Excess molar enthalpies of binary mixtures for (tributyl phosphate+methanol/ethanol) at 298.15 K

Excess molar enthalpies of binary mixtures for tributyl phosphate (TBP)+methanol/ethanol were measured with a TAM air Isothermal calorimeter at 298.15 K and ambient. The results for xTBP+(1–x)CH₃OH are negative in the whole range of composition, while the values for xTBP+(1–x)C₂H₅OH change from positive values at low x to small negative values at high x. The experimental results have been correlated with the Redlich–Kister polynomial. IR spectra of the mixtures were measured to investigate the effect of hydrogen bonding in the mixture.     

Enthalpies of mixing of <Emphasis Type="Italic">o</Emphasis>- and <Emphasis Type="Italic">m</Emphasis>-isomers at 298.15 K

Excess enthalpies (H ^E) of 17 binary mixtures of o- and m-isomers of dichlorobenzene, difluorobenzene, methoxymethylbenzene, dimethylbenzene, dimethoxybenzene, aminofluorobenzene, fluoronitrobenzene, diethylbenzene, chlorofluorobenzene, fluoroiodobenzene, bromofluorobenzene, chloromethylbenzene, fluoromethylbenzene, bromomethylbenzene, iodomethylbenzene, fluoromethoxybenzene, dibromobenzene at 298.15 K were measured. All excess enthalpies measured were very small, and those of o-+m-isomers of aminofluorobenzene, dibromobenzene and iodomethylbenzene were negative but 14 other binary mixtures of isomers were positive over the whole range of mole fractions. H ^E of o-+m-isomers of dimethoxybenzene showed the largest enthalpic instability and those of aminofluorobenzene showed the largest enthalpic stability. There was a correlation between dipole–dipole interaction, dipole–induced dipole interaction or entropies of vaporization and excess partial molar enthalpies at infinite dilution.     

Chromatographic study of the thermodynamics of solutions of hydrocarbons in liquid crystal solvents. Evidence for order disturbance by the solutes

Gas-chromatographic experiments were carried out in various phases of the solvents 4-acetoxy-N-[4-methoxy-benzylidene]-aniline, dibutoxyazoxybenzene, lithium stearate, dihexoxyazoxybenzene, and diheptoxyazoxybenzene. The solutes were linear, branched and cyclic alkanes, and substituted benzenes. Excess enthalpies, entropies, and free entropies were calculated from net retention volumes. In the nematic liquid crystalline phases the effect of order disturbance was significant in and but it was, by enthalpy-entropy compensation, not demonstrable in . Differences in flexibility and degree of expansion of the solutes did not result in significantly different values of the excess quantities.     

NMR and Excess Volumes Studies in DMF–Alcohol Mixtures

Chemical shifts of the alcohol and DMF protons in DMF–alcohol mixtures with the mole fraction of alcohol are reported in order to study the hydrogen bond interaction present in the mixtures. The densities of DMF–methanol mixture at 22°C are also measured. Excess volumes and excess chemical shifts are correlated by the Redlich–Kister equation. The relation between excess volumes and excess chemical shifts in the mixtures is discussed. It is found that the maximum excess chemical shifts ^E(CHO-OH) and ^E(CH₃-OH) are positioned at about mole fraction methanol = 0.57 for the DMF–methanol system, as is V ^E. The results show that the NMR spectral method offers a valuable approach to similar future studies of interactions in mixtures.     

Excess molar enthalpy of binary mixtures of hexane+ethyl benzene, <Emphasis Type="Italic">o</Emphasis>-xylene, <Emphasis Type="Italic">m</Emphasis>-xylene and <Emphasis Type="Italic">p</Emphasis>-xylene at 298.15 K

Summary This paper reports excess molar enthalpies of the binary systems hexane+ethyl benzene, hexane+o-xylene, hexane+m-xylene and hexane+p-xylene at 298.15 K and atmospheric pressure, over the whole composition range. The data was measured directly using a Calvet microcalorimeter. The excess magnitude was correlated to a Redlich-Kister type equation for each mixture. Also, we will discuss the results for the four mixtures studied here and by comparison with the same binary systems but containing propyl propanoate as first component. Finally, we will correlate our results with the Nitta-Chao and the three UNIFAC theoretical approximations.     

Thermodynamics of molecular interactions in ethyl iodide+toluene mixtures

The excess Gibb's free energy of mixing, G^E, for ethyl iodide+toluene at 25°C have been obtained from the measured vapor pressuure data. The H^E and G^E values for ethyl iodide+toluene are positive throughout the ethyl iodide concentration range and G^E>H^E. The results have been analyzed in terms of Flory and ideal associated model theory of nonelectrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AN and A₂B molecular species describes well (within±10 J-mol^–1 in the worst case) the general dependence of H^E on X_A (mole fraction of ethyl iodide) over the whole composition range for ethyl iodide+toluene mixtures. The equilibrium constants for A+A AB and 2A+BA₂B reactions along with the enthalpies of formation of AB and A₂B molecular species have been calculated.     

Excess enthalpies of ethylbenzene + alkane systems at 25°C. An interpretation in terms of the Prigogine-Flory-Patterson model

The molar excess enthalpies for the ethylbenzene + n-decane and ethylbenzene + n-tetradecane systems have been measured at 25°C over the complete concentration range. These results and others from the literature for alkanes + ethylbenzene, and alkanes + toluene have been discussed in terms of the Prigogine-Flory-Patterson theory.     

Volume and compressibility changes on mixing aqueous solutions of the amino acid and poly(ethylene glycol)

The volume and compressibility changes on mixing aqueous solutions of the amino acid and poly(ethylene glycol) were measured with a vibration densimeter and a sing-around velocimeter at 298.15 K. For the system of alanine-PEG-H₂O, the additivity rule for the mean apparent molal volume and compressibility at infinite dilution held, and the excess volume and compressibility changes on mixing were obtained. For the system of glycine-PEG-H₂O, the additivity rule for the mean apparent molal compressibility at infinite dilution did not hold. While the mean apparent molal volume and compressibility changes were negative and positive for the systems of another amino acid-PEG-H₂O, respectively, where amino acids were valine, isoleucine, leucine, phenylalanine, and tryptophan. These results suggest that glycine and alanine are excluded from the hydration layer around PEG chain and the amino acids with a larger side chain than alanine are bound to the PEG chain due to the hydrophobic interaction. The hydration number per monomer around PEG chain was estimated to be 3.9.     

Determination of Enantiomeric Excess of Glutamic Acids by Lab-made Capillary Array Electrophoresis

The techniques of combinatorial chemistry have recently been applied to the discovery of new asymmetric catalyst for a variety of organic transformations1-3. Using combina- torial methods, it is straightforward to generate thousands of potential asymmetri…     

Practical synthesis of 1-deoxy-d-xylulose and 1-deoxy-d-xylulose 5-phosphate allowing deuterium labelling

An optimised gram scale synthesis allows the production of 1-deoxy-d-xylulose and 1-deoxy-d-xylulose 5-phosphate with possible deuterium labelling at C-5. Such substrates are required for investigations on the mevalonate-independent 2-C-methyl-d-erythritol 4-phosphate pathway for isoprenoid biosynthesis in bacteria and chloroplasts of phototrophic eukaryotes and for the biosynthesis of vitamins B₁ (thiamine diphosphate) and B₆ (pyridoxol phosphate) in bacteria.