Thermochemical Study of Three Hindered Pyridine Derivatives

Abstract

The present work reports the values of the gaseous standard (p° = 0.1 MPa) molar enthalpy of formation of three pyridine derivatives substituted with one, two, and three tert-butyl groups, in positions para, ortho-ortho and ortho-para-ortho to the nitrogen, respectively. The standard molar energies of combustion of each compound, determined by static bomb calorimetry, yielded their standard molar enthalpies of formation in the condensed phase at T = 298.15 K, which together with the values of the standard molar enthalpies of vaporization or sublimation, measured by Calvet microcalorimetry, allowed the calculation of the standard gas phase molar enthalpy of formation of each compound studied. The enthalpies of combustion for 4-tert-butylpyridine (l), 2,6-di-tert-butylpyridine (l) and 2,4,6-tri-tert-butylpyridine (cr) were found to be, respectively, −(5 370.1 ± 3.4) kJ mol−1, −(7954.2 ± 4.0) kJ mol−1, and −(10 542.9 ± 4.9) kJ mol−1. The molar enthalpies of vaporization were measured as (54.4 ± 1.3) kJ mol−1...