Incorporation of steroidal biomarkers into petroleum model compounds

Abstract

A series of fully‐substituted 5,6‐benzoquinolines covalently fused to the chlolestane framework has been synthesized to serve as model compounds for the poorly characterized components found in the heaviest fractions of petroleum, namely the asphaltenes. Acid‐catalyzed cyclocondensation of an aromatic imine with 5‐α‐cholestan‐3‐one gives 5,6‐benzoquinoline cycloadducts incorporating the steroidal biomarker fused to the benzoquinoline system at the 3,4‐positions, with various pendent substituents in the 2‐position. X‐ray crystallography of three such derivatives shows that the solid‐state geometries of these molecules are quite similar, and packing in the solid state appears to be dominated to a great extent by the nature of the pendent substituent. X‐ray crystallography and solution phase circular dichroism spectroscopy together suggest that the conjugated benzoquinoline moiety adopts a helical conformation. Copyright © 2012 John Wiley & Sons, Ltd.

Aggregation of asphaltene model compounds using a porphyrin tethered to a carboxylic acid

“…58, 59 Interestingly, the maximum is observed in the Job's plot at a mole fraction of 0.3 for 3, suggesting a 1:2 complex between the porphyrin acid 3 and model compound 4, respectively. Nonlinear curve fitting, considering both binding25 events, namely self-association of 3 (K dim = 390 ± 27 M -1 ) and a 1:2 binding model, results in an overall association constant of 1.23 ± 0.1 × 10 6 M -2 .60 The formation of a 1:2 complex between model compounds 3 and 4 would be in line with the results of Tan et al, who report…”

“…As only 20 weak binding was observed, a second titration with a 1.25 mM solution of phenylacetic acid was performed allowing addition up to 8 equivalents of 4. Both titrations gave concentration dependent changes for the chemical shift for the signal of the methylene protons of phenylacetic acid, but the binding was quite 25 lower compared to pyridine, with an averaged K assoc = 24 ± 8 M -1 (see SI), obtained from the two titrations detailed above. In general, it is know that substitution in the 2,6-positions of the pyridyl-ring has an impact on basicity, e.g., for pyridine, 2,6lutidine, and 2,6-diisopropylpyridine, pK a = 4.38, 5.77, and 5.34, 30 respectively.…”

“…3 Asphaltenes are commonly known to cause problems for a variety of practical processes, such as transportation, storage, and refining. [2][3][4] To solve these issues, significant efforts have been 25 expended to understand the bulk behavior of asphaltenes, 2, 4, 5 and these efforts have even suggested that the carbon-rich and heteroatom doped composition of asphaltenes might yield materials for electronic devices. 6,7 In spite of these studies, however, the general molecular structure of the asphaltenes 30 remains to be resolved, 8 and a major barrier to the goal is the formation of very stable aggregates between individual molecules that complicates many analysis techniques.…”

Synthesis and Aggregation Behavior of Chiral Naphthoquinoline Petroporphyrin Asphaltene Model Compounds

“…The synthesis of archipelago model porphyrin compounds was next pursued, starting from readily available aldehydes 10 a – c (Scheme ) . Aldehydes 10 a – b were synthesized by following reported protocols, using phosphonium salts 7 a and 7 b , which were easily prepared from commercially available chloromethylarenes and PPh 3 . Pyrene derivative 10 c was prepared in an orthogonal manner, to avoid the use of prohibitively expensive 1‐(chloromethyl)pyrene (Scheme ) .…”

“…Unfortunately, the limited range of commercial porphyrin compounds in turn limits, and even biases, analytical results and conclusions. As a result, we have worked to develop efficient protocols for the synthesis of larger and more diverse structural representatives of the asphaltenes ,. Inspired by discoveries of Prowse and Maxwell (Figure c) and motivated by our fundamental interest in porphyrin derivatives as a potential driver of asphaltene aggregation, we elected to combine known asphaltene structural features into individual model compounds, fusing a functionalized polycyclic aromatic fragment to a steroidal biomarker and a metalloporphyrin into a series of “chimeric” model asphaltene compounds.…”