Raymond N. Castle

Isolation of sulphur heterocycles from petroleum- and coal-derived materials by ligand exchange chromatography

Abstract A rapid method for the isolation of sulphur heterocycles (PASH) from the aromatic fraction of complex mixtures is described, based on ligand exchange column chromatography using silica gel impregnated with palladium chloride. The application of the procedure to a coal liquid and petroleum heavy ends yielded sulphur fractions composed of PASH having two to six aromatic rings. The fractions were examined by capillary column gas chromatography with flame ionization and flame photometric detection, and by gas chromatography-mass spectrometry.

Mutagenic activity of methyl-substituted tri- and tetracyclic aromatic sulfur heterocycles.

A number of polycyclic aromatic sulfur heterocycles have been identified in coal-derived products and in shale oils. The mutagenic activity of some of these compounds, including dibenzothiophene, benzo[b]naphtho[1,2-d]thiophene, benzo[b]naphtho[2,1-d]thiophene and benzo[b]naphtho[2,3-d]thiophene have been determined using the Salmonella/microsome mutagenicity test. These compounds demonstrated either very weak or no mutagenic activity. The methyl derivatives of each of these four compounds were assayed for mutagenic activity. Salmonella typhimurium TA98 was used as the tester strain. All assays required a rat-liver homogenate metabolic activator. Five of the methylated derivatives, 1-methylbenzo[b]naphtho[1,2-d]thiophene, 3-methylbenzo[b]naphtho[1,2-d]thiophene, 1-methylbenzo[b]-naphtho[2,1-d]thiophene, 6-methylbenzo[b]naphtho[2,1-d]thiophene and 4-methylbenzo[b]naphtho[2,3-d]thiophene demonstrated mutagenic activity. However, activity was observed only at high concentrations of the metabolic activator.

Sulphur heterocycles in coal-derived products: Relation between structure and abundance

Abstract Sulphur heterocycles in a coal tar and in a coal liquid vacuum residue were isolated by ligand exchange chromatography using PdCl2 on silica gel. Subsequent fractions were analysed by capillary column gas chromatography and gas chromatography-mass spectrometry. Two new selective stationary phases (a smectic liquid-crystalline polysiloxane and a biphenyl polysiloxane), as well as a methylpolysiloxane, were used to resolve the numerous isomers. All major sulphur heterocycles with 3–6 rings were identified by comparison of retention times of mixture components with those of standard reference compounds. The structures and relative abundances of the major sulphur heterocycles were analogous to those of the major polycyclic aromatic hydrocarbons in the same or similar samples.

Response-intensity modulation in long-range heteronuclear two-dimensional NMR chemical-shift correlation

Two-dimensional NMR spectroscopy has had a very significant impact on the way in which structure elucidation and spectral assignment studies are performed. Investigators have begun to exploit long-range heteronuclear coupling constants by utilizing delays in the conventional 2D NMR heteronuclear chemical-shift correlation experiment optimized for long-range magnetization transfer through two, three, and/or four bonds (‘Jcu, 3JcH, and “J,,) (1-16). Alternatively, several new experiments specifically for the observation of long-range heteronuclear spin-coupling information (14, 15, 2 7-22) have been reported. Despite the now numerous applications of longrange heteronuclear chemical-shift correlation contained in the literature, factors affecting the magnetization transfer step in these experiments have not been carefully investigated. Most long-range experiments are optimized for a 10 Hz magnetization transfer based upon the work of Reynolds and co-workers (2) or that of Wemly and Lauterwein (9), although other optimizations have also been used with success (I, 4, 10). As a consequence of the absence of responses in some of our own work despite optimization of the experiment at or near the magnitude of the coupling in question we now wish to communicate the results of our preliminary investigation into factors affecting response intensity in long-range heteronuclear chemical-shift correlation. Schenker and von Philipsborn (23) have reported a systematic investigation of the optimization of the INEPT and DEPT experiments in weakly coupled spin-f systems. They have shown that when magnetization is transferred via small heteronuclear couplings, that the transfer may be modulated by other homoand/or heteronuclear spin couplings which are experienced by those nuclei involved in the polarization transfer. Population transfer involved in the long-range heteronuclear chemical-shift correlation experiments may also be modulated in similar fashion, as recently suggested by Freeman (18) and Bax (21).

Determination and mutagenic activity of nitrogen-containing thiophenic compounds in coal-derived products

Abstract Polycyclic aromatic compounds containing both nitrogen and sulphur heteroatoms in aromatic rings were determined in a coal-derived liquid and a coal tar by capillary column gas chromatography and gas chromatography-mass spectrometry. G.c. with a flame photometric detector was used to analyse the nitrogen-containing polycyclic aromatic compound fraction obtained by adsorption chromatography on neutral alumina. The four possible isomers of the azadibenzothiophenes, and various other azathiophenic compounds, were positively identified by comparison with retention data of newly synthesized standard compounds. The aminodibenzothiophenes were the major nitrogen/sulphur-containing heterocycles in the coal liquid, while the azathiophenic compounds were the major ones in the coal tar. The differences between the two coal-derived products were related to the reaction conditions during their production. The four isomers of the azadibenzothiophenes were assayed for mutagenicity using the Ames test and compared with the mutagenicities previously reported for the aminodibenzothiophenes. It was found that the azadibenzothiophenes were not mutagenic, as opposed to the aminodibenzothiophenes.

A Reinvestigatton of the 13C-NMR Chemical Shift Assignments of Fluoranthene

Abstract Disparities in the protonated carbon NMR chemical shift assignments of the polynuclear aromatic molecule, fluoranthene, have been noted. Using two-dimensional 13C- 13C double quantum coherence, the 13C-NMR chemical shift assignments were reinvestigated and a set of unequivocal assignments obtained.