Separation of unsaturated and aromatic hydrocarbons on capillary columns packed with barium sulphate

Summary Isomeric hydrocarbons with molecules having similar geometry but differing in the electron density distribution were separated on capillary columns packed with barium sulphate, a non-porous ionic adsorbent. Samples of BaSO₄ were washed free of foreign ions and modified by solutions of alkaline metal halides. The selectivity of the separation of unsaturated and aromatic hydrocarbons can be controlled by varying the conditions of the BaSO₄ treatment. Capillary columns packed with the ionic adsorbent were successfully used to separate all xylene and butene isomers, as well as isomers of cis and trans octene-2.     

Selective gas chromatographic separation of polycyclic aromatic hydrocarbons on Bentone 34

Summary Using modified Bentone 34 as a thin layer on glass beads in a short micropacked column at maximum working temperature reasonable retention times of polycyclic aromatic hydrocarbons were achieved up to perylene. Some differences in the elution order were observed as compared with other sorbents.     

Gas chromatographic separation of some labelled aromatic halogen compounds

Gas—liquid-chromatographic techniques for the separation of a large variety of mono-, di-and polysubstituted benzene derivatives from their multicomponent systems have been developed for the study of reactions of recoil halogen atoms with aromatic compounds. The¹⁸F,^34mCl,³⁸Cl,⁸²Br and¹²⁸I labelled benzene derivatives were produced by neutron irradiations of the corresponding liquid mixtures. Because of the short half-life of most of the isotopes in question a relatively fast method was required, therefore each of the techniques described takes less than one hour to achieve the separation.     

Thin-layer chromatographic separation and identification of some anions on copper sulphate impregnated silica gel layers

Summary Thin-layer chromatographic behaviour of thirteen anions on plain silica gel and silica gel impregnated with copper sulphate solution has been investigated in aqueous-organic solvents containing acetone, some of which have achieved reliable and reproducible separations. The effect of copper sulphate concentration on the mobility of anions has been examined. The results obtained on plain silica gel have been compared with those obtained on copper sulphate impregnated layers. The impregnated layers dramatically change the selectivity and permit separations not possible on untreated silica. Aqueous sodium chloride-acetone (9∶1) and ammonium hydroxide-acetone (9∶1) were the most effective solvent systems for differential migration of anions. Better results in terms of clarity of detection and compactness of spots were found with HCOOH-acetone as compared to HCl-acetone. The effect of anion loading on R_F values has been investigated and identification limits on impregnated layers determined.     

Interpretative optimization and artificial neural network modeling of the gas chromatographic separation of polycyclic aromatic hydrocarbons

An interpretative strategy (factorial design experimentation+total resolution analysis+chromatogram simulation) was employed to optimize the separation of 16 polycyclic aromatic hydrocarbons (PAHs) (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, benzo(a)anthracene, benzo(k)fluoranthene, benzo(b)fluoranthene, benzo(a)pyrene, indeno(1,2,3-c,d)pyrene, dibenzo(a,h)anthracene, benzo(g,h,i)perylene) in temperature-programmed gas chromatography (GC). Also, the retention behavior of PAHs in the same GC system was studied by a feed-forward artificial neural network (ANN). GC separation was investigated as a function of one (linear temperature ramp) or two (linear temperature ramp+the final hold temperature) variables. The applied interpretative approach resulted in rather good agreement between the measured and the predicted retention times for PAHs in both one and two variable modeling. The ANN model, strongly affected by the number of input experiments, was shown to be less effective for one variable used, but quite successful when two input variables were used. All PAHs, including difficult to separate peak pairs (benzo(k)fluoranthene/benzo(b)fluoranthene and indeno(1,2,3-c,d)pyrene/dibenzo(a,h)anthracene), were separated in a standard (5% phenyl-95% dimethylpolysiloxane) capillary column at an optimum temperature ramp of 8.0 degrees C/min and final hold temperature in the range of 260-320 degrees C.     

Headspace solvent microextraction and gas chromatographic determination of some polycyclic aromatic hydrocarbons in water samples

Headspace solvent microextraction (HSME) was shown to be an efficient preconcentration method for extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample solutions. A microdrop of 1-butanol (as extracting solvent) containing biphenyl (as internal standard) was used in this investigation. Extraction occurred by suspending a 3 μl drop of 1-butanol from the tip of a microsyringe fixed above the surface of solution in a sealed vial. After extraction for a preset time, the microdrop was retracted back into the syringe and injected directly into a GC injection port. The effects of nature of extracting solvent, microdrop and sample temperatures, stirring rate, microdrop and sample volumes, ionic strength and extraction time on HSME efficiency were investigated and optimized. Finally, the enrichment factor, dynamic linear range (DLR), limit of detection (LOD) and precision of the method were evaluated by water samples spiked with PAHs. The optimized procedure was successfully applied to the extraction and determination of PAHs in different water samples.     

Circular dichroism of some crowded cyclic olefins

Chiroptical data for sterically crowded olefins, i.e. cholest-5-enes and cholest-6-enes substituted in the 6- or the 4,4,6-positions suggest that the π-σ^* transition may precede the olefinic π-π^* transition. A comparison with short-wavelength Cotton effects in structurally related enones and dienes is also presented.     

Calorimetric studies of adsorption of aromatic hydrocarbons on silicalite

Conclusions Complex relationships between the differential adsorption heats and the degree of filling are observed when benzene and toluene are adsorbed on silicalite. A possible reason for this phenomenon is either a redistribution or a reorientation of the adsorbed molecules when the degree of filling exceeds 0.5.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2820–2823, December, 1982.The authors express their gratitude to Dr. Fahlke for synthesizing and supplying the silicalite sample.     

The use of thin-layer chromatography in investigations of the adsorption of some aromatic hydrocarbons

Summary Using adsorption TLCR_M values were measured for six aromatic hydrocarbons on silica gel G. The following binary mobile phases were used: trichloroethylene+benzene, carbon tetrachloride+benzene, n-heptane+trichloroethylene and n-heptane+benzene. The obtained results are presented graphically and compared with values calculated theoretically. Generally a good agreement was found in the R_M values calculated and measured. This confirms the applicability of Ocik's equation descrbed earlier in the examination of interactions between the components of adsorption systems. The analysis of the variations of various parameters of the equation can supply important data concerning these interactions.     

Optimization of micellar liquid chromatographic separation of polycyclic aromatic hydrocarbons with the addition of second organic additive

The micellar liquid chromatographic (MLC) separations of polycyclic aromatic hydrocarbons (PAHs) were optimized for three micellar systems, cetyltrimethylammonium chloride (CTAC), dodecyltrimethylammonium chloride (DTAC), and sodium dodecylsulfate (SDS), with 1-pentanol as the only organic additive. A difference in the separation was observed between CTAC and SDS/DTAC. Under each optimized separation conditions, CTAC-modified mobile phase provides the least desirable separation, which is attributed to its longer carbon tail (C16 vs. C12). In addition to 1-pentanol, the main organic additive, a second organic additive (3% 1-propanol) in the micelle-modified mobile phase was found to enhance the resolution of PAH chromatographic peaks. However, the extent of the enhancement varies for the different micellar systems, with the greatest resolution improvement seen for CTAC, and little effect for shorter-tail SDS and DTAC. This study shows the potential use of second organic additive (1-propanol), to the main nonpolar additive (1-pentanol), in facilitating the MLC separation of larger nonpolar compounds.     

Friedel-crafts cyanation of some reactive aromatic hydrocarbons

Direct cyanation, using the heterogeneous Friedel-Crafts system cyanogen bromide/aluminium chloride, has given good yields of the following carbonitriles: anthracene-9-, chrysene-6-, 2-methyl-1-naphtho-, 4-methyl-1-naphtho-, 1-naphtho-, phenanthrene-9-, 2,4,6-trimethylbenzo-, triphenylene-1- and triphenylene-2-carbonitriles.     

Selective transformation of light olefins into aromatic hydrocarbons over pentasil zeolites

1-Pentene and 1-hexene transformation into aromatic hydrocarbons over H-ZSM-5, H-ZBS-11 and H-ZSM-11 modified with Zn(II), Ga(III), Mn(II) and Fe(III) has been studied. Aluminosilicate zeolites exhibited higher activity than borosilicate zeolites. Zn-species are effective in dehydrogenation, generating allylic intermediates from olefins used as feed.     

Calculated polarizabilities for some aliphatic and aromatic hydrocarbons

Ground-state molecular polarizabilities of some aliphatic and aromatic hydrocarbons have been calculated using the method of Marchese and Jaffé. The polarizability components for the typical normal alkane n-heptane are found to be very nearly independent of conformation; those for biphenyl show a significant dependence but the average polarizability is approximately constant. The polarizabilities of the n-alkanes in general are seriously underestimated, but relatively good agreement with experiment is obtained for benzene and biphenyl.