Publications

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the crystalline state, of 1,5-diaminonaphthalene and 1,8-diaminonaphthalene were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static-bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the dependence of the vapour pressure of the solid isomers of diaminonaphthalene with the temperature, from which the standard molar enthalpies of sublimation were derived using the Clausius-Clapeyron equation. [GRAPHICS] Combining these two experimental values, the gas-phase standard molar enthalpies of formation, at T = 298.15 K, were derived and compared with those estimated using two different empirical methods of Delta fH degrees(m)(g) estimation: the Cox scheme and the Benson's Group Method. Moreover, the standard (p degrees = 0.1 MPa) molar entropies and Gibbs energies of sublimation, at T = 298.15 K, were derived for the two diaminonaphthalene isomers.

Abstract Despite the recent increase in the number of works addressing the effect of water on the thermophysical properties of ionic liquids (ILs), in particular densities and viscosities, the strong effect of the water content in the region of low water content on these properties requires further study for a deeper understanding of the phenomenon. Densities and viscosities of two imidazolium-based ionic liquids, 1-butyl-3-methylimidazolium dicyanamide [C(4)mim][N(CN)(2)] and 1-butyl-3-methylimidazolium tricyanomethane [C(4)mim][C(CN)(3)], and their binaries with water, for mole fractions up to 0.6, at atmospheric pressure and temperatures from (278.15 to 363.15) K were determined. The densities and viscosities of the pure ionic liquids and their binaries with water were described successfully by using several correlations. An extension to the Ye and Shreeve group contribution method shows a good agreement with the density data. An Orrick-Erbar-type approach and the Vogel-Tammann-Fulcher method were also applied to the experimental viscosity data, presenting a good agreement and allowing the estimation of new group contribution parameters, extending the applicability of these methods to new ILs. For mixtures, the one-constant Grunberg and Nissan equation was investigated for the correlation of the experimental viscosity binary mixture data of ILs + H(2)O, providing a good description of the experimental data using a single parameter for each ionic liquid studied.

Abstract The Knudsen mass-loss effusion technique was used for measuring the vapor pressures at different temperatures of the following 4-n-alkyloxybenzoic acids: 4-methoxybenzoic acid, between (340 and 362) K; 4-ethoxybenzoic acid, between (349 and 373) K; 4-propoxybenzoic acid, between (345 and 365) K; 4-butoxybenzoic acid, between (351 and 373) K; 4-pentyloxybenzoic acid, between (355 and 377) K; 4-hexyloxybenzoic acid, between (363 and 379) K; 4-heptyloxybenzoic acid, between (355 and 361) K; and 4-octyloxybenzoic acid, between (363 and 372) K. From the temperature dependence of the vapor pressure of each crystalline compound, the standard (p(0) = 10(5) Pa) molar enthalpies and Gibbs energies of sublimation, at T = 298.15 K, were derived. Differential scanning calorimetry was used in the study of phase transitions between condensed phases. The measured thermodynamic properties are compared with the results obtained on a previous similar study concerning the 4-n-alkylbenzoic acids series.

Abstract The gaseous phase heat capacity of benzoic acid (BA) was proven using the experimental technique called the "in vacuum sublimation/vaporization Calvet microcalorimetry drop method". To overcome known experimental shortfalls, the gaseous phase heat capacity of BA monomer was estimated by ab initio calculations and compared with experimental results. Gaseous phase heat capacities of BA were directly derived via calculated harmonic frequencies obtained by density functional theory (DFT) (B3LYP, BLYP, BP86, with 6-311++G(d,p), TZVP, cc-pVTZ basis sets) and the second-order Moller-Plesset theory, MP2/6-311++G(d,p). To increase the accuracy of estimation of the thermal properties, a procedure based on the calculation of the heat capacity from quantum chemical calculations in combination with a heat capacity balance of isodesmic reactions is described and applied to calculate the gaseous phase heat capacity, C(p,m), of the monomeric species over the temperature range of (298.15 to 600) K. The gaseous phase thermodynamic properties of the monomeric form of the BA were also derived from the assignment of the fundamental vibrational frequencies using experimental IR spectra. An excellent agreement among the experimental gaseous phase heat capacities, the results obtained using the proposed ab initio procedure, and the results derived from the assignment of fundamental vibrational frequencies was found. The results for the monomeric form of the BA, directly or indirectly obtained, and conclusions of this work strongly support the thesis that the gaseous phase heat capacity data as currently found in the literature are underestimated to the order of 20 To.

Abstract The synthetic power of the recently developed cascade annulations of beta-(hetero)aryl-alpha-nitro-alpha,beta-enals with the pyrrolidine-derived enamine of 2,2-dimethyl-1,3-dioxan-5-one is demonstrated by the first convergent route to (+/-)-tetrodotoxin.

Abstract Reported in the present work are the values of the gaseous standard (p degrees = 0.1 MPa) molar enthalpies of formation of 3-hydroxybenzaldehyde (3HBA), 4-hydroxybenzaldehyde (4HBA), and 3,5-di-tert-butyl-2-hydroxybenzaldehyde (3,5DTBHBA), at T = 298.15 K. For the three compounds, the values were derived from measurements of the standard molar energies of combustion of the crystalline compounds, using a static bomb calorimeter {Delta(c)H degrees m(3HBA) = -(3298.3 +/- 1.3) kJ . mol(-1) . Delta(c)H degrees(m)(4HBA) = -(3291.8 +/- 0.9) kJ . mol(-1) . Delta(c)H degrees(m)(3, 5DTBHBA) = -(8502.6 +/- 2.9) kJ . mol(-1)}, together with the standard molar enthalpies of sublimation, at T = 298.15 K, derived from the vapour pressures measured at different temperatures using the Knudsen effusion technique {Delta(g)(cr)H degrees m(3HBA) = (100.1 +/- 0.6) kJ . mol(-1) . Delta (g)(cr)H degrees(m)(4HBA) = (102.5 +/- 0.5) kJ . mol(-1), Delta(g)(cr)H degrees(m)(3, 5DTBHBA) = (96.0 +/- 0.5) kJ . mol(-1)}

Abstract Bread is consumed worldwide by man, thus contributing to the regular ingestion of certain inorganic species such as chloride. It controls the blood pressure if associated to a sodium intake and may increase the incidence of stomach ulcer. Its routine control should thus be established by means of quick and low cost procedures. This work reports a double-channel flow injection analysis (FIA) system with a new chloride sensor for the analysis of bread. All solutions are prepared in water and necessary ionic strength adjustments are made on-line. The body of the indicating electrode is made from a silver needle of 0.8 mm i.d. with an external layer of silver chloride. These devices were constructed with different lengths. Electrodes of 1.0 to 3.0 cm presented better analytical performance. The calibration curves under optimum conditions displayed Nernstian behaviour, with average slopes of 56 mV decade(-1), with sampling rates of 60 samples h(-1). The method was applied to analyze several kinds of bread, namely pao de trigo, pao integral, pao de centeio, pao de mistura, broa de milho, pao sem sal, pao meio sal, pao-de-leite, and pao de agua. The accuracy and precision of the potentiometric method were ascertained by comparison to a spectrophotometric method of continuous segmented flow. These methods were validated against ion-chromatography procedures.

Abstract The concentration of some anions (Cl, F, NO(3). and SO(4)). cations (Na, K, Ca, and Mg), pH and conductivity was determined in seven sampling points in the Serra da Estrela Mountains (Portugal) to verify if the application of road deicing with salt provokes impact in the water quality. Multivariate chemometric data analysis techniques of clustering and factor analysis were used. Preliminary analysis shows an overall conductivity increase in late spring and a decrease in late summer. A strong association between sodium chloride and the conductivity was observed by cluster analysis. Factor analysis supports the previous results and shows that the variation of the concentration of sodium chloride is the main source of the variance of the data along the year. In conclusion, the spreading of salt during the winter creates a local and seasonal impact on the water quality.

Abstract The mixed system between p-sulfonatocalix[4]arene and tetradecyltrimethylammonium bromide forms unilamellar vesicles after sonication of the aqueous dispersion. Furthermore these vesicles can be stored, without use of lyoprotectants, by lyophilization and then rehydration without change in size or shape.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation of 2-chloro-4,6-dinitroaniline and 4-chloro2,6-dinitroaniline, in the gaseous phase, at T = 298.15 K, were derived from the combination of the values of the standard molar enthalpies of formation, in the crystalline phase, and of the standard molar enthalpies of sublimation, at the same temperature. The standard molar enthalpies of formation, in the crystalline phase, were derived from the standard massic energies of combustion, in oxygen, measured by rotating-bomb combustion calorimetry. The standard molar enthalpies of sublimation were calculated, by the application of the Clausius-Clapeyron equation, to the vapour pressures at several temperatures, measured by Knudsen effusion technique. [GRAPHICS] The values of the standard molar enthalpies of formation of 2-chloro-4,6-dinitroaniline and 4-chloro2,6-dinitroaniline, in the gaseous phase, at T = 298.15 K, are discussed in terms of enthalpic increments, and the enthalpy of isomerization between the two compounds is compared with the same parameter for two isomers of chloronitroaniline, Studied in previous works.