Phase relations in the system (chromium + rhodium + oxygen) and thermodynamic properties of CrRhO3

Phase relations in the system (chromium + rhodium + oxygen) at T = 1273 K have been determined by examination of equilibrated samples by optical and scanning electron microscopy, powder X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). Only one ternary oxide, CrRhO₃ with rhombohedral structure ($R\overline{3}$, a = 0.5031, and c = 1.3767 nm) has been identified. Alloys and the intermetallics along the (chromium + rhodium) binary were in equilibrium with Cr₂O₃. The thermodynamic properties of the CrRhO₃ have been determined in the temperature range (900 to 1300) K by using a solid-state electrochemical cell incorporating calcia-stabilized zirconia as the electrolyte. For the reaction,$\begin{array}{cc}\hfill & 1/2{\text{Cr}}_2{\text{O}}_3(\text{solid})+1/2{\text{Rh}}_2{\text{O}}_3(\text{solid})\to {\text{CrRhO}}_3(\text{solid})\text{,}\hfill \\ \hfill & \mathrm{\Delta }{G}^{°}\pm 140/(\text{J}·{\text{mol}}^{-1})=-31967+5.418(T/\text{K})\text{,}\hfill \end{array}$where Cr₂O₃ has the corundum structure and Rh₂O₃ has the orthorhombic structure. Thermodynamic properties of CrRhO₃ at T = 298.15 K have been evaluated. The compound decomposes on heating to a mixture of Cr₂O₃-rich sesquioxide solid solution, Rh, and O₂. The calculated decomposition temperatures are T = 1567 ± 5 K in pure O₂ and T = 1470 ± 5 K in air at a total pressure p^° = 0.1 MPa. The temperature-composition phase diagrams for the system (chromium + rhodium + oxygen) at different partial pressures of oxygen and an oxygen potential diagram at T = 1273 K are calculated from the thermodynamic information.     

A thermodynamic study of ketoreductase-catalyzed reactions 4. Reduction of 2-substituted cyclohexanones in n-hexane

The equilibrium constants K for the ketoreductase-catalyzed reduction reactions (2-substituted cyclohexanone + 2-propanol = cis- and trans-2-substituted cyclohexanol + acetone) have been measured in n-hexane as solvent. The 2-substituted cyclohexanones included in this study are: 2-methylcyclohexanone, 2-phenylcyclohexanone, and 2-benzylcyclohexanone. The equilibrium constants K for the reactions with 2-methylcyclohexanone were measured over the range T = 288.15 to 308.05 K. The thermodynamic quantities at T = 298.15 K are: K = (2.13 ± 0.06); ${\mathrm{\Delta }}_{\text{r}}{G}_{\text{m}}^{\circ }=-(1.87\pm 0.06)\text{kJ}·{\text{mol}}^{-1}$; ${\mathrm{\Delta }}_{\text{r}}{H}_{\text{m}}^{\circ }=-(6.56\pm 2.68)\text{kJ}·{\text{mol}}^{-1}$; and ${\mathrm{\Delta }}_{\text{r}}{S}_{\text{m}}^{\circ }=-(15.7\pm 9.2)\text{J}·{\text{K}}^{-1}·{\text{mol}}^{-1}$ for the reaction involving cis-2-methylcyclohexanol, and K = (10.7 ± 0.2); ${\mathrm{\Delta }}_{\text{r}}{G}_{\text{m}}^{\circ }=-(5.87\pm 0.04)\text{kJ}·{\text{mol}}^{-1}$; ${\mathrm{\Delta }}_{\text{r}}{H}_{\text{m}}^{\circ }=-(2.54\pm 1.8)\text{kJ}·{\text{mol}}^{-1}$; and ${\mathrm{\Delta }}_{\text{r}}{S}_{\text{m}}^{\circ }=(11.2\pm 6.4)\text{J}·{\text{K}}^{-1}·{\text{mol}}^{-1}$ for the reaction involving trans-2-methylcyclohexanol. The standard molar Gibbs free energy changes ${\mathrm{\Delta }}_{\text{r}}{G}_{\text{m}}^{\circ }$ for the reactions (trans-2-substituted cyclohexanol = cis-2-substituted cyclohexanol) in n-hexane have also been calculated and compared with the literature data that pertain to reactions in the gas phase and at higher temperatures. Experiments carried out with a chiral column demonstrated that the enzymatic reduction of 2-phenylcyclohexanone catalyzed by the ketoreductase used in this study is not stereoselective.     

When theory and experiment hold hands: The thermochemistry of γ-pyrone derivatives

In this work, we have determined the experimental standard $(p^{°}=0.1\text{MPa})$ molar enthalpies of formation, in the gas phase, of 2,6-dimethyl-4-pyrone ?(261.5 ± 2.6) kJ · mol^?1 and 2-ethyl-3-hydroxy-4-pyrone ?(420.9 ± 2.8) kJ · mol^?1. These values were obtained by combining the standard molar enthalpy of formation in the condensed phase, derived from combustion experiments in oxygen, at T = 298.15 K, in a static bomb calorimeter, with the standard molar enthalpy of sublimation, at T = 298.15 K, obtained by Calvet microcalorimetry. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets have been performed for these two compounds. Good agreement was obtained between the experimental and computational results. Using the same methodology, we calculated the standard molar enthalpy of formation of gaseous 2-methyl-3-hydroxy-4-pyrone.     

Molecular energetics of 4-methyldibenzothiophene: An experimental study

The standard ($p^{°}=0.1\text{MPa}$) molar enthalpy of formation of 4-methyldibenzothiophene, in the gaseous phase, at T = 298.15 K, was derived from the combination of the values of the standard molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, and the standard molar enthalpy of sublimation, at the same temperature. The standard molar enthalpy of formation in the crystalline phase, determined from the standard massic energy of combustion, in oxygen, is (70.9 ± 4.8) kJ · mol^?1 and was measured by rotating-bomb combustion calorimetry. From Calvet microcalorimetry measurements, the standard molar enthalpy of sublimation obtained is (90.3 ± 0.7) kJ · mol^?1.