The thermochemistry of 2,4-pentanedione revisited: Observance of a nonzero enthalpy of mixing between tautomers and its effects on enthalpies of formation
The enthalpies of formation of pure liquid and gas-phase (Z)-4-hydroxy-3-penten-2-one and 2,4-pentanedione are examined in the light of some more recent NMR studies on the enthalpy differences between gas-phase enthalpies of the two tautomers. Correlation gas chromatography experiments are used to e...
| Authors: | , , , , |
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| Format: | article |
| Status: | Versión enviada para evaluación y publicación |
| Publication Date: | 2005 |
| Country: | España |
| Institution: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repository: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/271813 |
| Online Access: | http://hdl.handle.net/10261/271813 |
| Access Level: | Open access |
| Keyword: | Enthalpy Equilibrium Gases Liquids Molecular structure |
| Summary: | The enthalpies of formation of pure liquid and gas-phase (Z)-4-hydroxy-3-penten-2-one and 2,4-pentanedione are examined in the light of some more recent NMR studies on the enthalpy differences between gas-phase enthalpies of the two tautomers. Correlation gas chromatography experiments are used to evaluate the vaporization enthalpies of the pure tautomers. Values of (51.2 ± 2.2) and (50.8 ± 0.6) kJ·mol-1 are measured for pure 2,4-pentanedione and (Z)-4-hydroxy-3-penten-2-one, respectively. The value of (50.8 ± 0.6) kJ·mol-1 can be contrasted to a value of (43.2 ± 0.2) kJ·mol-1 calculated for pure (Z)-4-hydroxy-3-penten-2-one when the vaporization enthalpy is measured in a mixture of tautomers. The difference is attributed to an endothermic enthalpy of mixing that destabilizes the mixture relative to the pure components. Calculation of new enthalpies of formation for (Z)-4-hydroxy-3-penten-2-one and 2,4-pentanedione in both the gas, ΔfH°m(g) = (−378.2 ± 1.2) and (−358.9 ± 2.5) kJ·mol-1, respectively, and liquid phases, ΔfH°m(l) = (−429.0 ± 1.0) and (−410.1 ± 1.2) kJ·mol-1, respectively, results in enthalpy differences between the two tautomers both in the liquid and gas phases that are identical within experimental error, and in excellent agreement with recent gas-phase NMR studies. |
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