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The volatile aromatic fraction (240 °C and 10–3 Torr pressure) of Athabasca bitumen was separated via thin-layer chromatography (TLC) (Ag+/SiO2), followed by alumina column chromatography, into 13 ...

The molecular-weight (MW)-dependent fluorescence of asphaltene discovered over 20 years ago has been re-examined from a theoretical point of view. It is concluded here that the dependence is a result of the sensitivity of the jump between the non-intersecting potential energy surfaces involved in the S1 → S0 internal conversion to the excitation energy of the S1 state, the energy gap, ΔE. The excitation energy of organoaromatic molecules, in general, depends upon the size of the aromatic chromophore which, in turn, has been shown to increase with the MW of the gel-permeation-chromatographic (GPC)-separated fractions of asphaltene. The larger the chromophore size, the lower the excitation energy of the S1 state. This then leads to an increase of the vibrational Franck−Condon factor governing the rate of internal conversion k(IC)∼1013fv∼1013exp(−αΔE) where fv is the Franck−Condon factor and α is a proportionality constant. As ΔE decreases, the rate of the S1 → S0 transition increases in competition with the...

Relying on experimental and theoretical data available from the literature, it is shown that the conclusions derived from measurements of fluorescence decay and depolarization kinetic times as reported in a series of papers over the past decade (Ralston, et al. Energy Fuels 1996, 10, 623–630; Groenzin, et al. J. Phys. Chem. A 1999, 103, 11237–11245; Groenzin, et al. Energy Fuels 2000, 14, 677–684; Buenzostro-Gonzales, et al. Energy Fuels 2001, 15, 972–979; Groenzin, H., et al. Energy Fuels 2003, 17, 498–503; Badre, S., et al. Fuel 2005, 85, 1–11 and references therein) are egregiously wrong. To start with, the decay time measurements were done with inappropriate instrumentation which resulted in misleading results. Misinterpretation of the results led to the mistaken conclusion that bichromophoric type molecules are absent from petroleum asphaltene and therefore the architecture of the asphaltene molecule features a single condensed cyclic core spiked with some alkyl chains, in spite of irrefutable chemic...

It is shown by sequential reprecipitation that both n-C5 and n-C7 Athabasca asphaltene contain significant amounts of precipitant solubles, comprising resins and low-molecular-weight asphaltene-like substances in about the same percentage amounts relative to the residual precipitated insoluble asphaltene. All of the several hundred resinous molecules detected in the n-C5 solubles, with some minor exceptions, were also detected in the resin fraction of the maltene. From an estimation of the concentrations of several compound classes in the solution and solid asphaltene phases, values were derived for the equipartitioning coefficients. The results implicate aromatic stacking as the dominant mode of association of resins and asphaltene. The aggregate amount of n-C5 solubles associated with the n-C5 insoluble plus the aggregate amount of n-C7 solubles associated with the n-C7 insoluble residual asphaltene obtained in the sixth reprecipitation is more than 50% of the latter, and in the native oil, it is estima...

Covalent structural features and the biomarker content of an immature asphaltene originating from a saline lake deposit in China have been explored in ruthenium-ions-catalyzed oxidation. This process converts aromatic-attached aliphatic appendages to their carboxylic acid derivatives, the carboxylic group representing the site of attachment to the aromatic ring. The kinds of products were similar to those found from mature crude oil asphaltenes with slightly but significantly different distributions. The main structural features identified were, in decreasing order of importance, alkenyl bridges between aromatic carbons (including aromatic condensed cyclohexanes) followed by aromatic-attached n-alkyl, isoprenoid, and α-C 1 -C 3 branched n-alkyl side chains. The major cyclic biomarkers detected were all attached to aromatic carbons by a single C-C bond and comprised gammacerane, C 27 -C 35 hopanes, C 27 -C 29 regular steranes, 4-methyl steranes, C 20 -C 23 pregnanes, C 20 -C 24 cheilanthanes, etc., each with a specific position in the molecule as the attachment site. Additional products-as found with other asphaltenes-were benzene dithrough hexacarboxylic acids, useful indicators of the mode of aromatic condensation in the asphaltene.

After some general comments on the concept of asphaltene, outstanding problems relating to the molecular structure of Athabasca asphaltene are discussed in light of new results on aromatic-attached appendages derived from ruthenium-ions-catalyzed oxidation (RICO). Detected were homologous series of α-branched C1−C4 n-alkyl side chains up to C30−C40 in an aggregate amount of ∼10% of the n-alkyl side chains, C15−C20 regular isoprenoids, C20−C28 cheilanthanes, C27−C32 hopanes, C27−C29 steranes, C21−C24 pregnanes, and a number of branched hydrocarbons giving hydroxy carboxylic acids. The nature and distribution of these aromatic-attached biomarkers are similar but not identical to those reported to be attached to the asphaltene via a sulfide bridge. They may have originated from secondary biotic sources and became incorporated into the asphaltene via a Friedel−Crafts-type reaction. Additional, previously not considered reactions in the RICO of asphaltene are described, and aspects of the analytical procedures...

The molecular structural units of Boscan and Duri asphaltenes have been investigated in ruthenium-ion-catalyzed oxidation (RICO) and pyrolysis. From the RICO reactions, homologous series of n-alkanoic acids (C1−C31), representing aromatic-attached n-alkyl side chains, α,ω-di-n-alkanoic acids (C4−C26), representing polymethylene bridges connecting two aromatic units, and benzenecarboxylic acids, indicating the major modes of aromatic condensations in the asphaltene molecules and the minor role of pericondensed aromatic structures in them, were detected and measured. The RICO reaction also yielded a nondistillable oxidized residue. Pyrolysis of this material after methylation yielded a homologous series of n-alkanes and n-alk-1-enes, n-alkanoic and n-alkenoic acid methyl esters, and free n-alkanoic acids with strong even-to-odd carbon preference. These products prove the presence of naphthenic-attached n-alkyl side chains and bridges, polymethylene bridges connecting aromatic to naphthenic systems, and n-al...

It is only since 1985 that the absolute rate constanss have been measured for some reactions of divalent silylene species. In this article the absolute rate constant data reported to date for the reactions of SiH2, SiMe2, SiMePh, SiHCl, SiCl2, SiF2 and SiBr2 are reviewed and, where possible, mechanistic pathways discussed. The reactivity of silylenes is, in general, much higher than had previously been estimated on the basis of relative rate studies.

From detailed chemical and thermal degradation studies, a host of structural units have been identified in Alberta asphaltenes. It has been shown that the extent of aromatic condensation is low and that highly condensed pericyclic aromatic structures are present in very low concentrations. From the available data reported to date, it is concluded that petroleum asphaltenes were mainly derived through the catalytic cyclization, aromatization and condensation of n -alkanoic, probably fatty acids, precursors.

Ru ion catalyzed oxidation (RICO) has been used to probe the structural details of asphaltene molecules from Athabasca bitumen. The ability of RICO to remove nearly quantitatively aromatic carbons while leaving aliphatic and naphthenic structures essentially unaffected has been exploited for the quantitative determination of the following structural features : (1) the distribution of n-alkyl chains attached to aromatic carbons with respect to chain length, total number of n-alkyl chains and the number of carbon atoms in them; (2) the distribution of polymethylene bridges connecting two aromatic units with respect to bridge length, total number of bridges, and the number of carbon atoms in them; (3) the fractional amount of total sulfur present as saturated sulfides

A flash pyrolysis method has been employed, allowing the production of pyrolysis oil from Athabasca asphaltene on the multigram scale, for the identification of homologous series of n-alkylbenzenes, 9-n-alkylfluorenes, and 1-n-alkyldibenzothiophenes. These aromatic classes of compounds were concentrated from the pyrolysis oil by a sequence of selective oxidative and chromatographic steps. Identification was based on comparison of GC retention times and mass spectra with those of synthetic standards or with literature values

Using a combination of instrumental and chemical methods, many new classes of compounds appearing as homologous series have been detected in Athabasca oil sand bitumen and in the chemical and thermal degradative products of asphaltene and the heavy ends of maltene. In general, the volatile portion of the maltene is rich in cyclic terpenoid structures and devoid in aliphatic compounds or normal alkane-derived cyclic molecules while the asphaltene fraction and heavy ends of maltene are abundant in normal alkyl-substituted aromatics, thianes, thiolanes, thiophenes, benzo- and dibenzothiophenes. This paper reports that Ru(VIII)-catalyzed oxidation permitted the quantitative estimation of the n-alkyl groups attached to aromatic carbons and of n-alkyl bridges between two aromatic units and their concentration distribution according to chain length. It also showed the presence of a large naphthenic core containing cyclic sulfides, which, during oxidation, were converted to their sulfones.

The gas-phase addition of S( 3 P J ) atoms to cis- and trans-butene-2 has been investigated and both reactions have been shown to be 100% stereospecific, yielding the lowest excited triplet state of the 2,3-dimethylthiirane end product. The triplet thiirane has a long collisional lifetime and is capable of undergoing facile, reversible addition to the butenes causing their geometrical isomerization, while retaining its own original geometry. The cause of the gradual loss of stereospecificity in the 2,3-dimethylthiirane product with increasing conversion has been identified at this geometrical isomerization of the butene-2 substrate by the primary triplet thiirane and those produced in the secondary photolysis of the thiirane product. The NMR spectra of the isomerically pure cis- and trans-2,3 dimethylthiiranes have been obtained and assigned by computer simulation

It is only since 1985 that the absolute rate constanss have been measured for some reactions of divalent silylene species. In this article the absolute rate constant data reported to date for the reactions of SiH2, SiMe2, SiMePh, SiHCl, SiCl2, SiF2 and SiBr2 are reviewed and, where possible, mechanistic pathways discussed. The reactivity of silylenes is, in general, much higher than had previously been estimated on the basis of relative rate studies.

The 4n-r electron heterocycles oxirene, thiirene and 2-azirine are expected to be antiaromatic and therefore inherently unstable. In the past decade isotopic labelling and chemical scavenging experiments have provided compelling, although indirect evidence for the transient existence of these molecules in a variety of reactions but to date only thiirene has been isolated and characterized, using low temperature matrix isolation techniques. Vibrational assignments for thiirene and its deuterated analogs were made possible by means of a normal coordinate analysis based on computed abinitio optimized geometries. Monoand dimethyl-, trifluoromethyl, bis(trifluoromethyl), benzoand methylcarboethoxythiirene have also been synthesized. Recent abinitio molecular orbital calculations on the thermodynamic stabilities of the C2H2O and C2H2S isomers provide a useful framework for the elucidation of the various interconversions observed in the photolysis of the source compounds a-diazoketones and 1,2,3-thiadiazoles. The extent of oxirene participation in the Wolff rearrangement (WR) is primarily governed by the relative rates of the ketocarbene-oxirene and ketocarbene-ketene interconversions which, in turn, depend on the nature of the substituents. Other important factors include the phase, nature of the solvent, and the wavelength of irradiation. In addition to isomerization, oxirene and thiirene can depose to acetylene + O (or 5). The available data on 2-azirine are not very extensive but evidence for its transient existence as an intermediate, e.. in the decomposition of benzotriazoles, is very compelling. Abinitio MO calculations have been carried out on the singlet and triplet energy manifolds of some of the C2H3N isomers.