Thermochemistry of methoxythiophenes: Measurement of their enthalpies of vaporization and estimation of their enthalpies of formation in the condensed phase

•The enthalpies of vaporization of 2- and 3-methoxythiophenes have been measured by the transpiration method.•We have estimated the enthalpies of formation of methoxythiophenes in liquid phase.•The optimized geometries of methoxythiophenes have been tabulated and compared with the experimental crystal structures. Enthalpies of vaporization of 2- and 3-methoxythiophenes (48.32±0.30 and 48.54±0.22kJ·mol−1, respectively) have been measured by the transpiration method using nitrogen as the carrying and protecting stream. Combustion experiments leading to enthalpies of formation in the liquid phase, ΔfH0m(l), for both isomers failed due to rapid darkening of freshly distilled samples even under a protecting atmosphere. However, combination of experimental vaporization enthalpies with values of the gaseous enthalpies of formation, ΔfH0m(g), obtained by quantum-chemical calculations from our previous work Notario et al. (2012) [24] permits establishing estimated ΔfH0m(l) values of −(68.3±4.2) and −(80.1±4.2)kJ·mol−1, for 2- and 3-methoxythiophene, respectively.