A systematic theoretical study is carried out on the mechanism for Pd(II)-catalyzed oxidative cross-coupling between electron-deficient arenes and alkenes. Two types of reaction pathways involving either a sequence of initial arene C-H activation followed by alkene activation, or the reverse sequence of initial alkene C-H activation followed by arene activation are evaluated. Several types of C-H activation mechanisms are discussed including oxidative addition, σ-bond metathesis, concerted metalation/deprotonation, and Heck-type alkene insertion. It is proposed that the most favored reaction pathway should involve an initial concerted metalation/deprotonation step for arene C-H activation by (L)Pd(OAc)(2) (L denotes pyridine type ancillary ligand) to generate a (L)(HOAc)Pd(II)-aryl intermediate, followed by substitution of the ancillary pyridine ligand by alkene substrate and direct insertion of alkene double bond into Pd(II)-aryl bond. The rate- and regio-determining step of the catalytic cycle is concerted metalation/deprotonation of arene C-H bond featuring a six-membered ring transition state. Other mechanism alternatives possess much higher activation barriers, and thus are kinetically less competitive. Possible competing homocoupling pathways have also been shown to be kinetically unfavorable. On the basis of the proposed reaction pathway, the regioselectivity predicted for a number of monosubstituted benzenes is in excellent agreement with experimental observations, thus, lending further support for our proposed mechanism. Additionally, the origins of the regioselectivity of C-H bond activation is elucidated to be caused by a major steric repulsion effect of the ancillary pyridine type ligand with ligands on palladium center and a minor electronic effect of the preinstalled substituent on the benzene ring on the cleaving C-H bond. This would finally lead to the formation of a mixture of meta and para C-H activation products with meta products dominating while no ortho products were detected. Finally, the multiple roles of the ancillary pyridine type ligand have been discussed. These insights are valuable for our understanding and further development of more efficient and selective transition metal-catalyzed oxidative C-H/C-H coupling reactions.

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In this study, profiles of chemical characterization, oxidative stability, and in vitro antioxidant capacity of sesame oils obtained from supercritical and subcritical techniques and conventional methods are studied and compared. The results shows that a large proportion of fatty acid and triacylglycerol are not significantly influenced by the processing technologies (except for LLLn, SOA, C18:3n‐6, and C22:0). However, significant differences of minor component, oxidation stability, and free radical scavenging activity among the test oil samples are observed. Supercritical sesame oils are more excellent than the subcritical sesame oils and oils obtained from the traditional methods, especially in terms of γ‐tocopherol, lignan and polyphenol contents, and antioxidant capacity, thus indicating that CO2 fluid technology is a desirable alternative to extract sesame oils with rich nutrition and superb physiological activity. Further, oils obtained from roasted sesame seeds exhibited higher oxidative stability and antioxidant capacity, thus declaring that high temperature roasting was a critical issue that influenced the quality of the final sesame oil product. Practical Applications: This study used two burgeoning technologies, namely supercritical and subcritical techniques for the practical applications of the extraction process of sesame oils from sesame (Sesamum indicum, L.) seeds. Supercritical fluid was an excellent technology to selectively extract bioactive compounds from sesame by using CO2 as a carrier solvent. The use of CO2 supercritical fluid in the present study was associated with high efficiency and antioxidant activities of the obtained sesame oils. These results indicate that this technology was an efficient and rapid method for extracting phytochemicals when compared with the conventional methods (hot pressing, cold pressing, solvent extraction, and aqueous extraction), thus indicating that it had the potential to work as a satisfactory approach to produce specific sesame oil products for health care and cosmetic use. This method can be easily implemented on an industrial scale. In this study, profiles of chemical characterization, oxidative stability, and in vitro antioxidant capacity of sesame oils obtained from supercritical and subcritical techniques and conventional methods are studied and compared. PCA and HCA show apparent distinctions between the supercritical sesame oils and the other kinds, as well as between the roasted and unroasted sesame oils. Models deduced by MLR are all significant, which are recognized as satisfactory and acceptable for predicting the in vitro antioxidant abilities of the sesame oils.

In this study, the concentrations of three lignans in 100 sesame seeds and 56 sesame oils were determined using a newly developed method based on high‐performance liquid chromatography coupled with a UV/Vis detector. Total lignan contents in sesame seed and oil samples ranged from 2.52 to 12.76 and 3.38 to 11.53 mg/g, respectively. Black sesame seeds showed higher sesamin content (range 1.98–9.41 mg/g, mean 4.34 mg/g) and sesamolin content (range 1.06–3.35 mg/g, mean 1.92 mg/g) than the other three varieties of sesame seeds. Black sesame oils had higher contents of lignans than the white sesame oils, although remarkable differences were not observed. Hot pressed and small mill sesame oils expressed higher contents of sesamol, sesamin, and total lignans than the cold pressed and refined sesame oils. The results revealed that there is extensive variability in lignan concentration in sesame oils and seeds.

Treatment with three adsorbents led to reductions of PAHs in sesame oils, and activated carbons are more effective for removal of PAHs than activated clay under the experimental conditions. Fatty acid, triacylglycerol, and γ‐tocopherol profiles of sesame oils are not significantly influenced by addition of any adsorbents. However, significant differences (P < 0.05) are observed in the contents of other minor components, oxidation stability and free radical scavenging capacity between the crude and treated sesame oils. Polyphenol and phytosterol are good predictors of oxidative stability and antioxidant capacity of sesame oils, due to significant correlations are observed. Although adsorption process may bring disadvantage to sesame oils such as reductions of beneficial constituents related to storage stability, free radical scavenging capacity and other physiological functions, however, to eliminate the contamination of PAHs, treatment with activated carbon during sesame oil purification is highly recommended in order to reduce the risk of consumption and to assure the consumer health. Moreover, these results provide a useful guidance for sesame oil plant to improve the quality of the final oil product. Practical Applications: Results of this study can be applied to sesame oil plants and are transferable to other flavor edible oils for which lower the risk of consumption and bring economic and social advantages to manufacturers to guarantee the oil quality and consumer health. In this work, the contents of polycyclic aromatic hydrocarbon, lipid characteristic, oxidative stability, and free radical scavenging capacity of sesame oil during adsorption process are investigated and compared. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed apparent distinctions between the crude and treated sesame oils, thus illustrated that adsorption is a double‐edged sword to sesame oils.