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Abstract  

The present work is part of a broader research program on the energetics of formation of heterocycles, aiming the study of the enthalpic effects of the introduction of different substituents into heterocycles. In this work we present the results of the thermochemical research on sulphur heterocycles of the type substituted thiophenes with different kind of substituents, mainly alkyl, ester, acetyl, carboxamide, acetamide, carbonitrile and carboxaldehyde. The standard (p o=0.1 MPa) molar enthalpies of formation, in the condensed phase, at T=298.15 K, of a large number of substituted thiophenes, were derived from their standard massic energies of combustion, measured by rotating-bomb combustion calorimetry, while the standard molar enthalpies of vaporization or sublimation of those compounds were obtained either by high temperature Calvet Microcalorimetry, or by the temperature dependence of their vapour pressures determined by the Knudsen effusion technique. The standard molar enthalpies of formation, of the studied sulphur heterocycles in the gaseous phase, were then derived. The results are interpreted in terms of structural contributions to the energetics of the substituted thiophenes, the internal consistency of the results is discussed and, whenever appropriate and possible, empirical correlations are suggested for the estimation of standard molar enthalpies of formation, at T=298.15 K, of substituted thiophenes. A Table of enthalpic increments for different group substituents in positions 2 or 3 of the thiophene ring has been established.

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Thermochemical properties of two nitrothiophene derivatives

2-acetyl-5-nitrothiophene and 5-nitro-2-thiophenecarboxaldehyde

Journal of Thermal Analysis and Calorimetry
Authors: Manuel Ribeiro da Silva and Ana Santos

Abstract  

This article reports the values of the standard (p o = 0.1 MPa) molar enthalpies of formation, in the gaseous phase,
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $${{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{g}} \right),$$ \end{document}
at T = 298.15 K, of 2-acetyl-5-nitrothiophene and 5-nitro-2-thiophenecarboxaldehyde as −(48.8 ± 1.6) and (4.4 ± 1.3) kJ mol−1, respectively. These values were derived from experimental thermodynamic parameters, namely, the standard (p o = 0.1 MPa) molar enthalpies of formation, in the crystalline phase,
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $${{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{cr}} \right) ,$$ \end{document}
at T = 298.15 K, obtained from the standard molar enthalpies of combustion,
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $${{\Updelta}}_{\text{c}} H_{\text{m}}^{\text{o}} ,$$ \end{document}
measured by rotating bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from the temperature–vapour pressure dependence, obtained by the Knudsen mass loss effusion method. The results are interpreted in terms of enthalpic increments and the enthalpic contribution of the nitro group in the substituted thiophene ring is compared with the same contribution in other structurally similar compounds.
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bases (TCA, DAT and DCA) ( Fig. 1 ) have been synthesized by the condensation of equimolar ratio of 2-thiophenecarboxaldehyde with 4-anisidine (TCA) and 3,4-dihydroxy-5-nitrobenzaldehyde with 2-amino-5-methylthiazole (DAT) and 4-chloroaniline (DCA

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