Molecular interactions in poly(ethylene glycol)-water mixtures at various temperatures: density and isentropic compressibility study.

The densities and sound velocities of mixtures of water with poly(ethylene glycol), poly(ethylene glycol) monomethylether, and poly(ethylene glycol) dimethylether with mean molar weights between 250 and 500 have been measured as a function of mixture composition and temperature between 10 and 40 degrees C. Isentropic compressibilities are derived from the data and are compared to those for the ethylene glycol/water system and for other organic solvent/water mixtures. Relative minima in the mixture volume to ideal volume ratio and in the dependence of the compressibility upon mixture composition are discussed in terms of the conformational variability of the chainlike oligomers, of hydrogen-bonded networks, and of water clusters between the oligomer chains.     

Quantum chemical calculation of cation interaction with water molecules and ethylene glycol

A computer modeling is carried out for the structure and IR spectra of ethylene glycol-9 water molecules and ethylene glycol-9 water molecules-M⁺ systems, where M⁺ = Na⁺, K⁺. The presence of cations changes the structure of the glycol hydrate shell, which leads to a decrease in the activation energy of glycol self-diffusion in the solution with the addition of salts in comparison with its value in the water-glycol solution.     

Excess and partial excess molar volumes of mixing trimethyl- and triethylphosphate with water

Excess and excess partial molar volumes of mixing of the systems trimethylphosphate (TMP) and triethylphosphate (TEP) with water were determined at 15, 20, 25, 30 and 35°C. Negative deviation from ideal behavior were observed for the two systems studied, with a minimum at x _TMP =0.40 and x _TEP =0.35. Excess volume values in general decrease with temperature, and are smaller for the TMP-water system.     

Excess molar volumes and molar refraction of 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone+water water from 5 to 45°C

The excess molar volumes and molar refractionsR ₁₂ of 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU)+water have been determined over the entire mole fraction range at 10° intervals from 5 to 45°C and at atmosphere pressure. The excess volumes are all negative and they become more positive with increase of temperature. Limiting partial molar volumes for DMPU in water and water in DMPU are also reported.     

Molar excess heat capacities and volumes for mixtures of benzonitrile with cyclohexane between 10 and 45°C

The heat capacities and volumes for binary mixtures of benzonitrile with cyclohexane were determined at 10, 25, and 45°C. The dependence of the molar excess heat capacities on temperature and composition are interpreted in terms of the thermal relaxation of associated benzonitrile molecules into monomeric species.To whom correspondence should be addressed.     

Excess and partial excess molar volumes of mixing of N,N-dibutyl-2-ethylhexamide with dodecanol

Excess and excess partial molar volumes of mixing of the system N,N-dibutyl-2-ethylhexylamide (DBEHA) + dodecanol (DDA) were determined at 25, 35, 45, 55 and 65°C. The excess molar volumes exhibit a maxima at each temperature at approximatelyx _DBEHA = 0.3 and a minima close tox _DBEHA = 0.9. The values of the excess volumes in general increase with the temperature. The partial excess molar volumes are calculated from the smoothed data and the results are discussed in the light of postulated amide-alcohol interactions.     

Excess molar enthalpies of binary mixtures containing poly(ethylene glycol) 200+four cyclic ethers at (288.15, 298.15 and 313.15) K and at atmospheric pressure

Excess molar enthalpies, H_m^E, of binary mixtures containing poly(ethylene glycol) (PEG) 200+1,3-dioxolane, PEG 200+1,4-dioxane, PEG 200+oxolane and PEG 200+oxane were determined using a flow microcalorimeter at (288.15, 298.15 and 313.15) K and at atmospheric pressure. The H_m^E curves are always positive, with maxima varying from 393 J mol⁻¹ (1,3-dioxolane) to 658 J mol⁻¹ (oxolane), showing asymmetrical trends. The effect of the temperature is well marked on the calorimetric data that increase as the temperature is increased. The Redlich-Kister polynomial was used to estimate the binary fitting parameters. Root-mean-square deviations from the regression lines are reported.     

Structure and property of the hydrogen bonding complex between triazines and water

The study of the intermolecular interactions that drive the solvation of six-membered nitrogenated aromatic rings is of particular importance since they are known to constitute key building blocks of pro- teins and nucleotides[1―5]. The investigation of the 1:1 adduct of these molecules with water will be the first step in the understanding of such interactions. These molecules possess two different proton-acceptor sites: the ring π cloud and the lone pairs of electrons on the nitrogen atoms…     

Viscosity of binary mixtures of 2-ethoxyethanol with ethylene glycol,diethylene glycol,triethylene glycol and tetraethylene glycol systems at T = (293.15, 298.15 and 303.15) K

Viscosities, at T = 293.15, 298.15 and 303.15 K, in the binary mixtures of 2-ethoxyethanol with ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol have been measured as a function of composition. From the experimental data the deviations in the viscosity have been calculated. The viscosity data, at T = 298.15 K, were correlated with equations of Hind et al., Grunberg and Nissan, and Frenkel. The results are discussed in terms of intermolecular interactions and structural properties of studied binary mixtures.     

Excess molar enthalpies of binary mixtures containing ethylene glycols or poly(ethylene glycols) + ethyl alcohol at 308.15 K and atmospheric pressure

Excess molar enthalpies, , of binary mixtures containing ethylene glycols and poly(glycols) + ethyl alcohol were measured by a flow microcalorimeter at 308.15 K and at atmospheric pressure over the whole composition range. Binary mixtures contain ethyl alcohol + ethylene glycol, + di(ethylene glycol), + tri(ethylene glycol), + tetra(ethylene glycol), + poly(ethylene glycol)-200, + poly(ethylene glycol)-300, + poly(ethylene glycol)-400, + poly(ethylene glycol)-600. Effects of the molecular weight distribution (MWD), of the polymer were investigated too, by preparing three additional samples of poly(ethylene glycol) with the same number average molecular weight (M_n ≈ 300), but different MWD. For all mixtures, results were fitted to the Redlich–Kister polynomial. curves are asymmetrical, showing positive values which vary from 280 J mol⁻¹ (diethylene glycol + ethyl alcohol) to 1034 J mol⁻¹ (mixture containing PEGs (200 + 400) + ethyl alcohol). Effects of changes in the glycols chain length and in MWD on the molecular interactions among the mixture components are discussed.     

A computational study of interactions between acetic acid and water molecules

Density functional theory calculations were performed for the title reactions to elucidate the difference between the strong cyclic hydrogen bond of (Me-COOH)(2) and the electrolytic dissociation, MeCOOH <==> Me-COO(-) + H(+), as a weak acid. The association of water clusters with acetic acid dimers strengthens the cyclic hydrogen bond. A nucleophilic attack of the carboxylic carbon by a water cluster leads to a first zwitterionic intermediate, MeCOO(-) + H(3)O(+) + (HO)(3)C-Me. The intermediate is unstable and is isomerized to a neutral interacting system, MeCOOH...(HO)(3)C-Me + H(2)O. The ethanetriol, (HO)(3)-CMe is transformed to an acetic acid monomer. The monomer may be dissociated to give a second zwitterionic intermediate with reasonable proton-relay patterns and energy changes. In proton relay reaction channels, H in MeCOOH is not an acidic proton but is always a hydroxy proton.     

Apparent molal volumes and adiabatic compressibilities of ethylene glycol derivatives in water at 5, 25, and 45°C

Density and ultrasonic velocity measurements were made on a series of dilute equeous solutions of H(OCH ₂ CH ₂ )_nOH, CH ₃ (OCH ₂ CH ₂ )_nOCH ₃ , H(CH ₂ )_nOCH ₂ CH ₂ OH (n=1–4), and poly(ethylene glycol) at 5, 25, and 45°C. The additivity of the limiting partial molal volumes ( ) and adiabatic compressibilities ( ) for CH ₂ and CH ₂ CH ₂ O groups was tested by using the observed and values of the solutes. The and values of the CH ₃ , CH ₂ , CH ₂ CH ₂ O, and CH ₂ OH groups were estimated and discussed in relation to hydration effects. The and values of alkoxyethanols calculated on the basis of the additivity of the group partial molal quantities were in good agreement with the observed values. The behavior of the limiting partial molal isothermal compressibility of alkoxyethanols was similar to that of the adiabatic compressibility.     

Sodium Hydrogen Sulfate in Poly(ethylene glycol). An Efficient Recyclable System for the Deprotection of 1,1-Diacetates

Summary. Poly(ethylene glycol) was used as the solvent for selective deprotection of 1,1-diacetates (acylals) with easy recyclability of solvent and sodium hydrogen sulfate catalyst. This method is high yielding, fast, clean, safe, and therefore very suitable for practical organic synthesis.     

Apparent molar volume, isentropic compressibility and conductivity of di-sodium hydrogen phosphate in water and in aqueous solutions of 1-propanol

Precise measurements on the density and sound velocity of solutions of di-sodium hydrogen phosphate in 1-propanol + water mixed-solvent media with alcohol mass fractions of 0.00, 0.05, 0.10 and 0.15 are reported in the 283.15–303.15 K temperature range at 5 K intervals. Electrical conductivity and refractive index of the solutions are studied at 298.15 K. From the experimental density and sound velocity data, the apparent molar volume and isentropic compressibility values of di-sodium hydrogen phosphate have been evaluated. The results show a positive transfer volume of di-sodium hydrogen phosphate from an aqueous 1-propanol solution to a more concentrated 1-propanol solution. The apparent molar isentropic compression of di-sodium hydrogen phosphate in aqueous 1-propanol solutions is negative and it increases with increasing the concentration of 1-propanol and temperature. The negative values of apparent molar isentropic compression imply that the water molecules around the di-sodium hydrogen phosphate are less compressible than the water molecules in the bulk solutions. The effects of the electrolyte concentration and relative permittivity of the medium on the molar conductivity were also investigated.     

Volumetric and optical study of molecular association in binary mixtures of dimethyl sulphoxide with carboxylic acid

Density and refractive index have been measured for the binary mixture of dimethyl sulphoxide (DMSO) with propanoic acid and n-butyric acid at three temperatures, 293, 303 and 313 K, over the entire composition range. Excess parameters such as excess molar volume (V ^E) and molar refraction deviation (ΔR _m) have been calculated from the measured density and refractive index to study the molecular association between the component molecules. The V ^E and ΔR _m values of these mixtures were fitted to the Redlich–Kister polynomial equation. Both excess parameters were plotted against the mole fraction of DMSO over the whole composition range. The values of V ^E and ΔR _m have been found to be negative for both mixtures over the entire composition range, which suggests the presence of strong intermolecular interaction. The experimental refractive data of these mixtures were also used to test the validity of the empirical relations for the refractive index.     

Thermodynamic properties of the ethylammonium nitrate + water system: Partial molar volumes,heat capacities,and expansivities

Partial molar volumes at 15, 25, and 45°C and partial molar heat capacities and expansivities at 25°C for ethylammonium nitrate + water mixtures are reported. The results are compared with those for other aqueous cosolvents, particularly hydrazine and ammonium nitrate.