Liquid-liquid equilibria of (water + butyric acid + diethyl succinate or diethyl glutarate or diethyl adipate) ternary systems

Liquid-liquid equilibrium (LLE) data of the solubility (binodal) curves and tie-line end compositions were examined for mixtures of {(water (1) + butyric acid (2) + diethyl succinate or diethyl glutarate or diethyl adipate (3)} at 298.2 K and 101.3 ± 0.7 kPa. The relative mutual solubility of butyric acid is higher in the diethyl succinate or diethyl glutarate or diethyl adipate layers than water layers. The consistency of the experimental tie-lines was determined through the Othmer-Tobias correlation equation. The LLE data were correlated with NRTL model, indicating the reliability of the NRTL equations for these ternary systems. The best results were achieved with the NRTL equation, using non-randomness parameter (α = 0.3) for the correlation. Distribution coefficients and separation factors were measured to evaluate the extracting capability of the solvents.     

Surface tension of pentafluoroethane + 1,1-difluoroethane from (243 to 328) K

The surface tension of the binary refrigerant mixture pentafluoroethane (HFC-125) + 1,1-difluoroethane (HFC-152a) was measured in the temperature range from (243 to 328) K with a differential capillary rise method, for three compositions around the composition of the optimum refrigeration performance (HFC-125 + HFC152a, 15%/85%). The uncertainties of the measurement of the temperature and the surface tension were estimated to be within ±10 mK and ±0.2 mN m⁻¹, respectively. A correlation for the surface tension of the binary refrigerant mixture HFC-152a + HFC-125 was developed as a function of the composition.     

Surface tension of dimethyl ether + propane from 243 to 333 K

The surface tension of the binary refrigerant mixture dimethyl ether (RE170)(1) + propane (R290)(2) at three mass fraction of w₁=0.3007,0.4975 ??and ??0.6949$w_1=\mathrm{0.3007,0.4975}\text{\hspace{0.17em}??}\text{and}\text{\hspace{0.17em}??}0.6949$ was measured in the temperature range from 243 to 333 K with a differential capillary rise method. The uncertainties of the measurement of the temperature and the surface tension were estimated to be within ±10 mK and ±0.2 mN m⁻¹, respectively. A correlation for the surface tension of the binary refrigerant mixture RE170 + R290 was developed as a function of the composition.     

Surface tension of 1-alkyl-3-methylimidazolium based ionic liquids with trifluoromethanesulfonate and tetrafluoroborate anion

The amount of available accurate experimental data on the surface tension of ionic liquids is still limited; in many cases the data are rare or even absent. In the present study, air-liquid interfacial tension data were determined experimentally for five 1-C_n-3-methylimidazolium based ionic liquids (n = 2, 4, and 6), three with trifluoromethanesulfonate and two with tetrafluoroborate anion, at atmospheric pressure in the temperature range from 268 to 356 K. The resultant surface tension data are average values of the measurements repeated many times at each set point temperature. The accuracy of the results, was confirmed by employing the Wilhelmy plate and the du Noüy ring methods in parallel, using the Krüss K100MK2 tensiometer. For the Wilhelmy plate data the combined standard uncertainty is estimated to be about 0.05 mN m⁻¹. The data obtained by du Noüy method show about up to seven times greater scatter than those obtained by the Wilhelmy plate method. To the 50 up to now published surface tension values for the five studied ionic liquids the present study adds further 175 data points. In contrast to that of n-alkanes, the surface tension of 1-alkyl-3-methylimidazolium based ionic liquids decreases and their surface entropy increases with the cation alkyl chain length.     

Phase equilibria on binary systems containing diethyl sulfide

Isothermal vapor-liquid equilibrium (VLE) of the following systems was measured with a recirculation still: diethyl sulfide + ethanol at 343.15 K, diethyl sulfide + 1-propanol at 358.15 K, and diethyl sulfide + propyl acetate at 363.15 K. Diethyl sulfide + ethanol at 343.15 K and diethyl sulfide + 1-propanol at 358.15 K systems exhibit positive deviation from Raoult's law, whereas diethyl sulfide + propyl acetate at 363.15 K system exhibits only slight positive deviation from Raoult's law. A maximum pressure azeotrope was found in the systems diethyl sulfide + ethanol (x₁ = 0.372, P = 88.4 kPa, T = 343.15 K) and diethyl sulfide + 1-propanol (x₁ = 0.640, P = 96.8 kPa, T = 358.15 K). No azeotropic behavior was found in diethyl sulfide + propyl acetate system at 363.15 K. The experimental results were correlated with the Wilson model and compared to COSMO-SAC predictive model. Liquid and vapor phase compositions were determined with gas chromatography. All measured data sets passed the thermodynamic consistency tests. The activity coefficients at infinite dilution are also presented.     

Characterization of recognition sites for diethyl 4-nitrobenzylphosphonate, an organophosphate pesticide analogue

In a first step towards chemical sensors using molecular imprinted materials, the complexing characteristics of diethyl 4-nitrobenzylphosphonate, an organophosphate pesticide analogue, have been studied. Two molecules have been assessed as potential interacting moieties, specifically a fluoroalcohol and an aromatic acid. The interactions have been first characterized by regular methods, such as ¹H, ³¹P NMR and IR spectroscopy. These showed a stoichiometry 1/1 for both complexes and association constants, respectively, close to 40 ± 10 and 12 ± 2 M⁻¹. In a second step, isothermal titration calorimetry was used and a method was developed to obtain low-association constants. The association constant could be obtained for the fluoroalcohol ligand and was found equal to 63 ± 0.7 M⁻¹. For the acidic molecule, an appropriate model could not be found, preventing the evaluation of this constant.     

Thermodynamic properties of hydrated sodium l-threonate Na(C4H7O5)·H2O(s)

Low-temperature heat capacities of the compound Na(C₄H₇O₅)·H₂O(s) have been measured with an automated adiabatic calorimeter. A solid-solid phase transition and dehydration occur at 290-318 K and 367-373 K, respectively. The enthalpy and entropy of the solid-solid transition are Δ_transH_m = (5.75 ± 0.01) kJ mol⁻¹ and Δ_transS_m = (18.47 ± 0.02) J K⁻¹ mol⁻¹. The enthalpy and entropy of the dehydration are Δ_dH_m = (15.35 ± 0.03) kJ mol⁻¹ and Δ_dS_m = (41.35 ± 0.08) J K⁻¹ mol⁻¹. Experimental values of heat capacities for the solids (I and II) and the solid-liquid mixture (III) have been fitted to polynomial equations.     

Low-temperature heat capacity and thermodynamic properties of crystalline carboxin (C12H13NO2S)

Carboxin was synthesized and its heat capacities were measured with an automated adiabatic calorimeter over the temperature range from 79 to 380 K. The melting point, molar enthalpy (Δ_fusH_m) and entropy (Δ_fusS_m) of fusion of this compound were determined to be 365.29±0.06 K, 28.193±0.09 kJ mol⁻¹ and 77.180±0.02 J mol⁻¹ K⁻¹, respectively. The purity of the compound was determined to be 99.55 mol% by using the fractional melting technique. The thermodynamic functions relative to the reference temperature (298.15 K) were calculated based on the heat capacity measurements in the temperature range between 80 and 360 K. The thermal stability of the compound was further investigated by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. The DSC curve indicates that the sample starts to decompose at ca. 290 °C with the peak temperature at 292.7 °C. The TG-DTG results demonstrate the maximum mass loss rate occurs at 293 °C corresponding to the maximum decomposition rate.     

Compressed liquid densities of 1,1,1,3,3-pentafluoropropane (HFC-245fa) and 1,1,1,3,3,3-hexafluoropropane (HFC-236fa)

Densities of 1,1,1,3,3-pentafluoropropane (HFC-245fa) and 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) have been measured for temperatures from 293 to 373 K and pressures up to 70 MPa, with a high-pressure vibrating tube densimeter system in the liquid state. The system was calibrated using water and vacuum via the method of Lagourette et al. The uncertainty in the density measurement was estimated to be ±0.6 kg m⁻³. The experimental results were correlated to a Tait equation. The average absolute percentage deviations of measurement results from the correlations of HFC-245fa and HFC-236fa are 0.0096% and 0.031%, respectively.     

Heat capacity and thermodynamic properties of crystalline ornidazole (C7H10ClN3O3)

The molar heat capacities of 1-(2-hydroxy-3-chloropropyl)-2-methyl-5-nitroimidazole (Ornidazole) (C₇H₁₀ClN₃O₃) with purity of 99.72 mol% were measured with an adiabatic calorimeter in the temperature range between 79 and 380 K. The melting-point temperature, molar enthalpy, Δ_fusH_m, and entropy, Δ_fusS_m, of fusion of this compound were determined to be 358.59±0.04 K, 21.38±0.02 kJ mol⁻¹ and 59.61±0.05 J K⁻¹ mol⁻¹, respectively, from fractional melting experiments. The thermodynamic function data relative to the reference temperature (298.15 K) were calculated based on the heat capacities measurements in the temperature range from 80 to 380 K. The thermal stability of the compound was further investigated by DSC and TG. From the DSC curve an intensive exothermic peak assigned to the thermal decomposition of the compound was observed in the range of 445-590 K with the peak temperature of 505 K. Subsequently, a slow exothermic effect appears when the temperature is higher than 590 K, which is probably due to the further decomposition of the compound. The TG curve indicates the mass loss of the sample starts at about 440 K, which corresponds to the decomposition of the sample.     

Surface energies of linear and cross-linked polymers based on isobornyl methacrylate and methacryl-heptaisobutyl POSS

The use of monofunctional polyhedral oligomeric silsesquioxanes (POSS) as polymer modifiers requires controlling the phase separation process producing POSS-rich and polymer-rich domains that occurs in most systems due to the thermodynamic incompatibility between both components. One significant result of this study is the finding that isobornyl methacrylate (IBoMA) is an excellent reactive solvent of a commercial methacryl-heptaisobutyl POSS (MA-POSS). Formulations containing up to 30 wt% MA-POSS in IBoMA or in IBoMA (95 parts by weight)-diethylene glycol dimethacrylate (DEGDMA, 5 parts by weight), were polymerized using benzoyl peroxide as initiator up to complete conversion of CC bonds (determined by FTIR). Transparent POSS-modified materials were obtained without any evidence of a macroscopic phase separation. POSS addition produced a decrease of the glass transition temperature and the glassy and rubbery elastic modulus. A significant decrease in surface energy for both linear and cross-linked polymers was observed. This effect was particularly important for cross-linked polymers where the addition of 30 wt% POSS decreased the surface energy from about 29 mN m⁻¹ to 16 mN m⁻¹, a very low value for hydrocarbon materials. This study opens a way to obtain hydrophobic methacrylic coatings without the use of fluorinated monomers.     

Thermophysical properties for (diethyl carbonate + p-xylene + octane) ternary system

The density and speed of sound of the ternary mixture (diethyl carbonate + p-xylene + octane) have been measured at atmospheric pressure and in the temperature range T = (288.15 to 308.15) K. Besides, surface tension has been also determined for the same mixture at T = 298.15 K. The experimental measurements have allowed the calculation of the corresponding derived properties: excess molar volumes, excess isentropic compressibilities, and surface tension deviations. Excess properties have been correlated using Nagata and Tamura equation and correlation for the surface tension deviation has been done with the Cibulka equation. Good accuracy has been obtained. Based on the variations of the derived properties values with composition, a qualitative discussion about the intermolecular interactions was drawn.     

Synthesis of novel soluble poly(imide-siloxane)s via hydrosilylation: Characterization and structure property behaviour

A series of novel poly(imide-siloxane)s (PIS) were synthesized by the grafting of amine terminated soluble imides to the siloxane backbone. The amine terminated imides were synthesized by choosing suitable anhydrides and amines to get the imides that are soluble in polar and non-polar solvents. The imides were grafted to the siloxane backbone by the epoxy group cleavage. All the polymers were obtained in quantitative yields with the inherent viscosities ranging from 0.22 to 1.2 dL g⁻¹. The polymers were characterized by FT-IR, ¹H and ¹³C NMR, and were examined for their thermal properties. The polymers were found to be stable up to a temperature 350 °C. The DSC results showed a single glass transition in the negative temperature, whereas the DTA revealed another glass transition in the positive end for some of the polymers showing phase separation. Polymer films were prepared employing the coupling reaction between PIS and the polydimethylsiloxane matrix by varying the amount of incorporation of PIS in the films. The polymer films had a tensile strength of 35-82 MPa with a percentage elongation of 86-271%. The contribution of polar and dispersion component towards the total surface energy was studied by the contact angle measurement and a reduction in surface tension of 14 mN m⁻¹ was achieved with the fluorine containing PIS membrane.     

Solid-liquid interfacial energy for solid succinonitrile in equilibrium with succinonitrile dichlorobenzene eutectic liquid

The equilibrated grain boundary groove shapes for solid succinonitrile (SCN) in equilibrium with the succinonitrile (SCN) dichlorobenzene (DCB) eutectic liquid were directly observed. From the observed grain boundary groove shapes, the Gibbs-Thomson coefficient and solid-liquid interfacial energy for solid SCN in equilibrium with the SCN DCB eutectic liquid have been determined to be (5.43 ± 0.27) × 10⁻⁸ K m and (7.95 ± 0.80) × 10⁻³ J m⁻² with present numerical method and Gibbs-Thomson equation, respectively. The grain boundary energy of SCN rich phase of the SCN DCB eutectic system has been determined to be (14.77 ± 1.77) × 10⁻³ J m⁻² from the observed grain boundary groove shapes. Thermal conductivity of eutectic solid phase and eutectic liquid phase at the eutectic melting temperature have also been measured to be 0.269 and 0.231 W/K m, respectively.     

Heat-capacity measurements and thermodynamic functions of crystalline adenine; revised thermodynamic properties of aqueous adenine

The standard molar heat capacity C^°_p,m of adenine(cr) has been measured using adiabatic calorimetry over the range 6<(T/K)<310 and the results used to derive thermodynamic functions for adenine(cr) at smoothed temperatures. At T=298.15 K, C^°_p,m=(142.67±0.29) J · K⁻¹ · mol⁻¹ and the third law entropy S^°_m=(145.62±0.29) J · K⁻¹ · mol⁻¹. The standard molar Gibbs free energy of formation Δ_fG^°_m at T=298.15 K for crystalline adenine was calculated, using the standard molar enthalpy of formation for the compound and entropies of the elements from the literature, and found to be Δ_fG^°_m=(301.4±1.0) kJ · mol⁻¹. The results were combined with solution calorimetry and solubility measurements from the literature to yield revised values for the standard molar thermodynamic properties of aqueous adenine at T=298.15 K: Δ_fG^°_m=(313.4±1.0) kJ · mol⁻¹, Δ_fH^°_m=(129.5±1.4) kJ · mol⁻¹, and S_m^°=(217.68±0.44) J · K⁻¹ · mol⁻¹.     

Low-temperature heat-capacity and standard molar enthalpy of formation of copper l-threonate hydrate Cu(C4H6O5)·0.5H2O(s)

The solid copper l-threonate hydrate, Cu(C₄H₆O₅)·0.5H₂O, was synthesized by the reaction of l-threonic acid with copper dihydrocarbonate and characterized by means of chemical and elemental analyses, IR and TG-DTG. Low-temperature heat-capacity of the title compound has been precisely measured with a small sample precise automated adiabatic calorimeter over the temperature range from 77 to 390 K. An obvious process of the dehydration occurred in the temperature range between 353 and 370 K. The peak temperature of the dehydration of the compound has been observed to be 369.304 ± 0.208 K by means of the heat-capacity measurements. The molar enthalpy, Δ_dH_m, of the dehydration of the resulting compound was of 16.490 ± 0.063 kJ mol⁻¹. The experimental molar heat capacities of the solid from 77 to 353 K and the solid from 370 to 390 K have been, respectively, fitted to tow polynomial equations with the reduced temperatures by least square method. The constant-volume energy of combustion of the compound, Δ_cU_m, has been determined as being −1616.15 ± 0.72 kJ mol⁻¹ by an RBC-II precision rotating-bomb combustion calorimeter at 298.15 K. The standard molar enthalpy of formation of the compound, , has been calculated to be −1114.76 ± 0.81 kJ mol⁻¹ from the combination of the data of standard molar enthalpy of combustion of the compound with other auxiliary thermodynamic quantities.     

Electrosyntheses of high quality poly(5-methylindole) films in mixed electrolytes of boron trifluoride diethyl etherate and diethyl ether

High quality poly(5-methylindole) (P5MeI) films, especially with good fluorescence properties, were synthesized electrochemically by direct anodic oxidation of 5-methylindole in boron trifluoride diethyl etherate (BFEE) containing additional 50% diethyl ether (EE) (by volume). The oxidation potential onset of 5-methylindole in this medium was measured to be only 0.84 V vs. SCE, which was much lower than that determined in acetonitrile + 0.1 mol L⁻¹ TBATFB (1.08 V vs. SCE). P5MeI films obtained from this medium showed good electrochemical behavior and good thermal stability with conductivity of 10⁻² S cm⁻¹, indicating that BFEE was a better medium than acetonitrile for the electrosyntheses of P5MeI films. Dedoped P5MeI films were thoroughly soluble in strong polar solvent such as dimethyl sulfoxide (DMSO). ¹H NMR spectroscopy and FT infrared spectrum of dedoped P5MeI films strongly suggested that the monomers were linked via the positions 2 and 3. Fluorescent spectral studies indicated that P5MeI was a good violet-blue light emitter with the excitation and emission wavelength of 310 nm and 418 nm, respectively. To the best of our knowledge, this is the first case that 5-methyl group substituted polyindole films with good fluorescence properties can be electrodeposited.     

Thermodynamic properties of the gaseous barium silicates BaSiO2 and BaSiO3

In the present study, the stability of gaseous barium silicates was confirmed by the high temperature mass spectrometry. On the basis of equilibrium constants measured for gas-phase reactions, the standard formation enthalpies were determined for gaseous barium silicates as (−510 ± 15) kJ · mol⁻¹ and (−884 ± 18) kJ · mol⁻¹ at 298 K; standard atomization enthalpies as (1637 ± 17) kJ · mol⁻¹ and (2318 ± 20) kJ · mol⁻¹ at 298 K for BaSiO₂ and BaSiO₃, respectively. Based on the results obtained the critical analysis of the literature data was carried out.     

Conformations and vibrational properties of disulfide bridges: Potential energy distribution in the model system diethyl disulfide

Disulfide bridges are important structural elements in proteins. It is well-known that the position of the characteristic disulfide band at ca. 500 cm⁻¹ in the vibrational spectra varies with the conformation around the disulfide unit. In our computational study on the model system diethyl disulfide, both wavenumber and normal mode composition are analyzed simultaneously as a function of conformation. For the disulfide band, a negative correlation between the calculated vibrational wavenumber and the SS stretching contribution is detected. This trend in the normal mode composition provides an explanation for experimentally observed wavenumber shifts of the disulfide band.     

Binary diffusion coefficients of phenolic compounds in subcritical water using a chromatographic peak broadening technique

Infinite dilution diffusion coefficients of certain phenolic compounds were measured as a function of temperature in water slightly acidified with formic acid using the Taylor dispersion method. The diffusion coefficients calculated using the chromatographic peak broadening technique were found to increase exponentially with an increase in the temperature. The diffusion coefficients of the selected phenolic compounds did not vary as a function of their molecular weights and the diffusion coefficients of the phenolic compounds increased as a function of temperature (from 2.16 × 10⁻¹⁰ m² s⁻¹ at 298 K to 5.79 × 10⁻¹⁰ m² s⁻¹ at 413 K for malvidin-3,5-diglucoside). However, for some phenolic compounds such as gallic acid monohydrate, quercetin-3-β-d-glucoside, protocatechuic acid and (−)-epicatechin, there were difficulties in making measurements above temperatures of 352 K, 372 K, 392 K and 413 K, respectively, due to thermal degradation of the phenolic compounds in water above these temperatures. The experimentally measured diffusion coefficients of the phenolic compounds were correlated as a function of temperature and solvent viscosity and were compared with those predicted using theoretical models. The validity of the Stokes-Einstein diffusion model in predicting the diffusion coefficients of the phenolic compounds in hot pressurized water was also evaluated.