Experimental thermochemical study of the enthalpies of formation and sublimation of isonicotinamide, picolinamide, nicotinamide, isonicotinamideN-oxide, and nicotinamideN-oxide. The dissociation enthalpies of the N–O bonds

Abstract

The standard (p∘= 0.1MPa) molar enthalpies of combustion in oxygen, at T= 298.15 K, for crystalline picolinamide (2-NH2COPy), nicotinamide (3-NH2COPy), isonicotinamide (4-NH2COPy), nicotinamide N -oxide (3- NH2COPyNO), and isonicotinamide N - oxide (4-NH2COPyNO) were measured by static-bomb calorimetry. These values were used to derive the standard molar enthalpies of formation of the crystalline compounds. The standard molar enthalpies of sublimation, at T= 298.15 K, for the three pyridinecarboxamide isomers were measured by microcalorimetry and the standard molar enthalpies of sublimation for the two pyridinecarboxamide N -oxide compounds were measured by a mass-loss effusion technique. From the enthalpies of formation of the gaseous compounds, the molar dissociation enthalpies Dmoof the (N+– O−) covalent bonds were derived. Comparison has been made with Dmo(N–O) values in pyridine N -oxide derivatives.