An examination of the vaporization enthalpies and vapor pressures of pyrazine, pyrimidine, pyridazine, and 1,3,5-triazine |
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Authors: | Dmitri Lipkind James S Chickos |
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Institution: | (1) Department of Chemistry and Biochemistry, University of Missouri-St. Louis, St. Louis, MO 63121, USA |
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Abstract: | The vaporization enthalpies and liquid vapor pressures from T = 298.15 K to T = 400 K of 1,3,5-triazine, pyrazine, pyrimidine, and pyridazine using pyridines and pyrazines as standards have been measured
by correlation-gas chromatography. The vaporization enthalpies of 1,3,5-triazine (38.8 ± 1.9 kJ mol−1) and pyrazine (40.5 ± 1.7 kJ mol−1) obtained by these correlations are in good agreement with current literature values. The value obtained for pyrimidine (41.0 ± 1.9 kJ mol−1) can be compared with a literature value of 50.0 kJ mol−1. Combined with the condensed phase enthalpy of formation in the literature, this results in a gas-phase enthalpy of formation,
Δf
H
m (g, 298.15 K), of 187.6 ± 2.2 kJ mol−1 for pyrimidine, compared to a value of 195.1 ± 2.1 calculated for pyrazine. Vapor pressures also obtained by correlation
are used to predict boiling temperatures (BT). Good agreement with experimental BT (±4.2 K) including results for pyrimidine
is observed for most compounds with the exception of the pyridazines. The results suggest that compounds containing one or
two nitrogen atoms in the ring are suitable standards for correlating various heterocyclic compounds provided the nitrogen
atoms are isolated from each other by carbon. Pyridazines do not appear to be evaluated correctly using pyridines and pyrazines
as standards. |
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Keywords: | Pyridine Pyrazine Pyrimidine Vaporization enthalpy Enthalpy of formation Vapor pressure |
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