Thermochemistry of 5,10,15,20-tetraphenylporphyrin

Abstract

Saturated vapor pressure of 5,10,15,20-tetraphenylporphyrin (TPP) was determined by Knudsen effusion mass spectrometry technique. The temperature dependence of the vapor pressure is described by the equation ln (p/Pa) = −(23.45 ± 0.26)⋅103/T + (37.32 ± 0.47) in the temperature range 490–615 K. The molar heat capacity measurements of TPP were performed in the temperature range 169–568 K. Quantum-chemical calculations of the structure and force field of the TPP molecule were carried out. These data were used to calculate thermodynamic functions of TPP in the solid and gas states. The enthalpy of sublimation of triclinic form of TPP was determined by the second and third laws of thermodynamics. The value ΔsH° (298.15 K) = 220 ± 12 kJ⋅mol−1 was recommended. The reaction based Feller-Peterson-Dixon approach predicts the gas phase TPP formation enthalpy ΔfH° (298.15 K) = 1004 ± 10 kJ⋅mol−1. A combination of the two last values results in the formation enthalpy of the TPP triclinic form ΔfH° (298.15 K) = 784 ± 15 kJ⋅mol−1.