ENERGETICS OF METHYLPIPERIDINES
Manuel A. V. Ribeiro da Silva, Joana I. T. A. Cabral and José R. B. Gomes
Centro de Investigação em Química, Department of Chemistry, Faculty of Science, University of Porto, R. Campo Alegre, 687,P-4169-007 Porto, Portugal
The standard (pº = 0.1 MPa) molar enthalpies of formation, in the gaseous phase of 1-methylpiperidine, 3-methylpiperidine and 4-methylpiperidine were derived from the standard molar enthalpies of combustion, determined by static bomb calorimetry, at T = 298.15 K, and the standard molar enthalpies of sublimation, measured using a high temperature Calvet Microcalorimeter.
In addition, and in order to be compared with the experimental results, theoretical calculations have been performed to determine for these compounds. The theoretical calculations were carried out considering the Møller-Plesset perturbation theory second-order correction to the Hartree-Fock energy, MP2, or the G3MP2B3 method based on the Gaussian-3 theory.
Table.- Experimental and theoretical (MP2/6-31G*) standard molar enthalpies of formation in gaseous phase for piperidine and methylpiperidines isomers, at T = 298.15 K.
Piperidine: (exptl: - 47.15 ± 0.63 [1]) [computed: -54.4(MP2) -48.2(G3MP2B3)] 1-Methylpiperidine: (exptl: - 59.2 ± 3.5) [computed: -59.8(MP2)] 2-Methylpiperidine: (exptl: - 84.5 ± 1.1 [1]) [computed: -85.9(MP2)] 3-Methylpiperidine: (exptl: - 79.5 ± 2.9) [computed: -78.6(MP2)] 4-Methylpiperidine: (exptl: - 82.7 ± 3.2) [computed: -79.1(MP2)][1] W. Good, J. Chem. Eng. Data 17, 28-31 (1972).
Thanks are due to Fundação para a Ciência e Tecnologia (FCT) for financial support given to Centro de Investigação em Química of University of Porto. J.I.T.A.C. and J.R.B.G. thank FCT for the award of a PhD (BD/5364/2001) and of a post-doc (BPD/11582/2002) research grants, respectively.