Showing papers on "Hexane published in 1998"
TL;DR: The solvent dependence of the steady-state and time-resolved fluorescence emission from the S2 (11Bu) state of all-trans-β-carotene was investigated in a range of polar and nonpolar solvents and in hexane/carbon disulfide mixtures as mentioned in this paper.
Abstract: The solvent dependence of the steady-state and time-resolved fluorescence emission from the S2 (11Bu) state of all-trans-β-carotene was investigated in a range of polar and nonpolar solvents and in hexane/carbon disulfide mixtures. The steady-state absorption and fluorescence emission maxima in both polar and nonpolar solvents showed parallel shifts with increasing solvent polarizability, indicating that the emitting state is the S2 (11Bu) state. The lifetime of the S2 state was determined using the fluorescence upconversion technique, and lifetimes varying from 120 fs in quinoline to 177 fs in hexane were found. An intramolecular relaxation process occurring on a similar time scale was observed as a broadening in the reconstructed time-dependent emission spectra in hexane and as emission wavelength-dependent lifetimes in all the solvents studied. Correlations were observed between the S2 lifetimes, the π* solvatochromic parameter, and the ratio of the absorption fine structure. A correlation between the ...
180 citations
TL;DR: In this paper, the isomerization of n-hexane over Pt-loaded H-β zeolites was investigated, and it was shown that 1-hexene produced by the dehydrogenation of hexane at the metal component is not directly involved in the reaction.
85 citations
TL;DR: In this article, a method was developed to determine the total phospholipid content in vegetable oil by Fourier transform infrared spectroscopy (FTIR), which was found to be a useful analytical tool for simple and rapid quantitative determination.
Abstract: A method was developed to determine the total phospholipid content in vegetable oil by Fourier transform infrared spectroscopy (FTIR). Calibration curves of I-α-phosphatidylcholine (PC), I-α-phosphatidylethanolamine (PE), and I-α-phosphatidylinositol (PI) in hexane were generated at different concentrations. The optimal phospholipid absorption bands between 1200–970 cm−1 were identified and used for quantitative determination. High R
2≥0.968 were observed between band areas and phospholipid standard concentrations. Phospholipids from crude soybean oil were obtained by water degumming, and purification was performed on a silicic acid column. The phospholipid contents of purified phospholipid extract, degummed and crude soybean oil determined from calibration equations were >90, 0.0113, and 1.77%, respectively. High correlations of determination (R
2≥0.933) were observed between the FTIR method and thin-layer chromatography-imaging densitometry method for the determination of phospholipid content. FTIR was found to be a useful analytical tool for simple and rapid quantitative determination of phospholipids in vegetable oil.
65 citations
TL;DR: Addition of alcohol, especially isopropyl alcohol, to the micellar organic phase enabled the backward extraction of cytochrome c to be achieved without the formation of insoluble aggregates.
35 citations
35 citations
TL;DR: In this article, a method of measuring the distribution of polymer segments at a liquid/liquid interface using neutron reflection was developed, which consists of forming a stable hexane layer on top of an aqueous subphase so that two interfaces contribute to the measured reflectivity.
Abstract: We have developed a method of measuring the distribution of polymer segments at a liquid/liquid interface using neutron reflection. The method consists of forming a stable (1–4 μm) hexane layer on top of an aqueous sub-phase so that two interfaces contribute to the measured reflectivity. This has been done by condensing vapour onto the surface in an accurately temperature-controlled environment. The neutron reflectivity was measured at four angles of incidence on the SURF reflectometer. The attenuation of the reflectivity from the lowest angle is used to determine the thickness of the hexane layer. A series of poly(ethylene oxide) poly(propylene oxide) ABA block copolymers adsorbed at the hexane/water interface have been investigated. Since the polymers were hydrogenous, measurements were made with D 2 O as the aqueous phase and with either null reflecting hexane or 60% D-hexane as the oil phase in order to obtain adequate contrast. The polymer volume fraction profile has been determined by simultaneous fits to the data from these combinations of solvent contrasts. It was found that there was a good correlation between the molar mass of the poly(ethylene oxide) block and the thickness of the polymer layer in the aqueous phase and that the chains were stretched beyond their radii of gyration expected for bulk solution.
35 citations
TL;DR: In this article, it was shown that photolysis of 1,1-diphenylgermene in hexane, acetonitrile, or tetrahydrofuran gives rise to the formation of a transient, assignable to the germene on the basis of its second-order decay kinetics, UV spectrum (λmax = 325 nm), and the fact that it is quenched by adding alcohols and acetic acid.
Abstract: Direct irradiation of 1,1-diphenylgermetane in hexane solution affords 1,1,3,3-tetraphenyl-1,3-digermetane in high chemical yield. Photolysis in the presence of aliphatic alcohols leads instead to the formation of the corresponding alkoxymethyldiphenylgermane. These results are consistent with the formation of 1,1-diphenylgermene as a primary photochemical product from photolysis of the germetane. Nanosecond laser flash photolysis of the compound in hexane, acetonitrile, or tetrahydrofuran gives rise to the formation of a transient, assignable to the germene on the basis of its second-order decay kinetics, UV spectrum (λmax = 325 nm), and the fact that it is quenched by addition of alcohols and acetic acid. Absolute rate constants for reaction of 1,1-diphenylgermene with methanol, ethanol, 2-propanol, tert-butyl alcohol, acetic acid, the O-deuterated isotopomers, and acetone were determined in the three solvents, using the germetane as the precursor. The kinetics and mechanisms of these germene trapping r...
34 citations
TL;DR: Densities, viscosities, and refractive indexes of the ternary system {x 1 propyl propanoate + x 2 hexane + (1 − x 1 − x 2) benzene} and of the corresponding binary mixtures {x1 propyl polyanoate+ x 2 h...
Abstract: Densities, viscosities, and refractive indexes of the ternary system {x1 propyl propanoate + x2 hexane + (1 − x1 − x2) benzene} and of the corresponding binary mixtures {x1 propyl propanoate + x2 h...
33 citations
TL;DR: In this article, the experimental results of pyrene dissolved in six binary mixtures containing 2-butanol with hexane, heptane, octane, cyclohexane, methylcyclohexanes, and 2,2,4-trimethylpentane at T =299.15 K were used to test two mathematical representations based upon the combined Nearly Ideal Binary Solvent (NIBS)/Redlich-Kister equation and Modified Wilson model.
33 citations
TL;DR: In this paper, a continuous flow apparatus was used both to minimize possible thermal degradation and to accurately measure the lower hexadecanol concentrations in the vapor phase, where the addition of the hydroxyl group to the C16 hydrocarbon backbone significantly affects phase behavior with hexane.
Abstract: Vapor and liquid equilibrium compositions have been measured for the hexane + hexadecane and the hexane + 1-hexadecanol systems at temperatures from 472.0 K to 623.0 K and pressures from 6.2 bar to 46.4 bar. A continuous-flow apparatus was used both to minimize possible thermal degradation and to accurately measure the lower hexadecanol concentrations in the vapor phase. Mixture critical pressures and compositions were also measured. Results indicate that the addition of the hydroxyl group to the C16 hydrocarbon backbone significantly affects the phase behavior with hexane.
31 citations
TL;DR: Er2Ti4O2(OEt)18(HOEt)/Et=C2H5 was derived by single-crystal X-ray diffraction, showing the unit cell to have the monoclinic space group symmetry,P21/n, and the lattice constantsa=15.180(2) A,b=12.693(2), A,c=16.602(3), A andβ=98.91(1)° and to contain two formula units as discussed by the authors.
TL;DR: In this paper, the preparation and properties of the acid catalysts obtained by grafting zirconium and silicon alkoxides and ZIRconium-sulfated alkoxide on γ-alumina were studied.
Abstract: In this work, the preparation and properties of the acid catalysts obtained by grafting zirconium and silicon alkoxides and zirconium-sulfated alkoxide on γ-alumina were studied. The catalysts prepared were examined with electrochemical techniques to evaluate the hydroxyl density, the ZPC (zero point charge) and the intrinsic surface ionization constants. The catalysts were also submitted to TPD (temperature-programmed desorption) analysis using different organic bases to determine the distribution of acid sites. Some samples were also submitted to microcalorimetric analysis using pyridine as probe molecule, and to XPS measurements. Finally, the catalysts prepared were tested in three different reactions: methanol dehydration, n -hexane isomerization and cracking and skeletal isomerization of 1-butene to isobutene. The most relevant results obtained were: (i) grafted zirconia strongly promoted methanol dehydration up to an upper limit of grafting; (ii) grafted zirconium sulfated alkoxide showed a moderate activity, but good selectivity in n -hexane isomerization; (iii) silicated aluminas (prepared in the absence of solvents) showed high activity, selectivity and stability in the 1-butene skeletal isomerization reaction.
TL;DR: In this article, the N 4 ligand in Co(III) N 4 (aq) complexes at pH 6.5 towards hydrolysis of the above nerve agent simulants was found to be trpn > (tn 2 ) > (en 2 ) (trpn = tris(3-aminopropyl)amine, tn = trimethylenediamine, en-ethyleniamine).
TL;DR: The activity, selectivity and coupling efficiency of alkane oxidation by the monooxygenase enzyme cytochrome P450cam can be enhanced by engineering the active site topology to accommodate different alkanes.
Abstract: The activity, selectivity and coupling efficiency of alkane oxidation by the monooxygenase enzyme cytochrome P450cam can be enhanced by engineering the active site topology to accommodate different alkanes: reducing the active site volume by the Y96F–V247L double mutations resulted in four-fold higher activity for the oxidation of hexane (1) than 3-methylpentane (2) while the larger active site of the Y96A–V247A double mutant gave rise to a two-fold preference for 2 over 1.
TL;DR: The combined use of chemical manganese dioxide (CMD) and molecular sieves in hexane (or in acetone) in general or CMD alone in particular cases enables the convenient and efficient oxidation of benzylic and allylic alcohols, phenols and amines under relatively mild conditions.
Abstract: The combined use of chemical manganese dioxide (CMD) and molecular sieves in hexane (or in acetone) in general or CMD alone in particular cases enables the convenient and efficient oxidation of benzylic and allylic alcohols, phenols and amines under relatively mild conditions
TL;DR: In this paper, a phase transition from a monolayer to a condensed molecular packing is observed, either from the molecules lying flat to orienting themselves upright or from a mono-to a bilayer.
Abstract: Ellipsometric investigations of alkane adsorption from saturated alkane vapor show that hexane and heptane wet the air/water interface with a closed ultrathin film of molecular thickness that is topped with droplets of micrometer dimensions. Octane adsorbs only in a submonolayer film. Brewster angle microscopy and the analysis of the time evolution of the ellipsometric signal of the hexane and heptane adsorption reveal phase transitions; i.e., the alkane films are below their critical temperatures. In the course of the adsorption first the formation of a monolayer with low (gaseous) molecular density is observed. Then a first-order phase transition to a condensed molecular packing occurs. After completion of this condensed monolayer, another transition is observed, either from the molecules lying flat to orienting themselves upright or from a mono- to a bilayer. Depending on the molecular orientation, the molecular packing density in the condensed films is either approximately the same as the liquid bulk density (if the molecules are oriented upright) or it is about 120% of the liquid bulk density (if the molecules lie flat). Ultimately the mono- and/or bilayer is topped with droplets of several micrometers diameter.
TL;DR: In this paper, limiting activity coefficients were measured in 10 binary systems of the type alcohol + solvent at temperatures between 293 K and 333 K. The results were carried out with a newly built headspace gas chromatograph.
Abstract: As part of a project on thermodynamic properties of hydrogen-bonding solutions, limiting activity coefficients were measured in 10 binary systems of the type alcohol + solvent at temperatures between 293 K and 333 K. The systems are: methanol + tetrachloromethane, ethanol + hexane, ethanol + heptane, ethanol + cyclohexane, ethanol + tetrachloromethane, 2-methylpropan-2-ol (tert-butyl alcohol) + hexane, 1-hexanol + hexane, 1-hexanol + cyclohexane, 1-hexanol + tetrachloromethane, and 1-hexanol + toluene. Furthermore, new experimental results are reported on the vapor−liquid equilibrium for the system ethanol + heptane at 313 K. The measurements were carried out with a newly built headspace gas chromatograph.
TL;DR: In this paper, the partition coefficient of 41 substances (several phenol, indole, biphenyl, and naphthalene derivates, polycyclic aromatic compounds, and polyfunctional haloaromatics) in hexane + water at 298.15 K were reported.
Abstract: Experimental results for the partition coefficient of 41 substances (several phenol, indole, biphenyl, and naphthalene derivates, polycyclic aromatic compounds, and polyfunctional haloaromatics) in hexane + water at 298.15 K are reported. Partition coefficients were measured by reversed phase high-performance liquid chromatography and the shake-flask method. The experimental results are compared successfully to predictions by the linear solvation energy relationship method.
TL;DR: In this paper, the Tsonopoulos correlation equation was used to correlate the experimental data and optimally fitted binary parameters were presented, including an azeotropic point for the binary mixture of cyclohexane + 2-butanol.
Abstract: Vapor−liquid equiliibria were measured at 101.3 kPa for three binary mixtures of 2-butanol + butyl acetate, hexane + butyl acetate, and cyclohexane + 2-butanol. The isobaric T−x−y data were reported, including an azeotropic point for the binary mixture of cyclohexane + 2-butanol. Calculations of the nonideality of the vapor phase were made with the second virial coefficients determined by the Tsonopoulos correlation equation. Various activity coefficient models were used to correlate the experimental data. Satisfactory results were obtained, and optimally fitted binary parameters are presented.
TL;DR: In this article, a vacuum electromicrobalance cell was used to measure the equilibrium data of nine binary solvent + polymer systems, including hexane, pentane, water, methanol, and ethanol.
Abstract: Vapor liquid equilibrium data of nine binary solvent + polymer systems were measured by a vacuum electromicrobalance cell. Solvents used were hexane, pentane, water, methanol, and ethanol. Polymers tested were poly(dimethylsiloxane), Mn, 26 000; poly(propylene oxide), Mn, 2000; poly(vinyl alcohol), Mn, 88 000; poly(acrylic acid), Mn, 1 250 000; and polycarbonate, Mn, 24 000. Measured equilibrium data were tabulated and discussed.
TL;DR: The thermodynamics of the lipase-catalyzed stereospecific esterification of 1-dodecanoic acid with (−)-menthol in seven organic solvents have been investigated as discussed by the authors.
Abstract: The thermodynamics of the lipase-catalyzed stereospecific esterification of 1-dodecanoic acid with (−)-menthol in seven organic solvents have been investigated. Equilibrium measurements were performed using hexane, heptane, cyclohexane, toluene, 2,2,4-trimethylpentane, acetonitrile, and 2-methyl-2-butanol at the temperature T = 298.15 K. The equilibrium constants have been correlated with the (octanol + water) partition coefficients and the relative permittivities of the solvents. The saturation molalities and the (hexane + water) partition coefficients of (−)-menthol, 1-dodecanoic acid, and (−)-menthyl dodecanoate have also been determined at T = 298.15 K. The equilibrium constant of the esterification reaction in aqueous media has been calculated. An important finding is that the molality of water plays an important role in determining the extent of ester formation. In acetonitrile and 2-methyl-2-butanol, which have a very high molality of water, the formation of (−)-menthyl dodecanoate is considerably ...
TL;DR: In this paper, the production of an esterase by Fusarium oxysporum, grown on tomato skins as the sole carbon source, was studied in submerged and solid state cultures.
TL;DR: In this article, the suitability of tetraethylene glycol as a high-boiling solvent for the separation of m-cresol from neutral oils was evaluated and the effect of parameters such as solvent ratios on the desired separation were investigated.
Abstract: Coal pyrolysis liquors are a major source of valuable phenolic compounds. In this study, the separation of m-cresol from neutral oils by means of liquid−liquid extraction is investigated. Liquid−liquid equilibria for the systems m-cresol + o-toluonitrile + hexane + water + tetraethylene glycol + undecane + dodecane and m-cresol + o-toluonitrile + hexane + water + tetraethylene glycol have been determined at 313.15 K in order to evaluate the suitability of tetraethylene glycol as a high-boiling solvent for the separation of m-cresol from neutral oils. The effect of parameters such as solvent ratios on the desired separation were investigated. These are illustrated on the basis of separation factors, percentage of feed o-toluonitrile remaining in the solvent phase, and percentage recovery of m-cresol. From the experimental results it was concluded that tetraethylene glycol is suitable for the proposed separation. The nonrandom two-liquid model fitted the experimental data satisfactorily. The model was used ...
TL;DR: In this article, the ways of preparation of the linear hexane hydroisomerization catalysts on the base of mordenite-clinoptilolite rocks of Ukrainian deposits are described.
Abstract: The ways of preparation of the linear hexane hydroisomerization catalysts on the base of mordenite–clinoptilolite rocks of Ukrainian deposits are described: under the strictly defined conditions of thermic and acidic treatments of parent rocks, followed by palladium (0.5 wt%) introduction, the samples of catalysts were synthesized which are well comparable with the catalysts on the base of synthetic mordenite. The high efficiency of the samples synthesized was achieved due to the appropriate degrees of the residual crystallinity of the mordenite–clinoptilolite rocks modified as well as due to the corresponding strong acidic sites content of their zeolitic components. The isomerization mechanism through the hexane molecules protonation resulting in the formation of non-classic carbonium ions, which include the pentacoordinated carbon atoms, with subsequent dehydrogenation of these structures over Lewis acidic sites is proposed – the role of Lewis acids play probably palladium and extraframework aluminum. Based on the consideration of the different proton affinity of various C 6 H 14 isomers, the plausible pathways to the formation of definite hexane isomers are discussed. These routes give such sets of individual branched hexanes which consist both the thermodynamically predicted and really found isomerizate compositions.
TL;DR: In this paper, isomerizations of n -pentane and n -hexane were carried out in the presence of hydrogen over Cs 2.5 H 0.5 PW 12 O 40 (Cs2.5) promoted with Pt by direct impregnation and mechanical mixing, and results were compared with similarly Pt-promoted H-ZSM-5 and sulfated zirconia.
Abstract: Isomerizations of n -pentane and n -hexane were carried out in the presence of hydrogen over Cs 2.5 H 0.5 PW 12 O 40 (Cs2.5) promoted with Pt by direct impregnation and mechanical mixing, and the results were compared with similarly Pt-promoted H-ZSM-5 and sulfated zirconia. The mechanical mixture of Pt/Al 2 O 3 and Cs2.5 showed the highest stationary activity and selectivity and the least deactivation for both reactions at a relatively low temperature (453 K) and a low H 2 pressure (pentane:H 2 :N 2 =0.05:0.05:0.9, hexane:H 2 :N 2 =0.05:0.2:0.75).
TL;DR: In this article, the best predictive equation was found to predict the observed solubility data to within an overall average deviation of about 3% using numerical values of 125 cm 3 mol −1 and 175 cm 3mol −1 for the anthracene-alcohol and pyrene-alcohol stability constants, respectively.
Patent•
25 Jun 1998TL;DR: In this paper, azeotrope-like compositions of 1-bromopropane and at least one organic solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-pro-panol and 2-methyl-2-propane are described.
Abstract: The invention relates to novel compositions of 1-bromopropane and at least one organic solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, 2,2,2-trifluoroethanol, tetrahydrofuran, nitromethane, ethyl acetate, acetonitrile, hexane, 1,3-dioxolane, 1-chloro-2-methylpropane, 1,1,1,2,3,4,4,5,5, 5-decafluoropentane, methyl ethyl ketone and cyclohexane and more particularly to azeotrope-like compositions based on these compounds which are useful as solvents in refrigeration flushing, oxygen system cleaning and vapor degreasing applications.
TL;DR: In this article, a split-mode capillary gas chromatographic procedure is developed for the analysis of nine solvents commonly used in the synthesis and purification of bulk pharmaceuticals.
Abstract: A direct-injection, split-mode capillary gas chromatographic procedure is developed for the analysis of nine solvents commonly used in the synthesis and purification of bulk pharmaceuticals. The nine solvents are methanol, methylene chloride, hexane, ethyl acetate, tetrahydrofuran, iso-octane, 1,4-dioxane, toluene, and dimethylformamide. The procedure is derived by modifying U.S. Pharmacopeia and European Pharmacopeia compendial methods. Modifications include raising injection temperature and revising temperature programming, leading to enhanced sensitivity and a shorter analysis time of 40 min. For each solvent, the procedure is validated for selectivity, linearity, recovery, precision, quantitation limit, and detection limit. All nine solvents are completely resolved. Determination coefficients (r 2 ) are at least 0.998. Toluene has a linear response from 10 to 1000 ppm (with respect to a drug concentration of 100 mg/mL). All other solvents have linear responses from 20 to 2000 ppm. Recoveries range from 99.3 to 100.9%. Relative standard deviations for precision are not more than 2.8%. The quantitation limits (in ppm) are as follows: methanol, 8.6; methylene chloride, 95.3; hexane, 48.5; ethyl acetate, 23.5; tetrahydrofuran, 13.0; isooctane, 24.0; 1,4-dioxane, 31.5; toluene, 10.0; and dimethylformamide, 14.9. Furthermore, a system suitability test is validated, and requirements are set. Finally, two drug substance samples are analyzed to show the suitability of the procedure, which can generally be used to determine any one or any combination of these nine residual solvents in water-insoluble bulk pharmaceuticals.
TL;DR: The structural transformations of the C-70 in benzene, toluene, and hexane solutions were studied in this article, using X-ray powder diffraction experiments made directly on the c-70 solution samples.
Abstract: The structural transformations of the C-70 in benzene, toluene, and hexane solutions were studied. The X-ray powder diffraction experiments made directly on the C-70 solution samples showed structural transformations of similar types for all the tested so