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Query: CAS:142-82-5 (heptane)
 3,094 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In organic chemistry, hydrocarbon compounds with one to four carbon atoms are given individual names such as methane, ethane, propane and butane, whereas those with five carbons or more are named by the serial Greco-Roman numerals like pentane pente, 5), hexane hex, 6 (and heptane hepta, 7). The author points out a distinct conceptual break between the numbers four and five. There have been arguments that primitive cultures had numerals only up to four, and a quantum mental leap was required to cross the boundary after four. Linguistic discussions are made to substantiate the break by scrutinizing the spellings of the numbers "five", "eight" and "nine" of the proto-Indo-European language. In ancient Roman times, 1 (children's ages were counted by winters up to four and by years from five on, 2 (the first four calender months had real names and after four they were called by serial numbers, (3) children up to the fourth were given individual names but from the fifth child on they were named by serial number words, and (4) the words of the number of times had a sharp break between four and five. In various Indo-European languages long ago, the numbers one through four were inflected adjectives, while the numbers beyond four were non-inflectable. All the above observations indicate an existence of a conceptual break after the number four. The author concludes that the notion of such break latently survived in peoples' minds for a long time and came to light when naming of the hydrocarbons was attempted in the 19th century.
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PMID:A distinct break between butane and pentane. 1162 69

Air samples, representing indoor environments of a kitchen in which a kerosene stove was used were collected and analysed for volatile organic compounds (VOCs) viz., n-hexane, benzene, heptane, toluene, p- and o-xylene and n-decane using a cryogenic preconcentration system and a gas chromatograph with a flame-ionisation detector. Simultaneous outdoor samples were also collected to determine indoor to outdoor (I/O) ratios for each compound. Reversed phase high performance liquid chromatography (HPLC) with ultra violet absorption detection was optimised for separation and quantification of polycyclic aromatic hydrocarbons (PAHs) in air particulate matter. Concentration of total suspended particulate matter (TSPM), benzene soluble organics and the PAHs in air samples collected in indoor environment of some tenements at Trombay, Mumbai where kerosene is used as cooking fuel are discussed in relation to the concentration of the same in outdoor environment in vicinity of the tenement. VOCs and PAHs results from samples collected in kitchens in Trombay are discussed in relation to indoor air pollution.
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PMID:Monitoring of indoor volatile organic compounds and polycyclic aromatic hydrocarbons arising from kerosene cooking fuel. 1171 93

In an attempt to elucidate the molecular basis for concentration (isotherm) effects on retention in gas-liquid chromatography, configurational-bias Monte Carlo simulations in the Gibbs ensemble were carried out to investigate changes in analyte partitioning caused by overloading a model chromatographic system with either an alkane or an alcohol. Squalane was used as the stationary-phase material, and the analytes included n-pentane, n-hexane, n-heptane, 1 -butanol, and 1-pentanol. Three systems were studied that differed in the mobile-phase composition: (i) a helium vapor, (ii) a n-hexane vapor, and (iii) a 1-pentanol-saturated helium vapor. While the amount of helium that partitions into the stationary phase is very small, both n-hexane and 1-pentanol partition strongly into and thereby swell the stationary phase. Although the swelling of the stationary phase leads to a reduction in the partition coefficients for the alkane solutes for both the n-hexane- and 1-pentanol-swollen stationary phases, the effects on the alcohol solutes differ markedly. Whereas saturation by n-hexane causes a decrease of the alcohol partition contants (to an extent similar to that for the alkane solutes), the saturation by 1-pentanol causes a dramatic increase of the alcohol partition coefficients; e.g., the Kovats index of 1-butanol increases by more than 150 Kovats units. The formation of hydrogen-bonded alcohol aggregates in the liquid phase is the microscopic origin for the dramatic effect of 1-pentanol saturation on the retention of alcohols.
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PMID:Influence of analyte overloading on retention in gas-liquid chromatography: a molecular simulation view. 1179 13

Two new orthohydroxy Schiff bases, 7-phenylsalicylidene benzylamine (PSBA) and 7-ethylsalicylideneaniline (ESA) have been synthesized. The excited state intramolecular proton transfer (ESIPT) and the structure of PSBA and ESA in its crystalline form and in the solvents n-hexane, n-heptane and 1,4-dioxane have been investigated by means of absorption, emission and nanosecond spectroscopy at room temperature and 77K. One ground state species has been detected both in neutral and basic solutions of both PSBA and ESA: the cis-enol form with an intramolecular hydrogen bond. The ESIPT and formation of keto tautomer are evidenced by a large Stokes shifted emission (approximately 12000 cm(-1)) at room temperature only in the case of ESA. On the other hand the keto tautomer is the predominant species at 77K in a solid matrix and as a solid sample at room temperature both in the case of ESA and PSBA. In the case of both ESA and PSBA the more intense, higher energy emission is due to the species which has not undergone ESIPT and attributed mainly due to cis-enol form. The trans-enol form is also observed by changing the excitation wavelength. Both the compounds are found to undergo a structural change to a zwitterionic and intermolecular hydrogen bonded form in the presence of a strong base like triethylamine. From the nanosecond measurements and quantum yield of fluorescence we have estimated the decay rates of proton transfer reaction in the case of PSBA. Our theoretical calculation at the AM1 level of approximation shows that the ground singlet state has a rather large activation barrier both in the case of PSBA and ESA. The barrier height is much lower on the corresponding excited singlet surface only in the case of ESA. The process is predicted to be endothermic in the ground state and exotherrmic in the excited singlet state.
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PMID:Excited state proton transfer reaction of two new intramolecularly hydrogen bonded Schiff bases at room temperature and 77K. 1180 46

Using chiral HPLC and 13C NMR analyses, the optical purity of (+)-spiro[3.3]heptane-2,6-dicarboxylic acid (1) obtained by the known diastereomer method with brucine was first clarified to be 90% e.e., which was conventionally considered to be 100% e.e. Among the ester derivatives synthesized, dicinnamyl spiro[3.3]heptane-2,6-dicarboxylate (2) was found to show high optical separation ability on the chiral HPLC with cellulose phenyl carbamate stationary phase eluting with hexane/2-propanol (10/1, v/v) at a flow rate of 0.4 ml/min at 35 degrees C (separation factor, a, 1.14), and the isolated optically pure (+)- and (-)-2 show [alpha]D26 of + 1.84 degrees (c = 1.74, CHCl3) and -1.84 degrees (c = 1.74, CHCl3), respectively. Acidic hydrolysis of optically pure (+)-/(-)-2 without racemization yielded optically pure (+)-/(-)-1, exhibiting [phi]405(270 = + 21.1 degrees ([phi]D27 = +9.1 degrees) (c = 5.33, acetone) and [phi]405(27) = -21.1 degrees ([phi]D27 -9.1 degrees) (c = 5.32, acetone), respectively.
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PMID:Enantiopure spiro[3.3]heptane-2,6-dicarboxylic acid. 1204 46

Experiments and molecular simulations were carried out to study temperature effects (in the range of 323 to 383 K) on the absolute and relative retention of n-hexane, n-heptane, n-octane, benzene, toluene and the three xylene isomers in gas-liquid chromatography. Helium and squalane were used as the carrier gas and retentive phase, respectively. Both the experiments and the simulations show a markedly different temperature dependence of the retention for the n-alkanes compared to the arenes. For example, over the 60 K temperature range studied, the Kovats retention index of benzene is found to increase by about 16 or 18+/-10 retention index units determined from the experiments or simulations, respectively. For toluene and the xylenes, the experimentally measured increases are similar in magnitude and range from 14 to 17 retention index units for m-xylene to o-xylene. The molecular simulation data provide an independent method of obtaining the transfer enthalpies and entropies. The change in retention indices is shown to be the result of the larger entropic penalty and the larger heat capacity for the transfer of the alkane molecules.
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PMID:Temperature effects on the retention of n-alkanes and arenes in helium-squalane gas-liquid chromatography. Experiment and molecular simulation. 1205 2

Several models have been published for calculating blood-air, tissue-air, or tissue-blood partition coefficients of volatile organic chemicals in human or rat tissues, from functions of their octanol-water partition coefficients or solubilities in vegetable oil and water. In this work, the relative accuracy, strengths, and limitations of the various models are examined. Comparison of predicted human tissue-air and tissue-blood partition coefficients with experimental values has been made for 12 chemicals, covering a wide range of lipophilicity (acetone, isopropanol, diethylether, methylene dichloride, benzene, toluene, trichloroethylene, trichloroethane, n-pentane, cyclohexane, n-hexane, and n-heptane). Seven published models for human tissue-air and 10 models for tissue-blood partition coefficients have been compared. Fewer models are available for predicting rat tissue-air and rat tissue-blood partition coefficients, but a similar comparison has been made. The ratio of predicted to experimental partition coefficients and their mean, R(mean), and the mean magnitude of the difference between predicted and experimental values of log(10) P, E, were used to assess the accuracy of each model. For the test set the most accurate for human blood-air partition coefficients were the empirical equations of Meulenberg and Vijverberg (R(mean) = 1.1 +/- 0.46, E = 0.156) and the empirical solvation equation of Abraham and Weathersby (1994) (R(mean) = 0.93 +/- 0.38, E = 0.166). For rat blood, predictions are much less accurate due to difficulties in modeling the effects of protein binding, which are much larger. Overall, for rat blood-air partition coefficients the equation of Meulenberg and Vijverberg (1999) (R(mean) = 0.74 +/- 0.50, E = 0.236) was the most accurate. The tissue-composition-based equations of Poulin and Krishnan, using solubilities in vegetable oil, performed well for human liver-air partition coefficients (R(mean) = 1.21 +/- 0.28, E = 0.079) for log(octanol-water partition coefficients) > 0.7 and for fat-air partition coefficients, but overestimated solubilities in human kidney and brain tissues (e.g., for kidney tissue, R = 1.88 +/- 0.58, E = 0.255). The equations of Meulenberg and Vijverberg (2000a), Abraham and Weathersby (1994), and Paterson and Mackay (1989) also performed moderately well for human tissue-air partition coefficients. For rat muscle-air, liver-air, and fat-air partition coefficients the model of Poulin and Krishnan (1996a) gave the most accurate predictions. For tissue-blood partition coefficients, generally good agreement with experimental values is obtained by the empirical model of Balaz and Lukacova (1999) (e.g., for human kidney, R(mean) = 1.15 +/- 0.38, E = 0.085) and, if solubility in fat is known, by the equations of Fiserova-Bergerova and Diaz (1986) (e.g., for human muscle, R(mean) = 1.10 +/- 0.39, E = 0.107). The equations of DeJongh et al. (1997) gave the most accurate predictions for rat muscle-blood, liver-blood and fat-blood partition coefficients (e.g., for rat muscle R(mean) = 1.03 +/- 0.39, E = 0.149), but predictions were less accurate than for human tissue-blood partition coefficients, attributable to difficulties in modeling the effect of protein binding. The choice of equation for use in physiologically based pharmacokinetic (PBPK) models depends on the species, tissue, and chemical lipophilicity.
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PMID:Comparison of models for the estimation of biological partition coefficients. 1213 36

The importance of adsorption at the gas-liquid interface on retention in gas-liquid chromatography has been controversial since the pioneering work of Martin in the 1960s. In particular, experimental studies using chromatographic and static techniques to quantify partitioning and adsorption of polar analytes on nonpolar liquid phases yielded conflicting results. In this work, Monte Carlo simulations were carried out for a free-standing liquid slab of squalane surrounded by a helium vapor to investigate interfacial adsorption effects for n-pentane, n-hexane, n-heptane, 1-butanol, and benzene solutes at infinite dilution. The simulations indicate preferential adsorption for the flexible alkane and alcohol solutes in a narrow region just inside the Gibbs dividing surface, but no such effect was observed for the rigid benzene solute. Nevertheless, the extent of the interfacial enrichment is small, as measured by the partition coefficient between the bulk liquid and the interfacial region (K(bulk-interface) approximately 1.5). In addition, a region that is slightly depleted for all solute molecules is found to separate the interfacial and bulk regions of the squalane slab. Thus, adsorption at the gas-liquid interface should not contribute significantly to the retentive behavior observed in gas-liquid chromatography on nonpolar capillary columns but might play a role in packed-bed columns with low bonded-phase loadings. The origin for the small enrichments and more favorable free energies for solutes at the interface is that the enthalpies of solvation decrease to a smaller relative extent than the entropies of solvation compared to the bulk liquid.
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PMID:Molecular simulation of concurrent gas-liquid interfacial adsorption and partitioning in gas-liquid chromatography. 1213 63

In Japan, disposable gloves made from nitrile-butadiene rubber (NBR) are frequently used in contact with foods. In a previous paper, we investigated substances migrating from various gloves made of polyvinyl chloride, polyethylene, natural rubber and NBR. Zinc di-n-butyldithiocarbamate (ZDBC), diethyldithiocarbamate (ZDEC) used as vulcanization accelerators, di(2-ethylhexyl)phthalate (DEHP) used as a plasticizer and many unknown compounds that migrated from NBR gloves into n-heptane were detected by GC/MS. In this paper, six unknown compounds were obtained from one kind of NBR glove by n-hexane extraction and each was isolated by silica gel chromatography. From the results of NMR and mass spectral analysis of the six unknown compounds, their structures are proposed as 1,4-dione-2,5-bis(1,1-dimethylpropyl)cyclohexadiene (1), 2-(1,1-dimethylethyl)-4-(1,1,3,3-tetra methylbutyl)phenol (2), 2,6-bis(1,1-dimethylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (3), 2,4-bis(1,1,3,3-tetramethylbutyl)phenol (4), 2-(1,1-dimethylethyl)4,6-bis(1,1,3,3-tetramethylbutyl)phenol (5) and 2,4,6-tris(1,1,3,3-tetramethylbutyl)phenol (6). Compound 1 was observed in five of the seven kinds of NBR gloves, and compounds 2-4 and 6, which are not listed in Chemical Abstract (CA), were present in four kinds of gloves.
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PMID:Isolation and identification of some unknown substances in disposable nitrile-butadiene rubber gloves used for food handling. 1245 82

For the membrane-based separation of benzene/cyclohexane mixtures, the pervaporation properties of different 6FDA (4,4'-hexafluoroisopropylidene diphthalic anhydride) based copolyimide membranes have been investigated. In order to obtain high permeability as well as high selectivity copolyimides were synthesised using a combination of 4MPD (2,3,5,6-tetramethyl-1,4-phenylene diamine) and 6FpDA (4,4'-hexafluoro-isopropylidene dianiline) as well as DABA (3,5-diaminobenzoic acid) as monomers. Cross-linking is possible with this type of copolyimides and necessary to reduce swelling effects, which often occur with polymeric membranes and lead to a deterioration of the separation characteristics in aromatic/aliphatic separation processes. In order to find the most suitable membrane material, the polymer structure, the crosslinking agents, as well as the crosslinking methods have been varied. The separation characteristics have been determined by sorption and pervaporation experiments. Sorption experiments have been carried out at 60 degrees C using benzene, toluene and ethylbenzene as aromatic components and cyclohexane, cyclohexene, hexane and heptane as aliphatic solvents. Pervaporation experiments have been performed at 60 degrees C using benzene/cyclohexane mixtures with benzene concentrations covering the whole concentration range. It has been found that crosslinked copolyimide membranes show excellent chemical resistance, strongly reduced swelling behaviour and higher selectivity in aromatic/aliphatic separation compared to conventional membrane materials.
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PMID:Polymeric membranes for aromatic/aliphatic separation processes. 1246 84


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