Thermochemistry of 2,2'-dipyridil N-oxide and 2,2'-dipyridil N,N'-dioxide. The dissociation enthalpies of the N-O bonds

Research highlights: → The standard enthalpies of formation of two crystalline 2,2'-dipyridil N-oxides were measured by combustion calorimetry. → The standard enthalpies of sublimation of two 2,2'-dipyridil N-oxides were derived from Knudsen effusion experiments. → First, second and mean (N-O) bond dissociation enthalpies (BDEs) for 2,2'-dipyridil N,N'-dioxide were derived. → The (N-O) bond dissociation enthalpy (BDE) for 2,2'-dipyridil N-oxide was calculated. - Abstract: In this paper, the first, second and mean (N-O) bond dissociation enthalpies (BDEs) were derived from the standard (po = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, ΔfHm0(g), at T = 298.15 K, of 2,2'-dipyridil N-oxide and 2,2'-dipyridil N,N'-dioxide. These values were calculated from experimental thermodynamic parameters, namely from the standard (po = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, ΔfHm0(cr), at T = 298.15 K, obtained from the standard molar enthalpies of combustion, ΔcHm0, measured by static bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from Knudsen mass-loss effusion method.