Showing papers on "Hexane published in 1990"
TL;DR: In this article, a molecular dynamics simulation of the interface between liquid hexane and liquid water has been performed, and the interface was found to be about 10 O(n) wide, which is inconsistent with the known solubility of hexane in water and is believed to be an artifact of the intermolecular potentials used.
Abstract: A molecular dynamics simulation of the interface between liquid hexane and liquid water has been performed. The sample consisted of a two-phase system comprising 187 hexanes and 1,200 waters, confined to a box measuring 83.19 {times} 30.1 {times} 30.1 A{sup 3}. A total of 94.4 ps was simulated (60 ps of equilibration and 34.4 ps of analysis). The interface was found to be about 10 {angstrom} wide. It does not appear to be molecularly sharp. A small number of hexane molecules are detached, i.e., completely surrounded by water. This is inconsistent with the known solubility of hexane in water and is believed to be an artifact of the intermolecular potentials used. Differences between the interfacial and bulk liquids were observed. Water is more structure in the interfacial region than in bulk, and hexane molecules in the interfacial region were found to exhibit an excess of trans conformations relative to bulk. Neither component displays any preferential orientation with respect to the lab frame.
104 citations
TL;DR: Stability of the lipase has been proved to be correct and similar in both solvents and inhibition by ethanol excess has been found but is greater in n-hexane, which can explain the higher initial velocities obtained in supercritical carbon dioxide for the highest ethanol concentrations.
Abstract: Oleic acid esterification by ethanol has been performed by an immobilized lipase fromMucor miehei in supercritical carbon dioxide and in n-hexane as solvents. In both media, determination of apparent kinetic constants has been achieved and influence of water content has been shown to be different due to various rates of water solubilities. Stability of the lipase has been proved to be correct and similar in both solvents. Inhibition by ethanol excess has been found but is greater in n-hexane. That can explain the higher initial velocities obtained in supercritical carbon dioxide for the highest ethanol concentrations.
100 citations
TL;DR: Chymotrypsin powder suspended in organic solvents in the presence of Na 2 CO 3.10H 2 O catalyses peptide synthesis from X-Ala-Phe-OMe and Leu-NH 2 (X = Boc or Z) as mentioned in this paper.
59 citations
TL;DR: In this paper, a mechanism consisting of 156 free-radical reactions is used to model the experimental results, obtained in a previous study, of the pyrolysis of supercritical hexane in the 290-365 o C and 210-15600 bar temperature and pressure ranges.
Abstract: A mechanism consisting of 156 free-radical reactions is used to model the experimental results, obtained in a previous study, of the pyrolysis of supercritical hexane in the 290-365 o C and 210-15600 bar temperature and pressure ranges. The Arrhenius parameters used here are very close to those measured in the gas phase. Strong arguments support the extrapolability of this reaction mechanism to the lower temperatures of geochemical interest. Simulations performed between 60 and 200 o C show that, at these low temperatures, pressure has little effect on the distribution of hexane pyrolysis products. The main effect is that high pressure considerably decreases the overall pyrolysis rate of hexane
55 citations
TL;DR: In this article, high-performance liquid chromatography of the concentrated phospholipids was accomplished on a Lichrosorb Si-60 10 μ column, 250×4.6 mm with ultraviolet detection at 206 nm.
Abstract: Damage to soybeans due to pre-harvest stress, storage, and export shipment has been related to an increase in the nonhydratable phospholipid content of crude oil. Phospholipids in crude soybean oil extracted from such distressed soybeans have been analyzed by gradient high-performance liquid chromatography. Crude oil was fractionated by solid phase extraction using sequential elution for recovery of phosphatides. High-performance liquid chromatography of the concentrated phospholipids was accomplished on a Lichrosorb Si-60 10 μ column, 250×4.6 mm with ultraviolet detection at 206 nm. A 20-min solvent gradient of 2-propanol/hexane/water (42∶56∶2, 51∶38∶11) gave retention profiles of phospholipid distribution (major subclasses) that changed with impact of stress applied to plant or seed. Soybeans stored at high moisture levels (16% and 20% moisture) for up to 28 days yielded oils having phosphorus contents which decreased in direct relationship to days of storage. Retention profiles were unusable for fractions isolated from oils with phosphorus content below 100 ppm. Data show that during progressive damage, the content of phosphatidylcholine and phosphatidylinositol decreased while the phosphatidic acid content increased.
48 citations
TL;DR: The results in binary systems have been correlated by using the classical equation for solid-liquid solubility and the activity coefficients correlated by means of three equations that describe the Gibbs excess free energy of mixing, G E : the equations of Wilson, UNIQUAC, and NRTL.
Abstract: The solubilities of 2-benzoyl-1-naphtol, 1-benzoyl-2-naphthol, and 4-benzoyl-1-naphthol have been determined experimentally in pure hexane and 1-butanol and in seven mixtures of hexane and 1-butanol by a dynamic method from 285 to 330 K. Systems of 2-benzoyl-1-naphthol with mixed solvent were found to exhibit the synergetic effect of solubility. The results in binary systems have been correlated by using the classical equation for solid-liquid solubility and the activity coefficients correlated by means of three equations that describe the Gibbs excess free energy of mixing, G E : the equations of Wilson, UNIQUAC, and NRTL. In ternary systems, the values of activity coefficients have been predicted by the Wilson, UNIQUAC, and NRTL equations. The solvent-solvent parameters were obtained from literature VLE data
34 citations
TL;DR: In this paper, the effects of solvents on oil paint films were examined using gas chromatography and combined GC/mass spectrometry, and the amount of extracted oil components and changes in weight, thickness, color and gloss varied with the solvent, pigment, time of contact and the age of the sample.
Abstract: This article examines the effects of solvents on oil paint films. Samples of oil paint films five, 10 and 50 years of age, containing lead white, raw sienna, vermilion or a red azo dye as pigments, were exposed to the solvents hexane, toluene, acetone and ethanol. The solvent extracts were analyzed by gas chromatography and combined gas chromatography/mass spectrometry. Changes in weight, thickness, color and gloss were measured. Much of the extracted material consisted of free saturated fatty acids. Small amounts of free unsaturated fatty acids and their degradation products were also present. Other materials such as wax and resin were present in some samples. Synthetic dyes were easily extractable when present. The amount of extracted oil components and changes in weight, thickness, color and gloss varied with the solvent, pigment, time of contact and the age of the sample. Toluene, acetone and/or ethanol produced the greatest changes. Samples containing lead white, which catalyzes the drying re...
29 citations
TL;DR: In this article, an equilibrium study on the solvent extraction of copper(II) with 5-dodecylsalicylldoxime, the active component of LIX 860, was carried out at 303 K to clarify the effects of the organic diluent and the aqueous media, together with measurements of the apparent molecular weight and solubility of the extractant.
28 citations
TL;DR: (1-Phenyl-2,3,4,5,tetramethyl-1-germacyclopentadienyl)lithium (4) was prepared by reaction of 1-phenyl 2.3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22) with n-butyllithium in THF/hexane at -70 °C and chemically identified by electrophilic
28 citations
Patent•
12 Dec 1990TL;DR: The phase transfer catalysts of 1,6-bis (penta-n-butylguanidinium) hexane dibromide are obtained by reaction of a tetraalkyl urea with phosgene or phosphorus oxychloride, or by the reaction of tetra-alkyl thiourea with an N-N-diaalkyl carbamoyl halide, to yield a chloroformamideinium salt, then reaction of said salt with a monoalkylamine and reaction of the resulting pentaalk
Abstract: α,ω-Bis(pentaalkylguanidinium) alkane salts such as 1,6-bis (penta-n-butylguanidinium) hexane dibromide are prepared by the reaction of a tetraalkyl urea with phosgene or phosphorus oxychloride, or by the reaction of a tetraalkyl thiourea with an N-N-diaalkylcarbamoyl halide, to yield a chloroformamideinium salt, followed by reaction of said salt with a monoalkylamine and reaction of the resulting pentaalkylguanidinium salt with an alkylene dihalide. Said salts are useful as phase transfer catalysts.
26 citations
TL;DR: In this paper, a static method has been used to measure the venture pressure of (n -hexane + n -hexadecane), (n-hexane+ n -octane), and (n − octane + N -hexadesane) at 298.15 K. The results have been fitted using a polynomial and agreement within experimental error was obtained.
TL;DR: In this article, an aluminium oxide film sensor (Endress & Hauser type DY20B) was used for continuous monitoring and control of water activity during lipase-catalysed esterification in a hexane medium: water formed as a reaction product was removed by controlled recirculation of the headspace gases through a drying column.
TL;DR: In this paper, coal was extracted with different solvents of boiling range from 65 °C (hexane) to 330-350°C (liquid paraffin) and the minimum extractability of coal was observed in hexane and maximum in anthracene oil.
TL;DR: The inhibitory effects of their sodium salts for the platelet aggregation induced by arachidonic acid with rabbit platelet-rich plasma and platelet aggregating induced by collagen with rat washed platelets were examined.
Abstract: Thromboxane A2 receptor antagonists 11a, 15a, 26a, 30a, 34a, 36a, 46a, 52a, 61a, 72a, and 82a, which contain 6-oxabicyclo[3.1.0]hexane, 6-thiabicyclo[3.1.0]hexane, bicyclo[3.1.0]hexane, or 6,6-dimethylbicyclo[3.1.0]hexane ring systems with heptenoic and (phenylsulfonyl)amino side chains, and their corresponding sodium salts and methyl esters were synthesized. This study then examined the inhibitory effects of their sodium salts for the platelet aggregation induced by arachidonic acid with rabbit platelet-rich plasma and platelet aggregation induced by collagen with rat washed platelets.
TL;DR: Etude de l'influence de the addition of dodecanol sur la tension interfaciale d'une solution aqueuse de dodecylsulfate de sodium a l'interface eau/hexane.
Abstract: Etude de l'influence de l'addition de dodecanol sur la tension interfaciale d'une solution aqueuse de dodecylsulfate de sodium a l'interface eau/hexane
TL;DR: In this article, a spent hydrotreating catalyst was submitted to soxhlet extraction using dichloromethane, hexane and benzene, which showed a better extraction performance than benzene.
TL;DR: In this paper, a gas chromatographic analysis of headspace and peroxide values of oil samples was performed to determine the oxidative stability of soybean oils obtained by different extraction solvents such as hexane, water and Folch's solvent.
Abstract: Oxidative stabilities of crude soybean oils obtained by different extraction solvents such as hexane, water and Folch's solvent (mixture of two volumes of chloroform and one volume of methanol) were determined by gas chromatographic analyses of headspace and peroxide value of oil samples. For the determination of oxidative stability of oil samples, total volatile compounds formation, molecular oxygen disappearance in the headspace and peroxide value of oil samples were measured. Iodine value (133–136), saponification value (195–198), unsaponifiable matters (0.3–0.4%), iron (0.6 ppm), sterols content (2,400–2,590 ppm), tocopherols content (1,250–1,520 ppm) and fatty acid composition of crude oils obtained by different solvent extraction were not significantly different. Acid value of Folch-extracted oil was the highest as 1.3, whereas those of hexane-and aqueous-extracted oils were 0.5 and 0.4, respectively. Crude soybean oil extracted by Folch's method was found to contain the most phosphorus, while hexane- and aqueous-extracted oils contained similar amounts of phosphorous. Crude soybean oil obtained by Folch extraction was most stable in oil oxidation, and oxidative stabilities of oils obtained by hexane and aqueous extraction, which were significantly much less stable than Folch-extracted oil, were not significantly different during ten weeks storage.
TL;DR: In this article, phase equilibrium measurements on (methanethiol or ethanetiol or propan-1-thiol or butan- 1-THI + n -hexane or n -decane or toluene or water) have been made on a static system, at mole fractions 0 to 0.2 of thiol over a temperature range of 323 to 373 K.
TL;DR: In this article, a tri(2-methoxyphenyl)phosphine has been prepared in an excellent yield by metallating methoxybenzene with n-BuLi.
TL;DR: In this article, the reaction rate constants of positronium with nitrobenzene have been determined in hexane and benzene solutions as a function of external pressure up to 1000 kg/cm 2.
TL;DR: A Tian-Calvet-type calorimeter was used to determine excess enthalpies, H E, as a function of concentration at atmospheric pressure and 298.15 K for some binary liquid mixtures containing linear alkanenitriles of the general formula CH 3 (CH 2 ) n−2 CN (n=2, 3, 4, 5) with n-alkanes (hexane, heptane) or cyclohexane as discussed by the authors.
Abstract: A Tian-Calvet-type calorimeter was used to determine excess enthalpies, H E , as a function of concentration at atmospheric pressure and 298.15 K for some binary liquid mixtures containing linear alkanenitriles of the general formula CH 3 (CH 2 ) n−2 CN (n=2, 3, 4, 5) with n-alkanes (hexane, heptane) or cyclohexane
TL;DR: In this paper, the Flory theory with an interchange energy parameter, which is a quadratic function of the number of carbon atoms in the alkane molecule, provides a satisfactory correlation of the results.
TL;DR: In this paper, a series of measurements of integral n-hexane vapor sorption at 25°C and moderate activity, in polystyrene microspheres of varying radii, exhibits typical non-Fickian behavior: nonoverlap of curves of fractional uptake versus (square root of time)/radius.
Abstract: A series of measurements of integral n-hexane vapor sorption at 25°C and moderate activity, in polystyrene microspheres of varying radii, exhibits typical non-Fickian behavior: nonoverlap of curves of fractional uptake versus (square root of time)/radius. The data are examined in light of a sorption isotherm indicating hexane solubility in excess of that predicted by the Flory–Huggins equation, up to the hexane activity at which the glass transition apparently occurs. A transport analysis is developed based on the assumption that below the transition temperature Tg the rate of sorption is limited by the rate of polymer chain relaxations induced by the penetrant, which facilitate hexane entry into, and immobilization in, glassy microvoids.
TL;DR: In this paper, the isotherms of n -hexane and methyl iodide on fibrous carbon material (FCM), both uncoated and coated with 5% w/w triethylene diamine (TEDA), were determined in the temperature span from 303 to 318 K using gas-chromatographic technique.
TL;DR: Des solubilites mutuelles liquide liquide pour des melanges binaires constitues d'ammoniac and d'un alcane sont mesurees pour des temperatures allant jusqu'a la temperature critique de la solution as discussed by the authors.
Abstract: Des solubilites mutuelles liquide liquide pour des melanges binaires constitues d'ammoniac et d'un alcane sont mesurees pour des temperatures allant jusqu'a la temperature critique de la solution
TL;DR: In this article, the rate constants for the decay of ultraviolet fluorescence from liquid butane, pentane, and hexane have been measured as a function of temperature between their respective freezing points and near room temperature.
Abstract: The rate constants for the decay of ultraviolet fluorescence from liquid butane, pentane, and hexane have been measured as a function of temperature between their respective freezing points and near‐room temperature. The rate constants are well characterized as the sum of an activated and nonactivated term, as has been described previously. The parameters determining the rate constants are evaluated. Relative fluorescence quantum yields are also measured over the same temperature range. Normalization of the relative fluorescence quantum yields with absolute quantum yields measured previously at 195 K renders the relative determinations absolute. A comparison of the fluorescence results with the photochemical yields shows that a fraction of the initially formed upper excited states dissociates mainly into radicals, in competition with internal conversion to the fluorescing state.
TL;DR: In this article, it is shown that phenoxyphenol and hexyloxybenzene are produced as precursors to the observed products, and that positive ion scavengers inhibit the reactivity.
TL;DR: In this paper, the interfacial tension between hexane solution of cholesterol and water was measured as a function of temperature and the mole fraction of cholesterol in hexane under atmospheric pressure.
Abstract: The interfacial tension between hexane solution of cholesterol and water was measured as a function of temperature and the mole fraction of cholesterol in hexane under atmospheric pressure. The interfacial tension vs. mole fraction of cholesterol curve was observed to have two break points at a certain temperature; the concentration of the break point increases with increasing temperature. The experimental results were analyzed by applying the rigorous thermodynamics of adsorption at interfaces developed previously. The excess number of moles of cholesterol and the thermodynamic quantity changes associated with its adsorption were found to show the discontinuous changes at the break points. It was concluded that the first-order phase transition takes place from the gaseous to the expanded state and from the expanded to the condensed one in the adsorbed film of cholesterol at the hexane/water interface.
TL;DR: In this article, an alumina-supported nickel catalysts have been prepared by controlling the initial pH level of Ni(NO 3 ) 2 solution prior to impregnation.
Abstract: Alumina-supported nickel catalysts have been prepared by controlling the initial pH level of Ni(NO 3 ) 2 solution prior to impregnation. The various pH levels used were pH 3, 5, 6, and 8.3. Studies were carried out by performing catalytic cracking of n-hexane in a fixed bed reactor at 733 K and atmospheric pressure. The characterization of prepared catalysts and the carbon content of used ones were analyzed by using X-ray diffraction, temperature-programmed desorption temperature-programmed hydrogenation of the carbon deposit, and chemical analysis for carbon