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We observed that Friedel-Crafts alkylation of unsaturated fatty acids yielded diverse products because of the shift and rearrangement of carbocation. However, these shifts and rearrangement rules of carbocation in Friedel-Crafts alkylation were unclear. For a better understanding of these rules, the product diversity of Friedel-Crafts alkylation of oleic acid with phenyl was studied by GC-MS. The product structures were identified by the characteristic m/z obtained in electron impact ionization and the relative contents of diverse isomers were calculated by the normalization method of integration areas in extracted ion and total ion chromatograms. The results suggested there were 11 isomeric compounds, 7~17-phenyl stearic acids with relative contents ranging from 2.9% to 16.4%. The inhibition factor of the shift and rearrangement of carbocation was also being investigated. The carbocation was easily quenched by oxygen-containing compounds such as ester, ether, and alcohol. Intramolecular quenching stopped the carbocation shifting and inhibited 2~6-phenyl stearic acids formation. The study contributed to the understanding of the shift and rearrangement of carbocation, diversity of produced isomers and inhibitors in Friedel-Crafts alkylation of the unsaturated fatty acids, which were helpful in preparing and manufacturing relative unsaturated fatty acids by alkylation.

Biosurfactants show synergic effects with synthesized surfactant in reducing hydrophobic/hydrophilic interfacial tension, while the understanding of the synergistic mechanism is limited. In the present work, mixed monolayers of surfactin and branched alkylbenzene sulfonate at the n-decane/water interface were studied using atomistic molecular dynamics simulations, and the presence of surfactin affecting the microstructure and dynamic properties of the mixed monolayer was evaluated at molecular level. The density distributions of the surfactants along the direction normal to the interface, radial distribution functions of the surfactant head groups, hydrophobic contacts between surfactants, translational activities of both surfactants and counterions, and the dynamics of the hydrogen bonds formed between surfactant and water were calculated. The results suggested that the structure of the mixed monolayers was more compact than that of the individual system of alkylbenzene sulfonate and the interfacial tension was more efficiently reduced, and the translational activities of both surfactants within the mixed monolayers were much lower. The results implied that biosurfactant surfactin and alkylbenzene sulfonate mixed well at the n-decane/water interface, though they were both anionic surfactants.

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