where they can be found in free form, or conjugated to other molecules. The study of the solubility of phenolic compounds in water and organic solvents is thus fundamental for the design of extraction, separation, crystallization and purification processes of great importance in the pharmaceutical, cosmetics and food industries. In this context, the main objective of this work is to measure the solubility of trans-cinnamic, p-coumaric and ferulic acids in water and in seven organic solvents (methanol, ethanol, 1-propanol, 2-propanol, 2-butanone, ethyl acetate and acetonitrile) at 298.2 K and 313.2 K and test the ability of the NRTL-SAC model, with or without the Reference Solvent Approach (RSA), and the Abraham solvation model to correlate, and preferably, predict the solubility data. To accomplish the objectives above the shake-flask method experimental method was combined with UV-Visible spectroscopy and gravimetric methods of analysis to perform the solubility measurements. In general, the results obtained were in close agreement with the very scarce information available in literature. After, the NRTL-SAC segment descriptors of each solute were fitted to solubility data in seven solvents, obtaining average relative errors (ARD) between 23% and 39%. The model was then applied to predict the solubility in other eight solvents, with ARD between 42% and 61%. The RSA was also applied, but no significant improvements were obtained relatively to the first approach. The optimization parameters of the Abraham solutes were also obtained by fitting the solubility data in six solvents for the trans-cinnamic and p-coumaric acids, and seven solvents for the ferulic acid, obtaining ARD between 7% and 24% for correlations and between 4% and 33% for the predictions in the remaining solvents. These values indicate Abraham's solvation model as the most suitable and very satisfactory model to predict the solubility of the selected solutes at 298.2 K.
- Solid-liquid phase equilibrium of trans-cinnamic acid, p-coumaric acid and ferulic acid in water and organic solvents: Experimental and modelling studiesPublication . Vilas-Boas, Sérgio M.; Alves, Rebeca S.; Brandão, Paula; Campos, Leila M.A.; Coutinho, João A.P.; Pinho, Simão; Ferreira, OlgaThe solubility of the trans isomers of cinnamic acid, p-coumaric acid and ferulic acid was measured in water and seven organic solvents (methanol, ethanol, 1-propanol, 2-propanol, 2-butanone, ethyl acetate and acetonitrile), at 298.2 K and 313.2 K, using the analytical shake-flask technique. The melting temperatures and enthalpies of the solutes were studied by differential scanning calorimetry, while solute solid structures were identified by powder and single X-ray diffraction. The NRTL-SAC model was applied to calculate the solubility of trans-cinnamic acid and trans-ferulic acid in pure solvents. For trans-p-coumaric acid, the NRTL-SAC was combined with the Reference Solvent Approach, as the solute melting properties could not be determined. The global average relative deviations (ARD) were 32% and 41%, in the correlation and prediction stages, respectively. The Abraham solvation model was also applied. The global ARD were 20% for correlation and 29% for predictions, which can be considered very satisfactory results for these semi-predictive models.
- Solvent and temperature effects on the solubility of syringic, vanillic or veratric acids: Experimental, modeling and solid phase studiesPublication . Vilas-Boas, Sérgio M.; Vieira, Vanessa; Brandão, Paula; Alves, Rebeca S.; Coutinho, João A.P.; Pinho, Simão; Ferreira, OlgaThe 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 diffractionwere used to resolve the solute solid structure, before and after the solubility studies. Formodeling purposes, theNRTL-SACmodel, also combinedwith 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).