Low-temperature heat capacity and standard molar enthalpy of formation of crystalline 2-pyridinealdoxime (C 6H 6N 2O)

Abstract

The thermodynamic properties of 2-pyridinealdoxime were investigated through the thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). Low-temperature heat capacity C p,m of 2-pyridinealdoxime (C 6H 6N 2O; CAS 873-69-8) was measured in the temperature range from (80 to 373) K with a high precision automated adiabatic calorimeter. No phase transition or thermal anomaly was observed in this range. The thermodynamic functions [ H T − H 298.15] and [ S T − S 298.15] were calculated in the range from (80 to 375) K. The constant-volume energy and standard molar enthalpy of combustion have been determined, Δ c U ( C 6 H 6 N 2 O,cr ) = Δ c H m ∘ (C 6H 6N 2O, cr) = − (3297.11 ± 1.53) kJ · mol −1 (based on Δ n being zero in reaction of the combustion), 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, Δ f H m ∘ (C 6H 6N 2O, cr) = (78.56 ± 2.43) kJ · mol −1, from the standard molar enthalpy of combustion in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.