Thermodynamic studies of crystalline 2-amino-5-nitropyridine (C5H5N3O2)

Low-temperature heat capacity Cp,m of 2-amino-5-nitropyridine (C5H5N3O2; CAS 4214-76-0) was measured in the temperature range from 80 to 396 K with a high precision automated adiabatic calorimeter. No phase transition or thermal anomaly was observed in this range. The thermodynamic functions [HT − H298.15] and [ST − S298.15] were calculated in the range from 80 to 395 K based on the heat capacity data. The standard molar energy and standard molar enthalpy of combustion have been determined, ΔcU (C5H5N3O2, s) = −(2676.26 ± 0.24) kJ mol−1 and ΔcHm° (C5H5N3O2, s) = −(2673.16 ± 0.24) kJ mol−1, by means of a precision oxygen-bomb combustion calorimeter at T = 298.15 ± 0.001 K. The standard molar enthalpy of formation has been derived, ΔfHm° (C5H5N3O2, s) = −(8.97 ± 0.99) kJ mol−1, from the standard molar enthalpy of combustion in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle. The thermodynamic properties were further investigated through differential scanning calorimeter (DSC) and the thermogravimetric (TG) analysis.