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

Abstract

A rotating-bomb combustion calorimeter was used to determine the standard ( p ∘ = 0.1 MPa) molar enthalpies of combustion, Δ c H m ∘ , of the liquids 2-acetyl-3-methylthiophene, 2-acetyl-4-methylthiophene, and 2-acetyl-5-methylthiophene, from which the standard molar enthalpies of formation, Δ f H m ∘ , in the liquid phase, at the temperature of 298.15 K, were derived. The standard molar enthalpies of vaporization, Δ l g H m ∘ , at T = 298.15 K, for those compounds, were obtained by high temperature Calvet microcalorimetry. Compounds - Δ c H m ∘ ( l ) /(kJ · mol −1) - Δ f H m ∘ ( l ) /(kJ · mol −1) Δ l g H m ∘ ( 298.15 K ) /(kJ · mol −1) 2-Acetyl-3-methylthiophene 4351.9 ± 1.8 148.0 ± 2.0 57.1 ± 2.4 2-Acetyl-4-methylthiophene 4344.5 ± 1.9 155.4 ± 2.1 63.0 ± 2.6 2-Acetyl-5-methylthiophene 4341.9 ± 1.8 158.0 ± 2.1 62.0 ± 2.6 From 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.