Energetics of thiophenecarboxaldehydes and some of its alkyl derivatives

Abstract

The standard ( p ∘ = 0.1 MPa) molar enthalpies of combustion, Δ c H m ∘ , for the liquids 2-thiophenecarboxaldehyde, 3-thiophenecarboxaldehyde, 3-methyl-2-thiophenecarboxaldehyde, 5-methyl-2-thiophenecarboxaldehyde, and 5-ethyl-2-thiophenecarboxaldehyde were determined, at the temperature of 298.15 K, using a rotating-bomb combustion calorimeter. For these five compounds, the standard molar enthalpies of vaporization, Δ l g H m ∘ , at T = 298.15 K 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-Thiophenecarboxaldehyde 3079.2 ± 1.4 62.0 ± 1.5 54.9 ± 1.1 3-Thiophenecarboxaldehyde 3081.2 ± 1.4 60.0 ± 1.5 52.6 ± 1.2 3-Methyl-2-thiophenecarboxaldehyde 3722.2 ± 1.5 98.3 ± 1.7 57.7 ± 1.3 5-Methyl-2-thiophenecarboxaldehyde 3727.0 ± 1.5 93.5 ± 1.7 56.2 ± 1.2 5-Ethyl-2-thiophenecarboxaldehyde 4367.6 ± 1.8 132.3 ± 2.0 62.2 ± 1.3 The standard molar enthalpies of formation of the title compounds, in the gaseous phase, were derived through these experimental thermodynamic parameters and the results are interpreted in terms of structural effects and compared with structurally similar compounds.