Calorimetric study of methyl and ethyl 2-thiophenecarboxylates and ethyl 2- and 3-thiopheneacetates

The standard (p∘=0.1MPa) molar enthalpies of formation, in the condensed phase, of the liquids methyl 2-thiophenecarboxylate, ethyl 2-thiophenecarboxylate, ethyl 2-thiopheneacetate, and ethyl 3-thiopheneacetate, at T = 298.15 K, were derived from the standard massic energies of combustion, in oxygen, to yield CO2 (g) and H2SO4 · 115H2O (aq), measured by rotating bomb combustion calorimetry. For these four compounds, the standard molar enthalpies of vaporization, ΔlgHm∘, at T = 298.15 K, were obtained by high temperature Calvet microcalorimetry. The values obtained were:Compound-ΔfHm∘(l)/(kJ·mol-1)ΔlgHm∘(298.15K)/(kJ·mol-1)Methyl 2-thiophenecarboxylate (l)301.2 ± 1.757.6 ± 1.2Ethyl 2-thiophenecarboxylate (l)327.2 ± 2.056.6 ± 1.3Ethyl 2-thiopheneacetate (l)361.8 ± 2.361.8 ± 1.3Ethyl 3-thiopheneacetate (l)358.9 ± 2.263.2 ± 1.3Full-size tableTable optionsView in workspaceDownload as CSVThe standard (p∘=0.1MPa) molar enthalpies of formation, in the gaseous phase, were derived from the experimental results and they are interpreted in terms of enthalpic increments of the introduction of a methylene group to the substituent chain. Moreover, the results are compared with the analogue benzene derivative.