Thermochemistry of 2,5-Thiophenedicarboxylic Acid

Abstract

The enthalpies of combustion and sublimation of 2,5-thiophenedicarboxylic acid [CASRN 4282-31-9] were measured by rotary-bomb combustion calorimetry and the method of transference in a saturated stream of nitrogen, and the gas-phase enthalpy of formation was determined, Delta(f)H(o)(m)(g) = -(632.6 +/- 2.2) kJ x mol(-1). Standard ab initio molecular orbital calculations at the G2(MP2) and G3(MP2) levels were performed, and a theoretical study on the molecular and electronic structure of the compound has been carried out. The three most stable conformers have been explicitly taken into account. The calculated enthalpy of formation averaged using three different isodesmic reactions, -631.1 kJ x mol(-1), is in very good agreement with the experimental value. A comparison of the substituent effect of the carboxylic groups in benzene and thiophene ring has been made. The relative stability obtained for the substitution of two H atoms by COOH in position 2,5- for thiophene and 1,4- for benzene involve the same energetic effects, DeltaDelta(f)H(o)(m)= -747.6 +/- 2.4 and -748.2 +/- 2.7 kJ x mol(-1), respectively.

Assessment of Gaussian-4 theory for the computation of enthalpies of formation of large organic molecules

“…For three compounds with relatively large deviations (28,50,52), the D f H 298 values were also calculated from isodesmic reactions ( Table 5). The results for 28 support the G4 value calculated from atomization energy, thus questioning the experimental value.…”

Thermochemistry of substituted thiophenecarbonitrile derivatives

“…Despite the great research interest and the large number of applications of the thiophene derivatives, the thermochemical data available in the literature for these compounds is still very scarce and limited to the study of 2-and 3-thiophenecarboxylic acids [13], 2,5-thiophenedicarboxylic acid [14], 2-and 3-alkylsubstituted thiophenes [15], 2-and 3-thiopheneacetic acid, methyl esters [16], and 2-and 3-acetylthiophenes [17]. As a part of our broad interest on the thermochemistry of heterocycles and in order to enlarge the knowledge of the energetics of sulfur heterocycles and the understanding of the structural effects on thermodynamic stabilities of substituted thiophenes, through the enthalpies of formation of these compounds, in this paper we present the results of the determination of the standard molar enthalpies of formation and enthalpies of vaporization of five thiophenecarbonitrile derivatives.…”

The thermochemistry of alkanethiols and thioethers. Estimation of the enthalpies of formation of 1,3-dithiapropane and 1,3,5-trithiapentane

“…Experimental enthalpies of formation a of alkanes, alkanethiols and thioethers, used in this work, and calculated With the purpose of checking the accuracy of the estimated enthalpies of formation of the above mentioned two compounds, we have also carried out a theoretical study, calculating their enthalpies of formation at the G2(MP2), G2 and G3 levels. These methods have been previously used by us [21][22][23][24][25][26][27][28][29] for the calculation of the enthalpies of formation of different compounds containing S atoms: thiirane, 21 thiane, 21,22 1,3-and 1,4-dithiane, 21 1,3,5-trithiane, 22 2-and 3-thiophenecarboxylic acids, 23 thiane sulfoxide and thiane sulfone, 24 1,3-dithiane sulfone, 26 and 1,3-dithiane sulfoxide. 27 In all the cases, a good agreement between experimental and theoretical results was obtained.…”