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Journal of Thermal Analysis and Calorimetry
Authors: G. Barone, C. Giancola, T. H. Lilley, C. A. Mattia, and R. Puliti

Enthalpies and temperatures of fusion or transition for four substituted dipeptides (Nacetylamides of glycyl-L-alanine (NAGAA),L-alanyl-L-alanine (NAA2A),L-prolyl-glycine (NAPGA) andL-leucyl-L-proline monohydrate (NALPA·H2O)) were determined by differential scanning calorimetry and the entropies of fusion derived. The results obtained have been compared with those of the corresponding substituted aminoacids and some of their racemic crystalline mixtures. The enthalpies and entropies of fusion of some substituted aminoacids have been redetermined. The results are discussed in comparison with crystal structural data, which has been reported in the literature or determined recently by some of the authors. Rationalization of the fusion parameters was attempted mainly on the basis of the number of intramolecular hydrogen bonds and the packing densities in the crystals.

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Crystal structures together with enthalpies and temperatures of fusion of two substituted amino acids, N-acetylsarcosinamide (NASarA) and N-acetyl-L-isoleucinamide (NAIA), were determined by single crystal X-ray analysis and differential scanning calorimetry, respectively. The results were compared with those of some analogous amino acid derivatives previously studied. The detailed knowledge of crystallographic parameters is undoubtedly useful for discussing the thermodynamic results and rationalizing the fusion behaviour, owing to the rather poor knowledge of the molecular interactions occurring in the melt.

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Abstract  

The present study reports a differential scanning calorimetry (DSC) study of the solid aldehydes: 4-hydroxybenzaldehyde [123-08-0] 1; 4-hydroxy-3-methoxybenzaldehyde (vanillin) [121-33-5] 2; 3-ethoxy-4-hydroxybenzaldehyde (ethyl vanillin) [121-32-4] 3; 3,4-dimethoxybenzaldehyde (veratraldehyde) [120-14-9] 4 and 4-methoxycinnamaldehyde [1963-36-6] 5, in the temperature interval from T=268 K to their respective melting temperatures. Temperatures, enthalpies and entropies of fusion and the heat capacities of the compounds as a function of temperature are reported.

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Abstract  

A previously established equation of a stoichiometric phase liquidus curve was applied to determination of the phase diagrams of the systems MIPO3-Pr(PO3)3 (with MI=Na, Rb, Cs or Ag). The temperature, enthalpy and entropy of fusion were calculated for each solid phase with the exception of silver polyphosphate, the crystallization field of which was very limited. The enthalpy of fusion of the polyphosphate Pr(PO3)3 was determined from the DTA curve. The melting enthalpy of Pr(PO3)3 calculated from the different binary systems was approximately equal to the measured value. The calculated temperatures and compositions were in good agreement with those determined experimentally.

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Journal of Thermal Analysis and Calorimetry
Authors: Manuel Temprado, Maria Roux, Archana Parameswar, Alexei Demchenko, James Chickos, and Joel Liebman

Abstract  

The present study reports a DSC study of the thio-and dithiocarbamates: 3H-benzoxazole-2-thione (2-mercaptobenzoxazole), 3H-benzothiazole-2-thione (2-mercaptobenzothiazole), thiazolidine-2-thione (2-mercapto-2-thiazoline), oxazolidine-2-thione (2-mercapto-2-oxazoline) and tetrahydro-1,3-oxazine-2-thione (5,6-dihydro-4H-1,3-oxazine-2-thiol) in the temperature interval T=268 K and the melting temperatures. Temperatures, enthalpies and entropies of fusion are reported. No solid-solid phase transitions were observed for the compounds in the temperature interval studied. The heat capacity of the compounds as a function of temperature was measured.

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Abstract  

The standard molar enthalpy of combustion of cholesterol was measured at constant volume. According to value of Δr U m θ(−14358.4±20.65 kJ mol−1), Δr H m θ(−14385.7 kJ mol−1) of combustion reaction and Δf H m θ(2812.9 kJ mol−1) of cholesterol were obtained from the reaction equation. The enthalpy of combustion reaction of cholesterol was also estimated by the average bond enthalpies. By design of a thermo-chemical recycle, the enthalpy of combustion of cholesterol were calculated between 283.15∼373.15 K. Besides, molar enthalpy and entropy of fusion of cholesterol was obtained by DSC technique.

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Abstract  

Thermodynamic exploration of solid-liquid equilibria of the MIPO3-Cu(PO3)2 (with MI=Li, Na, K, Rb, Cs, Ag, Tl) systems is carried out with a semi-empirical equation of the liquidus curves. The enthalpies of fusion of pure polyphosphates and some intermediate compounds were determined from DTA curves. The temperature, enthalpy and entropy of fusion are calculated for each solid phase with the exception of silver polyphosphate and the intermediate compound Cs4Cu(PO3)6 which have very limited crystallization fields. The calculated values of the melting enthalpies are approximately equal to the measured ones. The melting enthalpy of Cu(PO3)2 calculated from different binary systems shows a wide variation in the obtained values, 35-54 kJ mol-1. The experimental value is 33.65 kJ mol-1. The calculated temperatures and compositions in most binary systems are in good agreement with experimental determinations.

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Abstract  

The heat capacities of trans-(R)-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylic acid in the temperature range from 78 to 389 K were measured with a precise automatic adiabatic calorimeter. The sample was prepared with the purity of 0.9874 mole fraction. A solid-liquid fusion phase transition was observed in the experimental temperature range. The melting point, T m, enthalpy and entropy of fusion, Δfus H m, Δfus S m, were determined to be 344.75±0.02 K, 13.75±0.07 kJ mol−1, 39.88±0.21 J K−1 mol−1, respectively. The thermodynamic functions of the sample, H (T)-H (298.15), S (T)-S (298.15) and G (T)-G (298.15), were reported with a temperature interval of 5 K. The thermal decomposition of the sample was studied by TG analysis, the thermal decomposition starts at ca. 421 K and terminates at ca. 535 K, the maximum decomposition rate was obtained at 525 K. The order of reaction, pre-exponential factor and activation energy, are n=0.14, A=1.15·108 min−1, E=66.27 kJ mol−1, respectively.

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Abstract  

The low-temperature heat capacities of 1-hexadecanol have been measured with an automatic adiabatic calorimeter over the temperature range from 80 to 370 K. A solid-liquid phase transition was observed at T m=322.225±0.002 K and the molar enthalpy and entropy of fusion were determined to be 57.743±0.008 kJ mol−1 and 179.19±0.04 J K−1 mol−1, respectively. The purity, the real melting point (T 1) and the ideal melting point without any impurity or absolutely purity (T 0) of the sample under investigation were determined to be 99.162 mol%, 322.21 and 322.34 K, respectively, by fractional melting method. According to the polynomial equation of heat capacity and thermodynamic relationship, the thermodynamic functions of the compound relative to the reference temperature 298.15 K were calculated in the temperature ranges of 80 to 370 K with an interval of 5 K. In addition, further researches of thermal properties for this compound were carried out by means of TG/DTG.

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Abstract  

The solubility of two n-alkanes in commercial organic liquids, such as diesel fuel and jet fuel represent a problem to industry, because they precipitate in an unpredictable fashion. First we calculated the metastable enthalpy and entropy of fusion of the low temperature forms of the n-alkanes. We analyzed the solubility of alkanes n-C22H46, n-C23H48, n-C24H50 and n-C28H58 in ethylbenzene, m-xylene, n-heptane and gas oil. All systems seem to be close ideal, possibly with a slight positive deviation. We analyzed the solubility at constant temperature of the ternary system solvent C22H46-C24H50, C23H48-C24H50, C13H28-C16H34, C20H42-C22H46, C20H42-C24H50 and C20H42-C28H58, and looked at cloud points in various ternary systems. When the difference in the number of carbon atoms in the two alkanes is small, four or less, a metastable solid solution precipitates from the solvent. If the difference in the number of carbon atoms is six or more, the ‘equilibrium’ phases, or at least phases with low solubility precipitate.

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