Tomasz Kościelski

β-cyclodextrin as a selective agent for the separation of o-,m- and p-xylene and ethylbenzene mixtures in gas-liquid chromatography

Abstract The dependence of the elution patterns of o , m - and p-xylenes and ethylbenzene on the β-cyclodextrin concentration in the formamide stationary phase deposited on Celite has been studied in the temperature range 50–70°C. It has been found that stereoselective molecular inclusion processes take place in the formamide medium, thus, modifying its chromatographic properties. Such systems result in a gain in stereoselectivity while at the same time retaining all the advantages of partition gas chromatography. The conditions for complete separation of the investigated compounds have been elaborated.

Catalytic reactions of hydrocarbons over PtPd alloys: III. Skeletal reactions of n-pentane and n-hexane over PtPdSiO2 catalysts

The isomerization, cyclization, and hydrogenolysis kinetics of n-pentane and n-hexane were studied on dispersed silica-supported 1% alloy consisting of 0-100% palladium/platinum. The catalysts were calcined for 25 hr at 600/sup 0/C prior to reduction or only reduced in hydrogen at 400/sup 0/C. The surface composition was probably similar to bulk composition. The catalytic activity vs. composition curves were similar for precalcined and uncalcined catalysts and for various reaction temperatures (300/sup 0/-360/sup 0/C). For n-pentane, hydrogenolysis was higher on palladium than on platinum or low-palladium alloys but more selective towards butane on platinum; isomerization decreased with increasing palladium content; and cyclization went through a maximum on alloy catalysts. The reaction patterns were similar with n-hexane, except that precalcination of the catalyst suppressed cyclization to methylcyclopentane and benzene. The catalysts underwent a poisoning process which was generally highest at the higher temperatures and higher palladium contents. The results were compared with results obtained on Pt-Pd foil and mechanisms were discussed.

Application of a gas-liquid chromatography system with α-cyclodextrin for monitoring the stereochemical course of β-pinene hydrogenation

SummaryComplete separation of a mixture containing two enantiomers of β-pinene and four stereoisomers of pinane was achieved by gas chromatography using α-cyclodextrin dissolved in formamide as the stationary phase. The developed method was utilized for the monitoring of the course of the catalytic hydrogenation of commercial (−)-β-pinene.

Gas-liquid chromatography system with α-cyclodextrin as an analytical tool for the studies of stereoselective hydrogenation of α-pinene

Summaryα-Cyclodextrin dissolved in formamide solution was applied as the stationary phase in gas-liquid chromatography for the enantio- and diastereoselective separation of α-pinene and pinanes. It was found that the stereoselectivity arising from inclusion of these compounds in α-cyclodextrin cavities is considerable. The method developed was used to monitor the stereochemical cource of α-pinene hydrogenation.

Catalytic reactions of hydrocarbons over Pt-Pd alloys: I. Skeletal reactions of C5 and C6 alkanes over Pt-Pd alloy films

Abstract The reactions of neopentane, n-pentane, and n-hexane in the presence of an excess of hydrogen have been studied on evaporated films of Pt-Pd alloys as catalysts. The selectivity in neopentane isomerization on a pure Pd film has been found to be nonnegligible, in contrast with previous work in the literature. A possible explanation of this involving the carbonization of the surface during the experiments and the effect of texture on the process is proposed. The neopentane isomerization vs alloy composition pattern is interpreted in terms of an “inferred” surface composition. The results may be easily explained assuming a one-Pt-site mechanism for isomerization and a two-Pd-site mechanism for hydrogenolysis. The 1,5-cyclization selectivity pattern in the n-pentane reaction is interpreted in terms of the change in active site number. In the n-hexane conversion the ratio of selectivity towards 1,6-versus 1,5-cyclization is higher for alloys than for pure metals.

Comparative studies of the chromatographic properties of α- and β-cyclodextrin in gas-solid and gas-liquid chromatography

Abstract A systematic study was carried out of the properties of α- and β-cyclodextrins as selective agents for the separation of various compounds, mainly isomers, in gas-liquid and gas-solid chromatographic systems. The test compounds included aliphatic and aromatic hydrocarbons (xylenes, trimethylbenzenes, diethylbenzenes) and alcohols (propanols, butanols). The possible interaction mechanism is discussed in terms of molecular inclusion, the effect of the nature of the matrix solvent on the chromatographic properties of the cyclodextrin solutions and the selectivity due to the inclusion process. Examples of chromatographic separations are given.

Resolution of cis- and trans-dimethylcyclohexanes by partition gas chromatography through cyclodextrin complexes

Abstract α- and β-Cyclodextrins, dissolved in formamide or ethylene glycol, were applied as stationary phases in gas chromatography for the resolution of isomeric cis- and trans-1,2-, 1,3-, and 1,4-dimethylcyclohexanes. It was found that stereoselectivity arising from inclusion of dimethylcyclohexanes in cyclodextrin cavities is more distinct for β-cyclodextrin. Of the two matrix solvents, which influence not only the capacity factors but also the separation factors, formamide is the more efficient medium for stereoselective cyclodextrin inclusion processes. An evaluation of stability constants of (β-cyclodextrin · dimethylcyclohexane) complexes was attempted. Almost complete separation of a mixture containing the six isomers investigated was achieved by using concentrated β-cyclodextrin (1.48 mol. %) in formamide solution.