Experimental thermochemical study of the three methyl substituted 2-acetylthiophene isomers

A rotating-bomb combustion calorimeter was used to determine the standard (p∘ = 0.1 MPa) molar enthalpies of combustion, ΔcHm∘, of the liquids 2-acetyl-3-methylthiophene, 2-acetyl-4-methylthiophene, and 2-acetyl-5-methylthiophene, from which the standard molar enthalpies of formation, ΔfHm∘, in the liquid phase, at the temperature of 298.15 K, were derived.The standard molar enthalpies of vaporization, ΔlgHm∘, at T = 298.15 K, for those compounds, were obtained by high temperature Calvet microcalorimetry. Compounds-ΔcHm∘(l)/(kJ · mol−1)-ΔfHm∘(l)/(kJ · mol−1)ΔlgHm∘(298.15K)/(kJ · mol−1)2-Acetyl-3-methylthiophene4351.9 ± 1.8148.0 ± 2.057.1 ± 2.42-Acetyl-4-methylthiophene4344.5 ± 1.9155.4 ± 2.163.0 ± 2.62-Acetyl-5-methylthiophene4341.9 ± 1.8158.0 ± 2.162.0 ± 2.6Full-size tableTable optionsView in workspaceDownload as CSVFrom the experimental results, the standard molar enthalpies of formation of the three methyl substituted 2-acetylthiophene isomers, in the gaseous phase, were calculated and a comparison between the relative stability and the energetic of the three isomers was carried out.