Browsing by Author "Direito, Filipe"
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- Measurements and modeling of the solubility of naturally-occurring phenolicsPublication . Queimada, António; Mota, Fátima L.; Direito, Filipe; Pinho, Simão; Macedo, Eugénia A.Phenolic compounds are well known for their biological activity and, due to their reactivity, are important starting materials for the synthesis of complex molecules. These compounds can be obtained either by chemical synthesis or by extraction from different biological media. Thus, solubility in aqueous systems, organic and supercritical solvents are fundamental for a better design of reaction, separation and purification processes involving these molecules. For phenolics not many phase equilibria data are available. Usually, when data are reported, only a limited range of thermodynamic conditions is presented, and for many of the more complex phenolics data are extremely scarce or unavailable. In our laboratory we have been implementing a systematic study on the solubility of different hydroxybenzoic, phenylpropenoic and more complex phenolics in water and several organic solvents. Solubilities were determined using the analytical shake-flask method for generating the saturated solutions, followed by compositional analysis by Uv-vis spectrophotometry, HPLC and/or gravimetry [1,2]. A synthetic method based on the use of differential scanning calorimetry (DSC) for determining solubilities has also been investigated. For better understanding the solubilization process, melting properties (Tfus and DfusH) were determined by DSC and aqueous acid dissociation constants by potentiometric titration [1, 2]. Modeling was performed with the Cubic-plus-Association (CPA) equation of state, where a predictive methodology for obtaining the pure component parameters solely from the chemical structure is proposed. In this, the cubic parameters are obtained from correlations involving Tc, Pc and the van der Waals volume, while the association term parameters depend on the nature and position of each associating group [1,2]. Results showed that a good description of the solubility of phenolics using a single, small and temperature independent binary interaction parameter can be obtained in different solvents.
- Phase equilibria of phenolic compounds in aqueous, organic and supercritical solventsPublication . Queimada, António; Direito, Filipe; Mota, Fátima L.; Pinho, Simão; Macedo, Eugénia A.Phenolic compounds are relevant chemicals in industrial and biological processes. Their production, either by synthesis or extraction from biological media, requires the knowledge of phase equilibrium data that is lacking considerably in the open literature. For this reason, we have been performing at our laboratory a series of experimental measurements of solubility in water (1,2] and organic solvents, focused on two important families of phenolics: hydroxybenzoic and phenylpropenoic acids. The analytical shake flask method was employed for generating the saturated solutions, followed by quantitative analysis by Uv-vis spectrophotometry and/or gravimetry [1,2]. Alternatively, a synthetic method using DSC is being implemented, as this is faster and requires smaller amounts of solid. For a better understanding of the solubilization process, the corresponding melting properties were determined by DSC, with the exception of those phenolics that decompose upon melting, such as Do-coumaric, gallic and caffeic acids. For these, the Marrero and Gani group-contribution procedure [3] was used to generate estimates of the melting properties [1]. Since the studied molecules are organic acids, dissociation constants were also determined by potentiometric titratpon. As these compounds represent a class of associating molecules containing different associating groups such as hydroxyl and carboxyl (in many cases with, multiple substitutions), a new methodology for modeling these multifunctional compounds with the cubic-plus-association (CM) equation of state was developed. In this, the three cubic term parameters (a0, ci and b) are obtained from correlations involving the critical temperature and pressure, and van der Waals volumes, while the association term parameters depend on the nature and positron of each associating group (1,2]. Results showed that this methodology for the pure component parameters can lead to a good description of the aqueous solubility of phenolics using a single, small and temperature independent binary interaction parameter in the physical contribution of CPA. Further results for organic and supercritical solvents using the same methodology will be presented during the meeting.
- Solubility of phenolic compounds in water, organic and supercritical solventsPublication . Queimada, António; Mota, Fátima L.; Direito, Filipe; Pinho, Simão; Macedo, Eugénia A.Phenolic compounds represent a class of important chemicals with both biological and industrial importance. Their production, either by chemical synthesis or extraction from different biological media requires the adequate knowledge of phase equilibria. Particularly, the solubility in aqueous systems organic and supercritical solvents are fundamental for a better design of separation and purification processes.