Thermodynamic properties and tautomerism of tetrazole

• Published in: The Journal of chemical thermodynamics Vol. 25; no. 4; pp. 485 - 493
• Main Authors: Kabo, G.J., Kozyro, A.A., Krasulin, A.P., Sevruk, V.M., Ivashkevich, L.S.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.04.1993; Elsevier
• Subjects: Chemical thermodynamics; Chemistry; Elements, mineral and organic compounds; Exact sciences and technology; General and physical chemistry; Thermodynamic properties; Knudsen effusion; Crystalline phase; Five membered ring; Temperature; Vapor pressure; Nitrogen heterocycle; Heat of sublimation; Enthalpy; Heat capacity; Free enthalpy; Entropy; Tautomerism; Microcalorimetry; Heat of fusion; Experimental study; Adiabatic calorimeter; Tetrazole; Gas phase; Thermodynamic properties; Organic compounds
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1006/jcht.1993.1156

The results of a study of tetrazole in different phase states are given. The heat capacity of crystalline tetrazole was measured by vacuum adiabatic calorimetry ( T = 5 K to 320 K) and by the triple-heat-bridge method ( T = 320 K to 400 K). The fusion properties: T fus = (430±1) K and Δ fus H o m = (18.0±0.5) kJ·mol -1 were obtained by the latter method. The C p . m = f( T) curve shows a small anomaly at temperatures from 230 to 245 K, connected with a reversible solid-to-solid transition: Δ trs H m = (14.0±1.0) J·mol -1 and Δ trs S m = (0.060±0.004) J·K -1·mol -1. The value of Δ f G o m(cr, 298.15 K) = (363.16±0.91) kJ·mol -1 was found on the basis of our own and literature results. The sublimation enthalpy was directly determined by heat-conduction differential microcalorimetry: Δ sub H o m(353 K) = (88.16±0.48) kJ· -1. The saturated vapour pressure of crystalline tetrazole was measured by the integral-effusion-Knudsen method from 333 K to 404 K: In( p/Pa) = (31.148±0.458)-(10560±168)(K/ T) and molar enthalpy of sublimation was calculated Δ sub H o m(369 K) = (87.80±1.40) kJ·mol -1. From these results a weight-averaged molar enthalpy of sublimation Δ sub H o m(350 K) = (88.25±0.45) kJ·mol -1 was calculated and the conventional molar entropy of gaseous tetrazole S o m (g, 350 K) = (274.07±1.45) J·K -1·mol -1 was found. The ideal-gas entropy of tetrazole was calculated by a statistical-mechanical method from molecular spectral quantities. The calculated entropy S o m (g, 350 K) = 277.52 J·K -1 is in satisfactory accordance with the experimental value. So, our thermodynamic investigation shows that tetrazole in the gas phase exist most probably as molecules with a single configuration (without a probable tautomerism 1-H = 2-H). Thermodynamic functions of tetrazole in the solid state ( T = 0 to 400 K) and in the ideal-gas state ( T = 100 K to 1000 K) were calculated and tabulated. The molar values C o p. m , Δ T O S o m, Δ T O H o m/ T, and Φ o m of crystalline and gaseous tetrazole at the temperature 298.15 K are, respectively: (76.52±0.31 and 52.37; 96.40±0.41 and 267.12; 45.60±0.18 and 37.77; and 50.80±0.45 and 229.35) J·K -1·mol -1.