Synthesis and Aggregation Behavior of Chiral Naphthoquinoline Petroporphyrin Asphaltene Model Compounds

Abstract

The synthesis of structurally relevant compounds that model the chemical behavior and supramolecular aggregation of the asphaltenes, the most polar and metal-rich fraction of heavy petroleum, has been extended to include fusions of important petroleum biomarkers. The synthetic protocol features a multicomponent reaction to form a dyad composed of a fused steroidal naphthoquinoline, followed by a pyrrole cyclocondensation reaction to incorporate the dyad into a chiral triad containing a Ni -porphyrin substituent. This synthetic protocol has been used to prepare large molecules that represent both "continental" and "archipelago" models of asphaltene composition. The steroid-naphthoquinoline-porphyrin triads have been studied by UV/Vis and circular dichroism (CD) spectroscopies, and the results suggest that the naphthoquinoline core, a tetrahydro[4]helicene, adopts a helical conformation, producing a CD signal electronically related to the characteristic Soret absorption band of the porphyrin subunit. Finally, supramolecular aspects of asphaltene aggregation have been examined on a molecular level through analysis of axial coordination of pyridine to the Ni-porphyrin. The relative affinity of pyridine for binding to the Ni center of the porphyrin is evaluated by comparing binding propensities in a series of sterically differentiated substituted porphyrins.

Shared Depletion and Restabilization Colloidal Interactions in Phase Diagrams for Silica Nanoparticle and Asphaltene + Polystyrene + Solvent Mixtures

“…These “primary aggregates” have an even greater number of potential possibilities for cluster and floc formation, reflected in the range of reported scattering coefficients and mean sizes reported for them. ,,− The two properties that “primary aggregates” share with silica nanoparticles is that cluster and floc formation in organic solvents have a dispersion energy ∼ kT and that cluster formation is reversible. In contrast, breaking “primary aggregates” down into smaller structures or into individual molecules or extracting molecules from “primary aggregates” requires overcoming significant energy barriers. − Chemically separated Athabasca pentane asphaltenes and physically separated asphaltene-rich retentate would appear to share this behavioral property.…”

Steroid diversification by multicomponent reactions

“…In this context, Schulze et al . optimized a multicomponent cyclocondensation reaction [50–51] between 5α-cholestan-3-one ( 43 ), aromatic aldehydes and 2-aminoanthracene ( 51 ) for the generation of steroidal naphthoquinolines as synthetic asphaltene models for the study of their physical properties. As shown in Scheme 16, the synthetic approach was based on Kozlov–Wang MCR [52], in which an aromatic aldehyde, 2-aminoanthracene and tetrahydropyran-4-one react in the presence of I 2 as catalyst.…”

Effects of Styrene Ionomers on the Dispersion of Asphaltenes in Crude Heavy Oil

“…400 to ca. 2300, depending on the sources of heavy oil and the types of molecular weight measurement methods, − and can be dissolved in benzene or toluene. ,− Asphaltenes (∼1.5 nm) have pericondensed aromatic ring structures with peripheral alkane chains and polar functional groups attached to them; the so-called “continental model”, “island model”, and “archipelago model” are developed to describe the complicated architecture of asphaltene molecules. ,,− These asphaltenes tend to self-assemble and precipitate in oil. − According to the Yen-Mullins model of asphaltene aggregation, ,,, the polar functional groups and aromaticity of the asphaltene molecules allow interactions with other asphaltene molecules, forming “asphaltene nanoaggregates” (∼2 nm) with 6–10 asphaltene molecules. − These nanoaggregates can further form “asphaltene clusters” with 6–10 asphaltene nanoaggregates (∼5 nm) ,− ,− possibly through diffusion-limited cluster aggregation and/or reaction-limited cluster aggregation mechanisms . It is suggested that asphaltene nanoaggregates are less aromatic and have open fractal structures. , On the other hand, the formation of asphaltene clusters is entropically driven, as there are fewer functional groups compared to bulk asphaltene molecules, and the interactions between nanoaggregates are much less specific than those between single molecules …”