ENTHALPIES OF COMBUSTION OF THE PYRIDINE N-OXIDE DERIVATIVES - 4-METHYL-PYRIDINE N-OXIDE, 3-CYANO-PYRIDINE N-OXIDE, 4-CYANO-PYRIDINE N-OXIDE, 3-HYDROXY-PYRIDINE N-OXIDE, 2-CARBOXY-PYRIDINE N-OXIDE, 4-CARBOXY-PYRIDINE N-OXIDE, AND 3-METHYL-4-NITRO, AND OF THE PYRIDINE-DERIVATIVES- 2-CARBOXY-PYRIDINE, AND 4-CARBOXY-PYRIDINE - THE DISSOCIATION ENTHALPIES OF THE N-O BONDS

The standard (p degrees = 0.1 MPa) molar enthalpies of formation Delta (f)H(m)degrees(cr) at T = 298.15 K were determined using static-bomb c alorimetry for crystalline 4-methylpyridine N-oxide (4MePyNO), 3-cyano pyridine N-oxide (3CNPyNO), 4-cyanopyridine N-oxide (4CNPyNO), 3-hydro xypyridine N-oxide (3OHPyNO), 2-pyridinecarboxylic acid N-oxide (2CO(2 )HpyNO), 4-pyridinecarboxylic acid N-oxide (4CO(2)HPyNO), 3-methyl-4-n itropyridine N-oxide (3Me4NO(2)PyNO), 2-pyridinecarboxylic acid (2CO(2 )HPy), and 4-pyridinecarboxylic acid (4CO(2)HPy). The standard molar e nthalpies of sublimation Delta(c)(rg) H(m)degrees at T = 298.15 K were measured by microcalorimetry, or by a mass-loss effusion technique, a nd from the enthalpies of formation of the gaseous compounds the disso ciation enthalpies D(m)degrees of the (N+-O-) dative covalent bonds we re derived. [GRAPHICS] Comparison has been made with D(m)degrees(N-O) values in pyridine N-oxide derivatives. (C) 1998 Academic Press.