Showing papers on "Hexane published in 1977"

Interactions in alkane systems by depolarized Rayleigh scattering and calorimetry. Part 1.—Orientational order and condensation effects in n-hexadecane + hexane and nonane isomers

Abstract: Molecular optical anisotropies (γ2) have been obtained from depolarized Rayleigh scattering experiments on the 5 hexane isomers and 15 nonane isomers of widely varying degrees of branching. Values of γ2 have also been obtained for these molecules at high dilution in carbon tetrachloride. The latter values reflect the anisotropies of the molecular shapes of the isomers while the pure state values also contain a contribution due to correlation of the orientations of neighbouring molecules. Thus, for highly branched, isotropic isomers, the pure and dilute solution γ2 values are the same and are small. With increasing molecular anisotropy, the pure state value increases more rapidly than the dilute, the divergence reflecting the increasing correlation of molecular orientations. Values of γ2 have been found for n-hexadecane at high dilution in the hexanes and nonanes. They increase with the anisotropy of the solvent molecules and yield increasing values of the J12 parameter, which characterizes the correlation of orientations of the n-hexadecane and solvent molecules. The J12 values are given approximately by the geometric mean, (J11J22)½, of the order parameters of the pure liquids, indicating that the mixing of two liquids results in a net destruction of orientational order, i.e., ΔJ12=½(J11+J22)–J12 is positive. This change explains the variation in the heats of mixing of n-C16+ hexane systems. Molar heats of mixing have been measured at 25°C through the concentration range for n-C16 with 21 nonane isomers. With increasing nonane branching, ΔhM increases proportionally to ΔJ12. However, when nonane isomers have high degrees of steric hindrance, e.g., 3,3-diethylpentane or 2,3,3,4-tetramethylpentane, a new and large negative contribution is encountered in ΔhM. For example, ΔhM for n-C16+ 3,3-diethylpentane is S-shaped and negative at high nonane concentrations. Values of ΔvM and ΔsM also contain negative contributions for the few systems studied. The effect resembles a “condensation” of the less hindered alkane onto the large sterically hindered nonane, similar to the condensation effect found in cholesterol + lipid systems.

Vibration Spectra and Rotational Isomerism of Chain Molecules. II. Butane, Pentane, Hexane, Pentane-d12, and Hexane-d14

Abstract: The Raman spectra of butane, pentane, hexane, pentane-d12, and hexane-d14 and infrared spectra of pentane-d12 and hexane-d14 were measured for the liquid and solid states. The rotational isomerism of normal paraffins was studied on the basis of the spectral observations and the normal coordinate calculations. The spectra of the deuterated compounds were useful in the confirmation of the less stable isomers and the establishment of the local symmetry force field of normal paraffins. The enthalpy differences among the rotational isomers were studied on pentane and hexane, which yielded some important data for the study of the conformations and properties of longer hydrocarbons.

Interactions in alkane systems by depolarized Rayleigh scattering and calorimetry. Part 2.—Orientational order in systems containing hexadecane isomers of different structure

Abstract: Depolarized Rayleigh scattering has been used to obtain values of the molecular optical anisotropy (γ2) for the following hexadecane isomers at high dilution in carbon tetrachloride : 2,2,4,4,6,8,8-heptamethylnonane, 6-, 4- and 2-methylpentadecane, 6-pentylundecane and n-hexadecane. The values increase moderately through the series corresponding to increasingly anisotropic molecular shapes. Values of γ2 have also been obtained for the hexadecane series in their pure liquid states. These increase rapidly relative to the dilute solution values, indicating the development of short-range orientational order or correlations of molecular orientations. The pure liquid results with 6-, 4- and 2-methylpentadecane show that orientational order depends strongly on the methyl position and length of the straight-chain part of the alkane molecule. Values of γ2 for the hexadecane isomers have been found for high dilution in cyclohexane, 2,2-dimethylbutane and n-hexane which indicates that the hexadecanes can correlate their orientations to only a limited extent with these hexane solvents. Heats of mixing have been measured at 25°C through the concentration range for the hexadecane isomers mixed with cyclohexane, 2,2-dimethylbutane and n-hexane. For each hexane, the heats increase through the series of hexadecane isomers. This corresponds to the increase of orientational order in the pure hexadecane isomers and the destruction of order in the hexadecane on mixing with the hexane. The magnitudes and concentration dependences of the heats for the n-C6+ C16 isomer systems are similar to those for n-C6+ n-C16 heats at different temperatures. This is explained by changing temperature having the same effect on the order of n-C16 as changing molecular shape on the order of the C16 isomers at 25°C.

Photoreactions of 1- and 2-naphthonitriles with tetramethylethylene in various solvents

Abstract: The photoreactions of 1- and 2-naphthonitriles with tetramethylethylene have been studied in the solvents hexane, benzene, dimethoxyethane, methanol, and acetonitrile. In hexane, benzene, or dimeth...

Butyl ester preparation for gas-liquid chromatographic determination of fatty acids in butter

Abstract: Butter oil is extracted from butter with hexane, using a rolling boil technique. The resulting 10% butter oil in hexane is converted to butyl esters, using butanol in place of methanol as specified in the official final action method, 28.063-28.067. A water wash and centrifuge technique is used to remove butanol from the n-hexane-butyl ester solution. Conversions to butyl esters are quantitative by the boron trifluoride, sulfuric acid, and sodium butoxide procedures. When methyl ester methods are used, there are serious losses of the short chain volatile and water-soluble acids, making the methyl ester procedures questionable for determining the authenticity of milk fat.

Oat Oil: Refining and stability

Abstract: Oil obtained by petroleum ether extraction of Dal oats was refined by conventional methods. Degumming loss was reduced to 15% by degumming in hexane solution and partially neutralizing the oil with sodium hydroxide. The free fatty acid was 6~8%, and alkali refining losses were 25~30%. Oat oil was bleached successfully with charcoal and deodorized. Stability of the refined oil was compared with soybean oil at 25 and 55 C by peroxide values and organoleptic tests. Stability of oat oil was increased by the addition of citric acid and was significantly greater than that of soybean oil, especially at 25 C. Oat oil contained significant amounts of α-tocopherol, but ferulic and caffeic acids, antioxidants important in whole oats, were not extracted by hexane.

Determination of pentane formed during autoxidation of oils contained in solid samples

Abstract: A convenient and practical technique for the measurement of pentane formed during peroxidation of solid materials containing unsaturated oils was developed. The test has a sensitivity below. 1. parts per million (ppm) and can be used to monitor shelf-life of a variety of products. A special glassware was designed to perform a single extraction-concentration step. The pentane is recovered in 2 ml of hexane and analyzed by gas chromatography. This method correlates well with taste panel scores.

Comparison of the values of the interaction parameter ξ from upper critical solution temperatures of acetone + alkanes with values obtained from gas-liquid critical temperatures

Abstract: The upper critical solution temperatures, UCST , of acetone + alkane (n- C5H12 to n-C17H36) and acetone + hexane isomers have been measured. These results are used to calculate an interaction parameter ξ by using the van der Waals one-fluid model together with the Guggenheim equation of state. Values of ξ are compared with those obtained from the gas-liquid critical temperatures. The gas-liquid critical temperatures for the n- alkane + acetone systems were taken from the literature whereas those for the hexane isomers + acetone were measured in this work. The values of ξ calculated from gas-liquid critical temperatures are slightly greater than those calculated from the UCST as has been observed previously for other systems.

Determination of residual hexane in solvent extracted meals

Abstract: A simple modification of the volitilization procedure improved the reproducibility and covered a wide range of residual hexane in meal with good precision. A comparison study showed that the modified volatilization method released and assayed more residual hexane from the meals than did the direct gas chromatographic technique.

Effects of post‐curing of unsaturated polyester resins in various media

Abstract: Experimental studies were performed on the effects of postcuring of' styrenated, unsaturated polyesters in nitrogen gas, water or its vapor, hexane vapor, dimethyl sulfoxide (DMSO), and dirnethyl formamide (DMF) all at 100°C It was found that, nitrogen gas and water are inactive, hexane acts as a chain transfer agent, and DMF and DMSO behave as solvents which extract residual styrene monomer and anhydrides from the resins. Post-treatment in inert media can result in further reaction leading to more complete cure as free radicals and residual monomer continue to react. The post-curing reaction is a radical copolymerization. Further condepgation polymerisation does not occur. Post-curing in, hexane vapor1eads to a transfer of the active sites from the radicals to the hexane and to no further radical polymerization.

1,3,6-Tris(4,6-diamino-1,3,5-triazine-2-yl)hexane

Abstract: 1,3,6-Tris(4,6-diamino-1,3,5-triazine-2-yl)hexane, and a flame retardant resin composition comprising (A) about 5 to about 100 parts by weight of 1,3,6-tris(4,6-diamino-1,3,5-triazine-2-yl)hexane and (B) 100 parts by weight of a thermosetting resin or a thermoplastic resin.

Photochemistry of 1,2-diphenylcyclobutene in protic solvents. Addition of alcohols, acetic acid, and water.

Abstract: Irradiation of 1,2-diphenylcyclobutene (1) in methanol affords the methyl ethers, 1,2-diphenyl-1-methoxycyclobutane (2a) and 1-(α-methoxybenzyl)-1-phenylcyclopropane (3a). In acetic acid and in a mixture of water and dioxane, the corresponding esters (2b and 3b) and alcohols (2c and 3c) are formed, respectively. Evidence supporting the involvement of a singlet species was obtained upon finding that the fluorescence of 1 is substantially quenched upon the addition of methanol or acetic acid to a solution of 1 in hexane.

Ion-solvent and ion-ion interactions: alkali metal tetraalkylaluminates in nonaqueous solutions

Abstract: The use of the alkali metal tetraalkylaluminates offer a unique approach to the study of ion-solvent and ion-ion interactions in non-aqueous media. Because of their solubility in nonpolar solvents such as hexane and benzene, they permit the observation of specific ion-solvent interactions without interference from the solvent. Their general application to the study of solvation numbers, ion-pair types, and ionic aggregation are discussed.