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Abstract  

The standard (pº = 0.1 MPa) molar enthalpies of formation in the condensed state of chromone-3-carboxylic acid and coumarin-3-carboxylic acid were derived from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by combustion calorimetry. The standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry. From these values the standard molar enthalpies in the gaseous phase, at T = 298.15 K, were derived. Additionally estimates of the enthalpies of formation, of all the studied compounds in gas-phase, were performed using DFT and other more accurate correlated calculations (MCCM and G3MP2), together with appropriate isodesmic, homodesmic or atomization reactions. There is a reasonable agreement between computational and experimental results.

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Abstract  

This paper demonstrates the application of thermal analysis in compatibility and stability studies between an ACE inhibitor (enalapril maleate) and excipients. The results have helped to elucidate the reason of a stability problem observed during the storage of enalapril maleate tablets. Incompatibility between enalapril maleate and colloidal silicon dioxide was detected. Besides, it was confirmed that the reaction between enalapril maleate and NaHCO3 increases the thermal stability of the drug. This study supports the importance of using thermoanalytical methods in the development of pharmaceuticals.

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Abstract  

The synthesis and characterization of lanthanide(III) citrates with stoichiometries 1:1 and 2:3; [LnL·xH2O] and [Ln2(LH)3·2H2O], Ln=La, Ce, Pr, Nd, Sm and Eu are reported. L stands for (C6O7H5)3− and LH for (C6O7H6)2−. Infrared absorption spectra of both series evidence coordination of carboxylate groups through symmetric bridges or chelation. X-ray powder patterns show the amorphous character of [LnL·xH2O]. The compounds [Ln2LH3·2H2O] are crystalline and isomorphous. Emission spectra of Eu compounds suggest C 2v symmetry for the coordination polyhedron of [LnL·xH2O] and C 4v for [Ln2(LH)3·2H2O]. Thermal analyses (TG-DTG-DTA) were carried out for both series. The thermal analysis patterns of the two series are quite different and both fit in a 4-step model of thermal decomposition, with lanthanide oxides as final products.

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Abstract  

Excess molar enthalpies of the ternary mixture {x 1 tert-butyl methyl ether (MTBE)+x 2 ethanol+(1–x 1x 2) hexane} and, the involved binary mixtures {x tert-butyl methyl ether (MTBE)+(1–x) ethanol}, {x tert-butyl methyl ether (MTBE)+(1–x) hexane} and {x ethanol+( 1–x) hexane} have been measured at 298.15 K and atmospheric pressure, over the whole composition range, using a Calvet microcalorimeter. The results were fitted by means of different variable degree polynomials.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Mato, S. Cebreiro, J. Legido, and M. Paz Andrade

Abstract  

Experimental excess molar volumes for the ternary system {x 1MTBE+x 21-propanol+(1–x 1x 2)nonane} and the three involved binary mixtures have been determined at 298.15 K and atmospheric pressure. Excess molar volumes were determined from the densities of the pure liquids and mixtures, using a DMA 4500 Anton Paar densimeter. The ternary mixture shows maximum values around the binary mixture MTBE+nonane and minimum values for the mixture MTBE+propanol. The ternary contribution to the excess molar volume is negative, with the exception of a range located around the rich compositions of 1-propanol. Several empirical equations predicting ternary mixture properties from experimental binary mixtures have been applied.

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Ternary mixture MTBE+1-pentanol+nonane at 298.15 K and atmospheric pressure

Measurements and analysis of densities and excess molar volumes

Journal of Thermal Analysis and Calorimetry
Authors: P. Verdes, M. Mato, J. Legido, and M. Paz Andrade

Abstract  

Densities at 298.15 K and atmospheric pressure have been measured, using a DMA 4500 Anton Paar densimeter, for the ternary mixture methyl tert-butyl ether (MTBE)+1-pentanol+nonane and for the involved binary mixture 1-pentanol+nonane. In addition, excess molar volumes were determined from the densities of the pure liquids and mixtures. Suitable fitting equations have been used in order to correlate adequately the excess molar volumes. Experimental data were also used to test several empirical expressions for estimating ternary properties from experimental binary results.

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Excess molar enthalpies of dichloropropane + n-alkane mixtures

Study on the effect of increasing the chain length of the n-alkane and the influence of the chlorine position

Journal of Thermal Analysis and Calorimetry
Authors: M. Mato, J. Fernández, J. Legido, and M. Paz Andrade

Abstract  

We have determined the excess molar enthalpies
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at 298.15 K and normal atmospheric pressure for the binary mixtures containing dichloropropane and n-alkane [{xCH2ClCHClCH3 + (1−x) CnH2n+2 (n = 6, 8, 10, 12)} and {xCH2ClCH2CH2Cl + (1−x) CnH2n+2 (n = 8, 10)}] using a Calvet microcalorimeter. The
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values for all the mixtures show endothermic behaviour for the whole composition range. The Redlich–Kister equation was used to correlated the experimental values. The experimental excess molar enthalpies were examined on basis of the DISQUAC group-contribution model and the UNIFAC group-contribution method using the version considered by Larsen et al. The experimental and calculated results are discussed in terms of molecular interactions and the proximity effect.
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Abstract  

The thermal decomposition of asphaltenes is mainly responsible for the formation of coke in petroleum processing. Phenomena involved are not clearly understood, because of the difficulties to characterize such heavy components. This paper reports the application of thermal analysis techniques to study the thermal behavior of asphaltenes from Brazilian oil. The approach involves kinetic studies of the thermal decomposition of asphaltenes under controlled conditions by thermogravimetry (TG), characterization of volatile fractions by thermogravimetry and differential thermal analysis coupled with gas chromatography/mass spectrometry (TG-DTA/GC/MS) and by gas chromatography/mass spectrometry (GC/MS) in the volatile recovered. The coke formed was also studied after being decomposed into smaller molecules using selective oxidation.

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Abstract  

A simplified RC model which simulates the operation mode of an isothermal titration calorimeter (ITC), when it is used in a continuous mode to determine heat of mixing, is proposed. The model takes into account several thermal effects that are evident in the mixing process and it must be identified and quantified to determine reliable values of heat of mixing. The main effects considered in the development of the model were those caused by: (i) the difference between the temperatures of the injected liquid and the mixture, (ii) the increase in heat capacity of the mixture and the thermal conductance of the couplings between the mixture and its surroundings and (iii) the changes in the power dissipated by stirring after injection. A good agreement between model and experimental results is observed.

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