Calorimetric study of the solvation of benzene and its chloro-, nitro-, and aminoderivatives by n-hexane, 1-butanol, and mixed solvent n-hexane-1-butanol

The heats of dissolution of benzene, chlorobenzene, ortho-dichlorobenzene, nitrobenzene, and aniline in n-hexane and 1-butanol and those of benzene, chlorobenzene, nitrobenzene, and aniline in a mixture of n-hexane and 1-butanol were measured by calorimetry at 25°C. The enthalpies of solvation of the compounds were calculated. The correlation between the enthalpies of solvation of the compounds and their molar refraction was studied. The enthalpies of solvation of the compounds and their functional groups by the mixture of n-hexane and 1-butanol were considered.     

Enthalpies of solution of <Emphasis Type="Italic">n</Emphasis>-alkanes in mixtures of MeCN with alkan-1-ols at 298.15 K. Relations between the thermodynamic properties of binary and ternary systems

The solution enthalpies of n-hexane, n-nonane, and n-undecane in mixtures of MeCN with EtOH, PrOH, and BuOH were determined by calorimetric method at 298.15 K. Relations between the thermodynamic properties of ternary systems and the properties of the binary solvents and the solute are discussed. To predict the enthalpies of solution of hydrocarbons in mixed solvents whose components have strongly different molar volumes (V ₂/V ₁ > 1.5), it is proposed to use the values that are additive in the volume fraction scale. The solution enthalpies of hydrocarbons in mixtures characterized by close molar volumes of the components strongly depend on the excess properties of the binary solvent.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1578–1582, August, 2004.     

Activity coefficients of hydrocarbon solutes at infinite dilution in the ionic liquid, 1-methyl-3-octyl-imidazolium chloride from gas–liquid chromatography

Activity coefficients for hydrocarbon solutes at infinite dilution in 1-methyl-3-octyl-imidazolium chloride have been measured using the medium pressure gas–liquid chromatography method. The hydrocarbon solutes used were n-pentane, n-hexane, n-heptane, n-octane, 1-hexene, 1-heptene, 1-octene, 1-hexyne, 1-heptyne, 1-octyne, cyclopentane, cyclohexane, cycloheptane, benzene, and toluene. Activity coefficients at infinite dilution were determined at the following three temperatures (298.15, 308.15, and 318.15) K. Selectivities for benzene and the hydrocarbons are presented and the results indicate that 1-methyl-3-octyl-imidazolium chloride is a reasonable solvent for the separation of an alkane or an alkene from benzene.     

Preferential sorption and permeation of binary liquid mixtures in poly (vinyl chloride) membrane by pervaporation

Preferential sorptions and pervaporation selectivities in poly (vinyl chloride) (PVC) membrane for various binary liquid mixtures were investigated. Methanol/n-propanol, benzene/n-hexane, and ethanol/water mixtures were selected as the binary liquid mixture. In the methanol/n-propanol mixture, methanol was preferentially sorbed in the PVC membrane and predominantly permeated. In the benzene/n-hexane mixture, benzene was incorporated and permeated preferentially. In the ethanol/water mixture, ethanol was preferentially sorbed in the PVC membrane and water was preferentially permeated. The preferential sorptions were analyzed according to Mulder's model derived from Flory-Huggins thermodynamics. The pervaporation selectivity in these systems were discussed using a sorption selectivity and diffusion selectivity. © 1995 John Wiley & Sons, Inc.     

Enthalpy of hydrogen bonded alcohol-butyl amine complexes by a simpler calorimetric method

The heats of mixing ofn-butyl amine with methanol andn-propanol have been determined at 30° C and the enthalpies of alcohol-amine complex formation have been calculated by thermochemical cycle. The enthalpies of complex formation of butyl amine with methanol andn-propanol were found to be-44.3 kJ/mole and-39.4 kj/mole respectively. The heats of mixing of synthetically prepared 1:1 molar mixtures of n-butyl amine with methanol, ethanol andn-propanol withn-hexane have also been determined at 30° C. The enthalpy of amine-alcohol complexes was obtained from the partial molar heats of dissociation of the complexes inn-hexane. The values agree with those obtained by the thermochemical cycle method. NCL Communication No. 2561.     

Liquid Solution Densities of Ternary-Pseudobinary Mixtures of (Benzene + Cyclohexane) in the Presence of Tetrachloromethane or <Emphasis Type="Italic">n</Emphasis>-Hexane

Densities have been obtained as a function of composition for ternary-pseudobinary mixtures of [(benzene + tetrachloromethane or n-hexane) + (cyclohexane + tetrachloromethane or n-hexane)] at atmospheric pressure and the temperature 298.15 K, by means of a vibrating-tube densimeter. Excess molar volumes, V_m^E, partial molar volumes and excess partial molar volumes were calculated from the density data. The values of V_m^E have been correlated using the Redlich–Kister equation and the coefficients and standard errors were estimated. The experimental and calculated quantities are used to discuss the mixing behavior of the components. The results show that the third component, CCl₄ or n-C₆H₁₄, have quite different influences on the volumetric properties of binary liquid mixtures of benzene with cyclohexane.     

Evaluation of the Thermodynamic Parameters for the Adsorption of Some Hydrocarbons on Chemically Treated-Bentonites by Inverse Gas Chromatography

Inverse gas chromatography has been used to evaluate the adsorption parameters (ΔH_a, ΔH_st, ΔS_a and ΔG_a) of some probe molecules, each representing a class of organic (n-hexane, cyclohexane, benzene, n-octane, 1-octene and isooctane) on bentonite and chemically treated-bentonites. The adsorption parameters of the probes on the bentonite samples were determined in infinite dilution region. Adsorption of the organic species was investigated in the temperature range of 200–275^∘C, using a flame ionization detector, and nitrogen as a carrier gas. The net retention volumes (V_n) of the probes were determined by the help of the retention times (t_R) observed on gas chromatograms for each probe. Injection was made at least three times for each probe, obtaining reproducible results of ± 0.5%. It was found that benzene exhibits more negative ΔH than for n-hexane and cyclohexane on all of the adsorbents. In addition, it was found that 1-octene exhibits more negative ΔH than for n-octane and isooctane on the chemically treated-bentonites, whereas n-octane exhibits more negative ΔH than for 1-octene and isooctane on the natural bentonite. Also, interactions of benzene with the natural- and chemically treated-bentonites were found to be stronger than those of n-hexane and cyclohexane with the same carbon number. Again, interactions of the 1-octene with the chemically treated-bentonites were found to be stronger those of n-octane and isooctane with the same carbon number. On the contrary, interactions of n-octane with the untreated-bentonite were found to be stronger than those of 1-octene and isooctane.     

Enthalphy of mixing of bromobenzene with n-alkanes,with cyclohexane,and with benzene

A dynamic flow microcalorimeter of the Picker design was used to measure enthalpies of mixing at 298.15 K and atmospheric pressure of the six binary systems bromobenzene + n-hexane, + n-heptane, + n-nonane, + n-tetradecane, + cyclohexane, and + benzene. Within the homologous series of n-alkane systems, the interaction parameter, h₁₂, calculated from rigid-lattice group contribution theory, decreases weakly with increasing chain length of the alkane. This behavior is quite analogous to that observed with chloro-derivatives of benzene + n-alkane.     

Thermodynamics of organic mixtures containing amines - III: Molar Excess Volumes at 298.15 K for Tripropylamine +n‐Alkane Systems ‐ Application of the Flory Theory to N,N,N‐Trialkylamine + n‐Alkane Mixtures

Molar excess volumes at 298.15 K and atomospheric pressure for tripropylamine + n-hexane, + n-octane, + n-decane, + n-dodecane or + n hexadecane systems determined from densities measured with an Anton-Paar DMA 602 vibrating-tube densimeter are reported. N,N,N-trialkylamine + n-alkane systems have been studied using the Flory theory. Better results on excess enthalpies are obtained when the difference in size between the mixture components is large.

The dependence of the excess volume at equimolar composition with the length of the n-alkane is correctly described. The simultaneous analysis of the experimental excess volumes and of the excess enthalpies reveal that free volume effects are important in systems formed by triethylamine or tripropylamine and longer alkanes, as well as in those involving tripropylamine or tributylamine and the shorter alkanes.

The Patterson effect is present in the studied mixtures. The more globular amines, triethylamine, tripropylamine or tributylamine are order breakers of the longer alkanes. The amines of very large size, e.g., tridodecylamine, show an ordered structure.     

Pyrene fluorescence measurements of metastable oil droplets in surfactant-free oil-in-water emulsions

 The fluorescence behavior of pyrene in oil droplets of a surfactant-free oil-in-water emulsion was studied for benzene, fluorobenzene, n-hexane and cyclohexane droplets in water. The excimer–monomer fluorescence ratio immediately after sonication, I _E/I _M(0), of the benzene/water emulsion was 8–10 times larger than for the benzene solution. The ratio I _E/I _M(t) increased in the first 10–20 min before it decreased to zero. Similar behavior was observed for the fluorobenzene/water emulsion, while I _E/I _M(0) for emulsions with n-hexane and cyclohexane was smaller than for benzene and fluorobenzene/water emulsions. I _E/I _M(t) hardly changed with time for the n-hexane and cyclohexane/water emulsions. This different behavior was attributed to the increased solubility of nanometer-size droplets with benzene and fluorobenzene. Received: 20 June 2001 Accepted: 19 April 2001     

Application of the principle of congruence to ternary alkane mixtures

Excess enthalpies and excess volumes at 298.15 K and atmospheric pressure have been measured for mixtures of n-hexane + (an equimolar mixture of n-tridecane + n-nonadecane). The agreement of the results with the corresponding results for mixtures of n-hexane + n-hexadecane is interpreted as confirmation of the applicability of the principle of congruence to multicomponent mixtures.     

Liquid–Liquid Equilibrium for Fuel Oxygenate Systems Containing Dialkyl Carbonate in Aqueous Solution

Experimental tie-line data were investigated for two quaternary systems of water + n-hexane + diethyl carbonate + dimethyl carbonate and water + toluene + isooctane + dimethyl carbonate, and two related ternary systems of water + n-hexane + diethyl carbonate and water + n-hexane + dimethyl carbonate at 298.15 K and ambient pressure. The experimental tie-line data have been correlated using a modified UNIQUAC model and an extended UNIQUAC model, both with multicomponent interaction parameters in addition to the binary ones.     

Selective dimerization of styrene to 1,3-diphenyl-1-butene by acetyl perchlorate

The linear unsaturated dimer of styrene, 1,3-diphenyl-1-butene, was obtained exclusively in the oligomerization of styrene by acetyl perchlorate in various solvents. In benzene, the linear dimer was produced in more than 90% yield at 50°C. In n-hexane and cyclohexane, the yield of the linear dimer was lower. The yield of the linear dimer was strongly dependent on the nature of solvent. When an increasing amount of 1,2-dichloroethane was added to benzene, the yield of the linear dimer gradually decreased. On the other hand, when a small amount of 1,2-dichloroethane was added to n-hexane or cyclohexane, the yield of the linear dimer increased. The yield of the linear dimer was almost independent of the reaction temperature and the initiator concentration. For comparison, the dimerization of α-methylstyrene was carried out, and the effects of the initiator and the solvent on the structure of dimers were investigated. On the basis of these results, the mechanism of the dimerization of styrene initiated by acetyl perchlorate is discussed.     

Excess Gibbs free energies and excess enthalpies for triethylamine + n-hexane,triethylamine + n-octane,and tributylamine + n-hexane at 298.15 K

Total vapour pressures have been measured by the isoteniscope method for triethylamine + n-hexane, triethylamine + n-octane, and tributylamine + n-hexane at 298.15 K. The excess Gibbs free energies G^E for the liquid phase have been calculated from the measurements; G^E is positive for the triethylamine systems and negative for the tributylamine system. The excess enthalpies H^E for these three mixtures and for tributylamine + n-octane have been measured at the same temperature. Except for tributylamine + n-hexane, all these H^E's are positive.     

Magnetic quenching of positronium in organic solutions

The magnetic quenching of ortho-positronium (o-Ps) in some pure nonpolar liquids (n-hexane, cyclohexane and benzene) and solutions (nitrobenzene in n-hexane, cyclohexane and benzene; and carbon tetrachloride and biphenyl in n-hexane) is examined for steady magnetic fields up to 14 kG by the positron annihilation lifetime technique. The long lifetime of o-Ps is very sensitive to the strength of the external magnetic field, decreasing as the field strength increases. This effect follows from a well-known principle of atomic physics, the quadratic Zeeman effect. With one exception, all the liquids studied here appear to be normal in this regard. The exception is nitrobenzene in n-hexane, which shows a very marked enhancement of quenching beyond the Zeeman effect at low fields.     

Mucoadhesive vaginal film of fluconazole using cross-linked chitosan and pectin

A series of silica gels (Si-40, Si-60, Si-100) and related carbon–silica gels, prepared by carbonization of CH₂Cl₂ at a surface of silica gels at 550 °C, characterized using FTIR/PAS, SEM/EDX, and nitrogen adsorption, was investigated upon interactions with polar (water, dimethylsulfoxide), weakly polar (chloroform), and nonpolar (n-hexane, n-decane, benzene, toluene) adsorbates using adsorption and differential scanning calorimetry methods. Features of confined space effects, such as freezing/melting point depression and melting delay, depend strongly on pore sizes, pore wall structure, type and amount of adsorbates, and the degree of pore filling. Melting curves of both polar and nonpolar adsorbates bound in broad pores (Si-60 and Si-100 based materials) can include two–three peaks around melting point, but for Si-40-based materials, a number of similar peaks is smaller. This occurs due to step-by-step melting of frozen structures located in broader pores and the absence of similar effects in narrower pores. The present study shows that complex carbon–silica gel adsorbents can be more effective adsorbents than simple silica gels due to the presence of a number of surface sites of various polarity and structure.

     

Polymerization of coordinated monomers. VI. Molecular complex formation of methyl methacrylate coordinated to stannic chloride with styrene or toluene

The equilibrium constants for the complex formation between stannic chloride and methyl methacrylate were determined in n-hexane–toluene solution at 0, ?20, and ?30°C by using the absorption band at 350 nm. Continuous variation plots at ?20°C in n-hexane based on the ¹H-chemical shifts definitely show a 1:1 interaction between the coordinated methyl methacrylate and styrene or toluene. The magnitudes of the shifts for the four groups of protons in methyl methacrylate are found to be in a specific ratio in common with the 1:2 complex–styrene or -toluene system. The equilibrium constants for the ternary molecular complex formation between the 1:2 complex and styrene or toluene were determined in n-hexane in the temperature range ?50 to +20°C by use of the chemical shifts. The concentrations of the complex species in the alternating copolymerization solutions were estimated by use of the equilibrium constants. There is a linear relationship between the enthalpy and the entropy changes for the ternary molecular complex formation, which is governed by the enthalpy factor. The specificity of the interactions indicates a specific time-averaged orientation of benzene ring to the coordinated methyl methacrylate. The effects of the coordination of methyl methacrylate to stannic chloride were discussed on the basis of results of ¹³C-NMR spectroscopy.     

Thermochemistry of Benzene Solution in Water-Aprotic Solvent Binary Mixtures

The enthalpies of solution of benzene in the mixed solvents water-1,4-dioxane, water-acetone, and water-dimethyl sulfoxide were determined in the entire ranges of their compositions at 25°C and compared with thermochemical characteristics of n-alkanes. Correlation dependences were obtained that allow one to describe the enthalpies of solution of benzene in the mixtures under study and to predict the corresponding values for other water-aprotic solvent mixtures.     

Peculiarities of asphaltene precipitation in <Emphasis Type="Italic">n</Emphasis>-alkane-oil systems

n-Pentane-, n-hexane-, and n-heptane-insoluble asphaltenes obtained via a standard procedure by precipitating from oil solutions in n-pentane, n-hexane, and n-heptane, respectively, as well as n-pentane/n-hexane/n-heptane-insoluble and n-heptane/n-hexane/n-pentane-insoluble asphaltene constituents prepared through successive washing (fractional dissolution) of n-pentane-insoluble asphaltenes with n-hexane and n-heptane and n-heptane-insoluble asphaltenes with n-hexane and n-pentane, respectively, are studied. Asphaltenes and their constituents extracted from three oils distinguished by high contents of asphaltenes, resins, and paraffins, respectively, are investigated by ¹H NMR spectroscopy in carbon tetrachloride solutions. It is established that the mass fractions and the fragment compositions of asphaltenes and their constituents depend on both the type of oil and the procedure of their preparation; i.e., the precipitation from n-alkane-oil systems or the extraction through the successive washing with a series of n-alkanes. The obtained experimental data made it possible to formulate a hypothesis according to which the precipitation of asphaltenes from oils is controlled by not only the dissolving power of a solvent with respect to molecular components of initial oils, but also (and primarily) by the dissolving power of a solvent with respect to supramolecular structures of asphaltenes formed in n-alkane-oil systems.     

Gaschromatographische Untersuchung der Adsorptionseigenschaften von Silicalit und ZSM-5

High silica molecular sieves (silicalite, ZSM-5) were tested as adsorbents for gas chromatographic trace analysis. Therefore the retention behaviour of low-boiling organic compounds (hydrocarbons, halogenated hydrocarbons, amines, alcohols and ethers) on these materials was investigated. The specific retention volumes at different temperatures have been determined and elution orders and peak shapes were studied. The retention data allow a simple calculation of the breakthrough volumes (dynamic adsorption capacity) and the chromatographic characterisation of the adsorbents. Both nitrogen and oxygen containing compounds could not—or at least unreproducibely—be eluated up to 300°. The elution order and the peak shape of compounds with the same number of carbon atoms but different geometric and electronic structure (e.g.n-butenes;n-hexane, cyclohexane, benzene) can be explained by the action of exclusion effects and different diffusion barriers. On the basis of calculated breakthrough volumes we conclude that silicalite should be useful in the preconcentration of both saturated C₃–C₆ hydrocarbons and C₁–C₂ chlorinated hydrocarbons from gaseous streams.