FePO4/SiO2 catalysts for propylene glycol oxidation

FePО4/SiO2 supported catalysts with a different content of iron phosphate are prepared. The properties of the catalyst are changed by the introduction of alkali metal compounds (Na or Cs) on its surface. The samples obtained are characterized by X-ray diffraction, low-temperature nitrogen adsorption, temperatureprogrammed reduction by hydrogen, and temperature-programmed desorption of ammonia. The catalytic properties are investigated in the reaction of gas-phase propylene glycol oxidation. It is shown that the selectivity of methylglyoxal formation on the unmodified catalysts is determined by the state of the supported active component and by its reduction–oxidation ability under the action of a reaction mixture

Assessment of Gaussian-3X theory for chlorinated organic molecules. Enthalpies of formation of chlorobenzenes and predictions for polychlorinated aromatic compounds

Dorofeeva OV, Vishnevskiy YV, Moiseeva NF. Assessment of Gaussian-3X theory for chlorinated organic molecules. Enthalpies of formation of chlorobenzenes and predictions for polychlorinated aromatic compounds. Structural Chemistry. 2006;17(4):383-392

Use of G4 Theory for the Assessment of Inaccuracies in Experimental Enthalpies of Formation of Aromatic Nitro Compounds

The gas-phase enthalpies of formation (Δ_f<i>H</i>₂₉₈^°) of 101 aromatic nitro compounds were calculated using the Gaussian-4 (G4) theory applied to the atomization and isodesmic reaction energies. The Δ_f<i>H</i>₂₉₈^° (g) values calculated from the atomization reactions were underestimated by an average of 13 kJ·mol^–1 and they could not be used for the assessment of inaccuracies in the experimental enthalpies of formation. A good agreement with the most available experimental data was obtained using the isodesmic reaction procedure. From 5 to 26 isodesmic reactions with different reference species were constructed for each compound. About 15 aliphatic nitro compounds and 100 different C/H/N/O/Cl compounds were used as the reference species in these reactions; the accuracy of enthalpies of formation of all reference compounds was preliminarily confirmed by theoretical calculations. Evidence of accuracy of experimental data was provided by the agreement with calculated values. The differences between the calculated and the experimental enthalpies of formation in the range from (8 to 46) kJ·mol^–1 were assigned to possible errors in the experimental values for 21 compounds. The theoretical Δ_f<i>H</i>₂₉₈^° (g) values were recommended for these compounds as being more reliable than the experimental values. On the basis of theoretical results, a reference data set of internally consistent gas-phase enthalpies of formation of aromatic nitro compounds was provided. Both experimental and calculated values are included in this data set. The recommended Δ_f<i>H</i>₂₉₈^° (g) values of aromatic nitro compounds are consistent with each other and with Δ_f<i>H</i>₂₉₈^° (g) values of about 115 different C/H/N/O/Cl compounds including aliphatic nitro compounds. More accurate condensed phase enthalpies of formation and enthalpies of sublimation (or vaporization) were recommended in some cases based on a critical analysis of reported experimental data supplemented by quantum chemical calculations

Gas-Phase Enthalpies of Formation and Enthalpies of Sublimation of Amino Acids Based on Isodesmic Reaction Calculations

Accurate gas-phase enthalpies of formation (Δ_f<i>H</i>₂₉₈^°) of 20 common α-amino acids, seven uncommon amino acids, and three small peptides were calculated by combining G4 theory calculations with an isodesmic reaction approach. The internal consistency over a set of Δ_f<i>H</i>₂₉₈^°(g) values was achieved by sequential adjustment of their values through the isodesmic reactions. Four amino acids, alanine, β-alanine, sarcosine, and glycine, with reliable internally self-consistent experimental data, were chosen as the key reference compounds. These amino acids together with about 100 compounds with reliable experimental data (their accuracy was supported by G4 calculations) were used to estimate the enthalpies of formation of remaining amino acids. All of the amino acids with the previously established enthalpies of formation were later used as the reference species in the isodesmic reactions for the other amino acids. A systematic comparison was made of 14 experimentally determined enthalpies of formation with the results of calculations. The experimental enthalpies of formation for 10 amino acids were reproduced with good accuracy, but the experimental and calculated values for 4 compounds differed by 11–21 kJ/mol. For these species, the theoretical Δ_f<i>H</i>₂₉₈^°(g) values were suggested as more reliable than the experimental values. On the basis of theoretical results, the recommended values for the gas-phase enthalpies of formation were also provided for amino acids for which the experimental Δ_f<i>H</i>₂₉₈^°(g) were not available. The enthalpies of sublimation were evaluated for all compounds by taking into account the literature data on the solid-phase enthalpies of formation and the Δ_f<i>H</i>₂₉₈^°(g) values recommended in our work. A special attention was paid to the accurate prediction of enthalpies of formation of amino acids from the atomization reactions. The problems associated with conformational flexibility of these compounds and harmonic treatment of low frequency torsional modes were discussed. The surprisingly good agreement between the Δ_f<i>H</i>₂₉₈^°(g) values calculated from the atomization and isodesmic reactions is largely the result of a fortuitous mutual compensation of various corrections used in the atomization reaction procedure