Experimental and computational study on the thermochemistry of ethylpiperidines

The standard (p∘ = 0.1 MPa) massic energies of combustion in oxygen of 1-ethylpiperidine and 2-ethylpiperidine, both in the liquid phase, were measured at T = 298.15 K by static bomb calorimetry. These values were used to derive the standard molar enthalpies of combustion and the standard molar enthalpies of formation, in the condensed phase, for these compounds. Further, the standard molar enthalpies of vaporization, at T = 298.15 K, of these two ethylpiperidine isomers were determined by Calvet microcalorimetry. The combustion calorimetry results together with those from the Calvet microcalorimetry, were used to derive the standard molar enthalpies of formation, at T = 298.15 K, in the gaseous phase.-ΔcHm∘(l)/(kJ·mol-1)ΔlgHm∘/(kJ·mol-1)1-Ethylpiperidine4776.8 ± 1.639.44 ± 0.652-Ethylpiperidine4740.3 ± 1.548.22 ± 0.89Full-size tableTable optionsView in workspaceDownload as CSVIn parallel, theoretical calculations have been carried out for all the ethylpiperidine isomers, enabling the estimation of gas-phase enthalpies of formation for these compounds. The comparison with the present experimental data is very good and, thus, supports the quality of the results calculated for the 3-ethyl and 4-ethylpiperidines.