Enthalpies of combustion of 4-nitropyridineN-oxide and pyridine-3-carboxylic acidN-oxide: the dissociation enthalpies of the N—O bonds in pyridineN-oxide derivatives

✍ Scribed by W.E. Acree Jr.; Sheryl A. Tucker; Maria D.M.C. Ribeiro da Silva; M. Agostinha R. Matos; J.M. Gonçalves; M.A.V. Ribeiro da Silva; G. Pilcher

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 369 KB
• Volume: 27
• Category: Article
• ISSN: 0021-9614
• DOI: 10.1006/jcht.1995.0038

✦ Synopsis

The standard (p°= 0.1 MPa) enthalpies of combustion at the temperature T = 298.15 K were measured by static-bomb calorimetry for crystalline 4-nitropyridine N-oxide and for pyridine-3-carboxylic acid N-oxide. The standard enthalpies of sublimation at T = 298.15 K were measured for 4-nitropyridine N-oxide by microcalorimetry and for pyridine-3-carboxylic acid N-oxide by a mass-loss effusion technique.

-DcH°m(cr)/(kJ•mol -1 ) D g cr H°m/(kJ•mol -1 ) 4-O2N-c-C5H4NO 2556.3 2 0.5 108.9 2 0.3 3-HO2C-c-C5H4NO 2698.2 2 0.7 152.3 2 1.9

From the standard molar enthalpies of formation of the gaseous compounds, the molar dissociation enthalpies of the (N-O) bonds were derived: D(N-O)/(kJ•mol -1 ) in 4-O2N-c-C5H4NO, 258.5 2 5.3; in 3-HO2C-c-C5H4NO, 252.8 2 2.7. The standard molar enthalpies of sublimation of 2-H3C-c-C5H4NO and 3-H3C-c-C5H4NO were measured by microcalorimetry: (78.2 2 2.2) kJ•mol -1 and (82.2 2 2.4) kJ•mol -1 , respectively, permitting the comparison of D(N-O) values in several pyridine N-oxide derivatives.