Publications

Abstract The standard molar enthalpy of formation at T = 298.15 K of 6-chloro-2,3-dimethylquinoxaline 1,4-dioxide in the gas-phase was derived using the values of the enthalpies of combustion for the crystalline solid, measured by using totating-bomb combustion calorimetry, and of the enthalpies of sublimation, measured by using Calvet microcalorimetry. This value was used for calibrating the computational procedure employed to estimate the gas-phase enthalpies of formation for the deoxygenated quinoxaline derivatives and also to compute the first, second, and mean (N-O) bond dissociation enthalpies in the gas-phase. The B3LYP/6-311+G(2d,2p) calculations were also extended to the fluorine, bromine, and iodine derivatives and to the isomers with a halogen substituted at position 5. When the halogen atom enters the same position in the quinoxaline ring, it was found that the substituent had almost no influence on the computed (N-O) bond dissociation enthalpies, except for 5-fluoro-2,3-dimethylquinoxaline 1,4-dioxide.

Abstract The huge number of possible combinations of binary mixtures of alcohols and ionic liquids (ILs) make the exhaustive measurement of all these systems impracticable requiring the use of a predictive model for their study. In this work, the predictive capability of COSMO-RS, a model based on unimolecular quantum chemistry calculations, was evaluated for the description of the liquid-liquid equilibria and the vapour-liquid equilibria of binary mixtures of alcohols and several imidazolium and pyridinium-based ILs. The effect of the ions and alcohols conformers on the quality of the predictions was assessed and the quantum chemical COSMO calculation at the BP/TZVP level derived from the lower energy conformations was adopted. Although a degradation in the liquid-liquid equilibria predictions with increasing size length of the alkyl chain of the alcohol or of the ionic liquid and with the short chain alcohol methanol in the vapour-liquid equilibria predictions were observed, in general a reasonable qualitative agreement between the model predictions and experimental data for a large combination of structural variations of both alcohols and ILs was obtained. COSMO-RS can thus be very useful in the scanning of the growing number of known ILs to find suitable candidates, or help designing new ILs, for specific applications before extensive experimental measurements.

Abstract Ionic liquids (ILs) are a novel class of chemical compounds with interesting properties that are driving a lot of research in several fields. For ionic liquids to be effectively used as solvents in liquid-liquid extractions, the knowledge of the mutual solubilities between ILs and the second liquid phase is fundamental. Furthermore, while ILs cannot volatilise and lead to air pollution, even the most hydrophobic ones present some miscibility with water posturing secondary aquatic environmental risks. Despite the importance of the ILs and water systems, there are few extensive reports on their phase equilibria. The aim of this work is to discuss and understand the mutual solubilities of water and imidazolium-based ILs. The results indicate that these mutual solubilities are primarily defined by the anion followed by the cation alkyl side chain length. It was also found that the solubility of the studied ILs in water is more dependent on the ILs structural modifications than the solubility of water in those ILs. The substitution of the most acidic hydrogen in the imidazolium cation by a methyl group leads to different behaviours in both rich-phases, where the solubility of water in ILs showed to be more hydrogen bonding dependent. From the solubility results it can be concluded that the hydrophobicity of the anions increases in the order [BF4](-) < [CH3(C2H4O)(2)SO4](-) < [C(CN)(3)](-) < [PF6](-) < [N(SO2CF3)(2)](-) while the hydrophobicity of the cations increases, as expected, with the alkyl chain length increase.

Abstract This letter reports the importance and advantages of the constraints in the Redlich-Peterson isotherm exponent. (C) 2007 Published by Elsevier B.V..

Abstract The standard (p degrees = 0.1 MPa) molar energies of combustion in oxygen, at T= 298.15 K, of two crystalline bis(N,N-diethylthioureas) R(CONHCSNEt2)(2): pyridine-2,6-dicarbonyl-bis(N,N-diethylthiourea), R = pyridyl. abbreviated as (bis-py-DETU). and adipoyl-dicarbonyl-bis(N,N-diethylthiourea), R = (CH2)(4), abbreviated as (bis-ad-DETU). were measured by rotating bomb calorimetry so, the standard molar enthalpies of formation of both compounds, in their crystalline phase, were derived. [GRAPHICS] Furthermore, the energetics of the title compounds were studied by means of density functional theory Calculations at the B3LYP/6-311G(dp) level of theory.

Abstract The standard (p = 0.1 MPa) molar enthalpies of combustion in oxygen of five N-thenoylthiocarbamic-O-n-alkylesters, C4H3SCO-NHCSOR, R = Et (Httee), n-Pr (Httpe), n-Bu (Httbe), n-Pen (Httpene), and n-Hex (Htthe), were measured, at T = 298.15 K, by rotating-bomb calorimetry. The standard molar enthalpies of sublimation of these compounds were determined using Calvet microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the title compounds, in their crystalline and gaseous phases, respectively. Furthermore, differential scanning calorimetry was applied in order to measure the temperatures and enthalpies of fusion for all compounds. Entropies of fusion were derived from the experimental results and the odd and even effect was found. [GRAPHICS]

Abstract Batch processes were carried out for the photocatalytic degradation of Acid Red 151 from its aqueous solution using ZnO catalyst at different initial dye concentrations. The process was found to be diffusion controlled for the first 15-20 minutes (before irradiation) with an average diffusion coefficient of 6.759 × 10 -6 cm 2/s. The photocatalytic degradation kinetics was analyzed using the first order, second order and Langmuir-Hinshelwood expressions by linear and non-linear method. The four types of second order kinetic and Langmuir-Hinshelwood kinetic models were also discussed. Non-linear method is a better way to obtain the kinetic parameters. The photocatalytic degradation process was found to follow first order kinetics at lower substrate concentrations and second order kinetics at higher substrate concentrations. © 2007 Science &amp; Technology Network, Inc.