Temprado Manuel, Roux Maria Victoria, Umnahanant Patamaporn, Zhao Hui, Chickos James S
Department of Chemistry and Biochemistry, University of Missouri-St. Louis, St. Louis, Missouri 63121, USA.
J Phys Chem B. 2005 Jun 30;109(25):12590-5. doi: 10.1021/jp0515131.
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, Delta(f)H degrees (m)(g) = (-378.2 +/- 1.2) and (-358.9 +/- 2.5) kJ.mol(-1), respectively, and liquid phases, Delta(f)H degrees (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.
鉴于最近一些关于两种互变异构体气相焓差的核磁共振研究，对纯液态和气态的(Z)-4-羟基-3-戊烯-2-酮和2,4-戊二酮的生成焓进行了研究。采用相关气相色谱实验来评估纯互变异构体的汽化焓。测得纯2,4-戊二酮和(Z)-4-羟基-3-戊烯-2-酮的汽化焓值分别为(51.2±2.2)和(50.8±0.6)kJ·mol⁻¹。当在互变异构体混合物中测量汽化焓时，纯(Z)-4-羟基-3-戊烯-2-酮计算值为(43.2±0.2)kJ·mol⁻¹，与之形成对比的是(50.8±0.6)kJ·mol⁻¹。这种差异归因于混合的吸热焓，它使混合物相对于纯组分不稳定。计算出(Z)-4-羟基-3-戊烯-2-酮和2,4-戊二酮在气相（ΔfH°(m)(g)分别为(-378.2±1.2)和(-358.9±2.5)kJ·mol⁻¹）和液相（ΔfH°(m)(l)分别为(-429.0±1.0)和(-410.1±1.2)kJ·mol⁻¹）中的新生成焓，结果表明两种互变异构体在液相和气相中的焓差在实验误差范围内相同，并且与最近的气相核磁共振研究结果高度一致。
