Standard molar enthalpies of formation of some trichloroanilines by rotating-bomb calorimetry

The standard ( p^o =  0.1 MPa) molar enthalpies of formation Δ_fH_m^o, at the temperature 298.15 K, for crystalline 2,3,4-, 2,4,5-, 2,4,6- and 3,4,5-trichloroaniline were derived from the molar enthalpies of combustion Δ_cH_m^oin oxygen using rotating bomb combustion calorimetry. The reaction products were CO₂(g), N₂(g), and HCl · 600H₂O(l). The standard molar enthalpies of sublimation Δ_cr^gH_m^oat T =  298.15 K were measured by Calvet microcalorimetry. The results are as follows: The derived standard molar enthalpies of formation of the gaseous compounds were compared with values estimated by assuming the enthalpy increment for substitution of chlorine in aniline to be the same as for substitution into benzene.     

Limiting partial molar excess enthalpies by flow calorimetry: Some organic solvents in water

A Picker flow microcalorimeter was employed in conjunction with asymmetric syringe-type pumps to measure heats of mixing of highly dilute aqueous solutions of organic solvents. These data were used in turn to determine limiting partial molar excess enthalpies of the examined solvents in water. The measurements were carried out at 298.15 K for 29 common, oxygen and/or nitrogen containing solvents exhibiting complete miscibility with water. Except for only one compound, formamide, the limiting partial molar excess enthalpies are exothermic indicating that the process of dissolution is energetically favored. Comparison to literature data (in most cases to solution enthalpies at infinite dilution measured by batch calorimetry) proved the technique applied to be sufficiently accurate.     

Calculations of the enthalpies of combustion of organic compounds by the additive scheme

The enthalpies of combustion of more than 200 organic compounds were analyzed. Group contributions to Δ_c H ^o were calculated and used to estimate the enthalpies of combustion of a wide range of organic substances of various classes.

     

Investigations of solid phase transitions of low molecular organic compounds by differential scanning calorimetry

For the purpose of finding temperature standards for DTA at the temperature below 150°, some solid transitions of low molecular organic compounds were measured by differential scanning calorimetry. Among fourteen materials, we have concluded to select transitions for hexachloroethane (71°) and hexamethylbenzene (110°) as candidates for such standards.

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Zusammenfassung Zur Temperaturnormung unter 150° die DTA Methode wurden verschiedene organische Verbindungen von niedrigem Molekulargewicht und geeigneten Umwandlungen in fester Phase durch Differential Scanning Kalorimetrie geprüft. Von 14 verschiedenen Substanzen wurden Hexachloräthan (71°) und Hexamethylbenzol (110°) zum gesuchten Zweck geeignet gefunden.

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Résumé Pour le but de trouver des étalons de température au-dessous de 150°C pour l'ATD, on a examiné les transitions en phase solide de différents composés organiques de bas poids moléculaire à l'aide d'un analyseur enthalpique différentiel. Sur les 14 échantillons étudiés, on propose l'hexachloroéthane (71°) et l'hexaméthylbenzène (110°) comme étalons.

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150° . , 14 (71°) (110°), .

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The authors wish to thank Dr. H. G. McAdie of the Ontario Research Foundation, Canada, for his kind suggestions on this work.     

Relative electronegativities of germanium and silicon in organic compounds

Summary On the basis of a study of the relative reactivities of analogous carbofunctional compounds of germanium and silicon it is concluded that in these compounds germanium is more electronegative than silicon.We thank L. A. Leites for carrying out the spectroscopic analysis and A. A. Bugorkova for determining the kinetics of the reaction of (CH₃)₃GeCH₂Cl with KI.     

Calculation of some thermodynamic properties of air plasmas: Internal partition functions,plasma composition,and thermodynamic functions

The thermodynamic properties of air plasmas are calculated in the framework of the C.L.T.E. hypothesis, for pressures varying from 1 to 200 atm, in a temperature range from 1000 to 30,000 K. In these calculations, the neutral mon--, di-, and triatomic species, as well as their positive and negative ions, are taken into account. From the internal partition function values, the plasma compositions and the thermodynamic functions (specific enthalpy, Gibbs and Helmholtz free energies and entropy) are calculated.     

Direct observation of hydrophobic interactions in aqueous solutions of organic compounds by supercooling and enthalpies of mixing

Supercooling temperatures and enthalpies of mixing with some solvents have been examined for two kinds of solutions subjected to different thermal treatments (solutions I and II) of tetrahydrofuran (THF), isopropyl alcohol (2-PrOH), and ethyleneglycol butylether (BE), and ethyleneglycol isobutylether (i-BE) in order to observe more directly the structural organization of water molecules around a nonpolar molecule in an aqueous solution. For THF and 2-PrOH solutions, supercooling temperatures of solution I were found to be 2–3 degrees higher than those of solution II, and differences H_I-H_II were found to be about 3 kJ mol^–1. It has been concluded that these results directly reflect the difference in the stability of hydrogen-bonded water networks in an aqueous solution.     

Relative kinetic stability towards redox decomposition of cerium(IV) complexes with some organic compounds

Monatshefte für Chemie - Chemical Monthly - A comparative analysis is performed on the stability constants $${upbeta }_{1yn}$$ and intramolecular redox decomposition rate constants $$k_{n; =...     

Standard molar enthalpies of formation of KCdCl3 and K4CdCl6 by high-temperature drop calorimetry

Enthalpies of the synthesis reactions of the two compounds KCdCl₃(cr) and K₄CdCl₆(cr) from KCl(cr) and CdCl₂(cr) have been measured by drop calorimetry of solid samples of KCl, CdCl₂, KCdCl₃, and K₄CdCl₆ into melted mixtures of KCl and CdCl₂. For the two reactions: (1), CdCl₂(cr)+KCl(cr) = KCdCl₃(cr); and (2), CdCl₂(cr)+4KCl(cr) = K₄CdCl₆(cr), the experiments lead to the two standard molar enthalpies of reaction at 298.15 K: Δ₁H_m^o = ?(21.7±1.0) kJ·mol^?1 and Δ₂H_m^o = ?(39.0±3.8) kJ·mol^?1. These values are not in good agreement with those of previous workers.     

Solubility of KF in four organic solvents and thermodynamic dissolution functions

The solubilities of potassium fluoride (KF) in protic and aprotic polar solvents (N,N-dimethylethanolamine, diethanolamine, pyridine, and sulfolane) were measured at temperatures ranging from 308.73 to 367.37 K, and the data were correlated using the modified Apelblat equation. The dissolution enthalpy and dissolution entropy were calculated from the solubility data. The interactions between solute and solvent were discussed. The data obtained can be helpful in the search of optimal ways of preparation of 2,3,4,5-tetrafluorobenzoic acid.     

Accurate prediction of enthalpies of formation for a large set of organic compounds

This article describes a multiparameter calibration model, which improves the accuracy of density functional theory (DFT) for the prediction of standard enthalpies of formation for a large set of organic compounds. The model applies atom based, bond based, electronic, and radical environmental correction terms to calibrate the calculated enthalpies of formation at B3LYP/6‐31G(d,p) level by a least‐square method. A diverse data set of 771 closed‐shell compounds and radicals is used to train the model. The leave‐one‐out cross validation squared correlation coefficient q² of 0.84 and squared correlation coefficient r² of 0.86 for the final model are obtained. The meanabsolute error in enthalpies of formation for the dataset is reduced from 4.9 kcal/mol before calibration to 2.1 kcal/mol after calibration. Five‐fold cross validation is also used to estimate the performance of the calibration model and similar results are obtained. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

The heat capacities and thermodynamic functions of some derivatives of ferrocene

The heat capacities of benzoylferrocene (BOF), C₅H₅FeC₅H₄COC₆H₅, and benzylferrocene (BF), C₅H₅FeC₅H₄CH₂C₆H₅, have been measured by the low-temperature adiabatic calorimetry in the temperature range from 6 K to 372 K. The purity benzylferrocene and thermodynamic properties – the triple point temperature and the enthalpy of fusion have been obtained. The ideal gas thermodynamic functions (changes of the entropy, enthalpy, and Gibbs free energy) of BOF and BF were derived at T = 298.15 K using the heat capacities and previously determined data on the saturation vapours pressures and the enthalpies of sublimation. The ideal gas enthalpy of formation and absolute entropy of BOF at T = 298.15 K have been obtained from quantum chemical calculations, where as the thermodynamic properties of BF have been estimated by empirical method of group equations. A good agreement between experimental and theoretical values provides an additional check of the reliability of the experimental data.     

Molecular enthalpies: 1. Ground-state thermodynamic and computed enthalpies of the norbornadiene cycle

The enthalpies of formation of norbornadiene, norbornene, norbornane, nortricyclane, and quadricyclane, which are experimentally known, have been calculated using the semiempirical programs MNDO, AM1, and PM3 and the empirical force-field method MMP2. MMP2 agrees most closely with experimental results. Of the semiempirical methods, PM3 agrees most closely with experimental results and is very good for the alkenes. Enthalpies of hydrogenation, calculable fromH _f, are inconclusive on the question of ground-state homoaromatic stabilization of norbornadiene.