Experimental thermochemical study of 3-acetyl-2-methyl-5-phenylthiophene

Abstract

The standard ( p ∘ = 0.1 MPa ) massic energy of combustion, in oxygen, of the crystalline 3-acetyl-2-methyl-5-phenylthiophene was measured, at T = 298.15 K, by rotating-bomb combustion calorimetry, from which the standard molar enthalpy of formation, in the condensed phase, was calculated as Δ f H m ∘ ( cr ) = - ( 104.3 ± 3.1 ) kJ · mol - 1 . The corresponding standard molar enthalpy of sublimation, at T = 298.15 K, Δ cr g H m ∘ = ( 108.9 ± 0.4 ) kJ · mol - 1 , was derived by the Clausius–Clapeyron equation, from the temperature dependence of the vapour pressures of this compound, measured by the Knudsen effusion mass-loss technique. From the results presented above, the standard molar enthalpy of formation, in the gaseous phase, at T = 298.15 K, was derived, Δ f H m ∘ ( g ) = ( 4.6 ± 3.1 ) kJ · mol - 1 . This value, in conjunction with the literature values of the experimental enthalpies of formation of thiophene, 2-methylthiophene, and 3-acetylthiophene, was used to predict the enthalpic increment due to the introduction of a phenyl group in the position 2- of the thiophene ring. The calculated increment was compared with the corresponding ones in benzene and pyridine derivatives.